FOCAS Tier-C PR C — IPC path end-to-end: Proxy IpcFocasClient + Host FwlibFrameHandler + IFocasBackend abstraction. Third of 5 PRs for #220. Ships the wire path from IFocasClient calls in the .NET 10 driver, over a named-pipe (or in-memory stream) to the .NET 4.8 Host's FwlibFrameHandler, dispatched to an IFocasBackend. Keeps the existing IFocasClient DI seam intact so existing unit tests are unaffected (172/172 still pass). Proxy side adds Ipc/FocasIpcClient (owns one pipe stream + call gate so concurrent callers don't interleave frames, supports both real NamedPipeClientStream and arbitrary Stream for in-memory test loopback) and Ipc/IpcFocasClient (implements IFocasClient by forwarding every call as an IPC frame — Connect sends OpenSessionRequest and caches the SessionId; Read sends ReadRequest and decodes the typed value via FocasDataTypeCode; Write sends WriteRequest for non-bit data or PmcBitWriteRequest when it's a PMC bit so the RMW critical section stays on the Host; Probe sends ProbeRequest; Dispose best-effort sends CloseSessionRequest); plus FocasIpcException surfacing Host-side ErrorResponse frames as typed exceptions. Host side adds Backend/IFocasBackend (the Host's view of one FOCAS session — Open/Close/Read/Write/PmcBitWrite/Probe) with two implementations: FakeFocasBackend (in-memory, per-address value store, honors bit-write RMW semantics against the containing byte — used by tests and as an OTOPCUA_FOCAS_BACKEND=fake operational stub) and UnconfiguredFocasBackend (structured failure pointing at docs/v2/focas-deployment.md — the safe default when OTOPCUA_FOCAS_BACKEND is unset or hardware isn't configured). Ipc/FwlibFrameHandler replaces StubFrameHandler: deserializes each request DTO, delegates to the IFocasBackend, re-serializes into the matching response kind. Catches backend exceptions and surfaces them as ErrorResponse{backend-exception} rather than tearing down the pipe. Program.cs now picks the backend from OTOPCUA_FOCAS_BACKEND env var (fake/unconfigured/fwlib32; fwlib32 still maps to Unconfigured because the real Fwlib32 P/Invoke integration is a hardware-dependent follow-up — #220 captures it). Tests: 7 new IPC round-trip tests on the Proxy side (IpcFocasClient vs. an IpcLoopback fake server: connect happy path, connect rejection, read decode, write round-trip, PMC bit write routes to first-class RMW frame, probe, ErrorResponse surfaces as typed exception) + 6 new Host-side tests on FwlibFrameHandler (OpenSession allocates id, read-without-session fails, full open/write/read round-trip preserves value, PmcBitWrite sets the specified bit, Probe reports healthy with open session, UnconfiguredBackend returns pointed-at-docs error with ErrorCode=NoFwlibBackend). Existing 165 FOCAS unit tests + 24 Shared tests + 3 Host handshake tests all unchanged. Total post-PR: 172+24+9 = 205 FOCAS-family tests green. What's NOT in this PR: the actual Fwlib32.dll P/Invoke integration inside the Host (FwlibHostedBackend) lands as a hardware-dependent follow-up since no CNC is available for validation; supervisor + respawn + crash-loop breaker comes in PR D; MMF + NSSM install scripts in PR E.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ZB.MOM.WW.OtOpcUa.slnx

@@ -14,6 +14,8 @@
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj"/>
+        <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.csproj"/>
+        <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Client.Shared/ZB.MOM.WW.OtOpcUa.Client.Shared.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Client.CLI/ZB.MOM.WW.OtOpcUa.Client.CLI.csproj"/>
@@ -34,12 +36,18 @@
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Client.Shared.Tests/ZB.MOM.WW.OtOpcUa.Client.Shared.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Client.CLI.Tests/ZB.MOM.WW.OtOpcUa.Client.CLI.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Client.UI.Tests/ZB.MOM.WW.OtOpcUa.Client.UI.Tests.csproj"/>

docs/drivers/AbLegacy-Test-Fixture.md

@@ -0,0 +1,125 @@
+# AB Legacy test fixture
+
+Coverage map + gap inventory for the AB Legacy (PCCC) driver — SLC 500 /
+MicroLogix / PLC-5 / LogixPccc-mode.
+
+**TL;DR:** Docker integration-test scaffolding lives at
+`tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/` (task #224),
+reusing the AB CIP `ab_server` image in PCCC mode with per-family
+compose profiles (`slc500` / `micrologix` / `plc5`). Scaffold passes
+the skip-when-absent contract cleanly. **Wire-level round-trip against
+`ab_server` PCCC mode currently fails** with `BadCommunicationError`
+on read/write (verified 2026-04-20) — ab_server's PCCC server-side
+coverage is narrower than libplctag's PCCC client expects. The smoke
+tests target the correct shape for real hardware + should pass when
+`AB_LEGACY_ENDPOINT` points at a real SLC 5/05 / MicroLogix. Unit tests
+via `FakeAbLegacyTag` still carry the contract coverage.
+
+## What the fixture is
+
+**Integration layer** (task #224, scaffolded with a known ab_server
+gap):
+`tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/` with
+`AbLegacyServerFixture` (TCP-probes `localhost:44818`) + three smoke
+tests (parametric read across families, SLC500 write-then-read). Reuses
+the AB CIP `otopcua-ab-server:libplctag-release` image via a relative
+`build:` context in `Docker/docker-compose.yml` — one image, different
+`--plc` flags. See `Docker/README.md` §Known limitations for the
+ab_server PCCC round-trip gap + resolution paths.
+
+**Unit layer**: `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/` is
+still the primary coverage. All tests tagged `[Trait("Category", "Unit")]`.
+The driver accepts `IAbLegacyTagFactory` via ctor DI; every test
+supplies a `FakeAbLegacyTag`.
+
+## What it actually covers (unit only)
+
+- `AbLegacyAddressTests` — PCCC address parsing for SLC / MicroLogix / PLC-5
+  / LogixPccc-mode (`N7:0`, `F8:12`, `B3:0/5`, etc.)
+- `AbLegacyCapabilityTests` — data type mapping, read-only enforcement
+- `AbLegacyReadWriteTests` — read + write happy + error paths against the fake
+- `AbLegacyBitRmwTests` — bit-within-DINT read-modify-write serialization via
+  per-parent `SemaphoreSlim` (mirrors the AB CIP + FOCAS PMC-bit pattern from #181)
+- `AbLegacyHostAndStatusTests` — probe + host-status transitions driven by
+  fake-returned statuses
+- `AbLegacyDriverTests` — `IDriver` lifecycle
+
+Capability surfaces whose contract is verified: `IDriver`, `IReadable`,
+`IWritable`, `ITagDiscovery`, `ISubscribable`, `IHostConnectivityProbe`,
+`IPerCallHostResolver`.
+
+## What it does NOT cover
+
+### 1. Wire-level PCCC
+
+No PCCC frame is sent by the test suite. libplctag's PCCC subset (DF1,
+ControlNet-over-EtherNet, PLC-5 native EtherNet) is untested here;
+driver-side correctness depends on libplctag being correct.
+
+### 2. Family-specific behavior
+
+- SLC 500 timeout + retry thresholds (SLC's comm module has known slow-response
+  edges) — unit fakes don't simulate timing.
+- MicroLogix 1100 / 1400 max-connection-count limits — not stressed.
+- PLC-5 native EtherNet connection setup (PCCC-encapsulated-in-CIP vs raw
+  CSPv4) — routing covered at parse level only.
+
+### 3. Multi-device routing
+
+`IPerCallHostResolver` contract is verified; real PCCC wire routing across
+multiple gateways is not.
+
+### 4. Alarms / history
+
+PCCC has no alarm object + no history object. Driver doesn't implement
+`IAlarmSource` or `IHistoryProvider` — no test coverage is the correct shape.
+
+### 5. File-type coverage
+
+PCCC has many file types (N, F, B, T, C, R, S, ST, A) — the parser tests
+cover the common ones but uncommon ones (`R` counters, `S` status files,
+`A` ASCII strings) have thin coverage.
+
+## When to trust AB Legacy tests, when to reach for a rig
+
+| Question | Unit tests | Real PLC |
+| --- | --- | --- |
+| "Does `N7:0/5` parse correctly?" | yes | - |
+| "Does bit-in-word RMW serialize concurrent writers?" | yes | yes |
+| "Does the driver lifecycle hang / crash?" | yes | yes |
+| "Does a real read against an SLC 500 return correct bytes?" | no | yes (required) |
+| "Does MicroLogix 1100 respect its connection-count cap?" | no | yes (required) |
+| "Do PLC-5 ST-files round-trip correctly?" | no | yes (required) |
+
+## Follow-up candidates
+
+1. **Fix ab_server PCCC coverage upstream** — the scaffold lands the
+   Docker infrastructure; the wire-level round-trip gap is in ab_server
+   itself. Filing a patch to `libplctag/libplctag` to expand PCCC
+   server-side opcode coverage would make the scaffolded smoke tests
+   pass without a golden-box tier.
+2. **Rockwell RSEmulate 500 golden-box tier** — Rockwell's real emulator
+   for SLC/MicroLogix/PLC-5. Would close UDT-equivalent (integer-file
+   indirection), timer/counter decomposition, and real ladder execution
+   gaps. Costs: RSLinx OEM license, Windows-only, Hyper-V conflict
+   matching TwinCAT XAR + Logix Emulate, no clean PR-diffable project
+   format (SLC/ML save as binary `.RSS`). Scaffold like the Logix
+   Emulate tier when operationally worth it.
+3. **Lab rig** — used SLC 5/05 or MicroLogix 1100 on a dedicated
+   network; parts are end-of-life but still available. PLC-5 +
+   LogixPccc-mode behaviour + DF1 serial need specific controllers.
+
+## Key fixture / config files
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyServerFixture.cs`
+  — TCP probe + skip attributes + env-var parsing
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyReadSmokeTests.cs`
+  — three wire-level smoke tests (currently blocked by ab_server PCCC gap)
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/docker-compose.yml`
+  — compose profiles reusing AB CIP Dockerfile
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/README.md`
+  — known-limitations write-up + resolution paths
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs` —
+  in-process fake + factory
+- `src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs` — scope remarks
+  at the top of the file

docs/drivers/AbServer-Test-Fixture.md

@@ -0,0 +1,216 @@
+# ab_server test fixture
+
+Coverage map + gap inventory for the AB CIP integration fixture backed by
+libplctag's `ab_server` simulator.
+
+**TL;DR:** `ab_server` is a connectivity + atomic-read smoke harness for the AB
+CIP driver. It does **not** benchmark UDTs, alarms, or any family-specific
+quirk. UDT / alarm / quirk behavior is verified only by unit tests with
+`FakeAbCipTagRuntime`.
+
+## What the fixture is
+
+- **Binary**: `ab_server` — a C program in libplctag's
+  `src/tools/ab_server/` ([libplctag/libplctag](https://github.com/libplctag/libplctag),
+  MIT).
+- **Launcher**: Docker (only supported path). `Docker/Dockerfile`
+  multi-stage-builds `ab_server` from source against a pinned libplctag
+  tag + copies the binary into a slim runtime image.
+  `Docker/docker-compose.yml` has per-family services (`controllogix`
+  / `compactlogix` / `micro800` / `guardlogix`); all bind `:44818`.
+- **Lifecycle**: `AbServerFixture` TCP-probes `127.0.0.1:44818` at
+  collection init + records a skip reason when unreachable. Tests skip
+  via `[AbServerFact]` / `[AbServerTheory]` which check the same probe.
+- **Profiles**: `KnownProfiles.{ControlLogix, CompactLogix, Micro800, GuardLogix}`
+  in `AbServerProfile.cs` — thin Family + ComposeProfile + Notes records;
+  the compose file is the canonical source of truth for which tags get
+  seeded + which `--plc` mode the simulator boots in.
+- **Tests**: one smoke, `AbCipReadSmokeTests.Driver_reads_seeded_DInt_from_ab_server`,
+  parametrized over all four profiles via `[AbServerTheory]` + `[MemberData]`.
+- **Endpoint override**: `AB_SERVER_ENDPOINT=host:port` points the
+  fixture at a real PLC instead of the local container.
+
+## What it actually covers
+
+- Read path: driver → libplctag → CIP-over-EtherNet/IP → simulator → back.
+- Atomic Logix types per seed: `DINT`, `REAL`, `BOOL`, `SINT`, `STRING`.
+- One `DINT[16]` array tag (ControlLogix profile only).
+- `--plc controllogix` and `--plc compactlogix` mode dispatch.
+- The skip-on-missing-binary behavior (`AbServerFactAttribute`) so a fresh
+  clone without the simulator stays green.
+
+## What it does NOT cover
+
+Each gap below is either stated explicitly in the profile's `Notes` field or
+inferable from the seed-tag set + smoke-test surface.
+
+### 1. UDTs / CIP Template Object (class 0x6C)
+
+ControlLogix profile `Notes`: *"ab_server lacks full UDT emulation."*
+
+Unverified against `ab_server`:
+
+- PR 6 structured read/write (`AbCipStructureMember` fan-out)
+- #179 Template Object shape reader (`CipTemplateObjectDecoder` + `FetchUdtShapeAsync`)
+- #194 whole-UDT read optimization (`AbCipUdtReadPlanner` +
+  `AbCipUdtMemberLayout` + the `ReadGroupAsync` path in `AbCipDriver`)
+
+Unit coverage: `AbCipFetchUdtShapeTests`, `CipTemplateObjectDecoderTests`,
+`AbCipUdtMemberLayoutTests`, `AbCipUdtReadPlannerTests`,
+`AbCipDriverWholeUdtReadTests` — all with golden Template-Object byte buffers
++ offset-keyed `FakeAbCipTag` values.
+
+### 2. ALMD / ALMA alarm projection (#177)
+
+Depends on the ALMD UDT shape, which `ab_server` cannot emulate. The
+`OnAlarmEvent` raise/clear path + ack-write semantics are not exercised
+end-to-end.
+
+Unit coverage: `AbCipAlarmProjectionTests` — fakes feed `InFaulted` /
+`Severity` via `ValuesByOffset` + assert the emitted `AlarmEventArgs`.
+
+### 3. Micro800 unconnected-only path
+
+Micro800 profile `Notes`: *"ab_server has no --plc micro800 — falls back to
+controllogix emulation."*
+
+The empty routing path + unconnected-session requirement (PR 11) is unit-tested
+but never challenged at the CIP wire level. Real Micro800 (2080-series) on a
+lab rig would be the authoritative benchmark.
+
+### 4. GuardLogix safety subsystem
+
+GuardLogix profile `Notes`: *"ab_server doesn't emulate the safety
+subsystem."*
+
+Only the `_S`-suffix naming classifier (PR 12, `SecurityClassification.ViewOnly`
+forced on safety tags) runs. Actual safety-partition write rejection — what
+happens when a non-safety write lands on a real `1756-L8xS` — is not exercised.
+
+### 5. CompactLogix narrow ConnectionSize cap
+
+CompactLogix profile `Notes`: *"ab_server lacks the narrower limit itself."*
+
+Driver-side `AbCipPlcFamilyProfile` caps `ConnectionSize` at the CompactLogix
+value per PR 10, but `ab_server` accepts whatever the client asks for — the
+cap's correctness is trusted from its unit test, never stressed against a
+simulator that rejects oversized requests.
+
+### 6. BOOL-within-DINT read-modify-write (#181)
+
+The `AbCipDriver.WriteBitInDIntAsync` RMW path + its per-parent `SemaphoreSlim`
+serialization is unit-tested only (`AbCipBoolInDIntRmwTests`). `ab_server`
+seeds a plain `TestBOOL` tag; the `.N` bit-within-DINT syntax that triggers
+the RMW path is not exercised end-to-end.
+
+### 7. Capability surfaces beyond read
+
+No smoke test for:
+
+- `IWritable.WriteAsync`
+- `ITagDiscovery.DiscoverAsync` (`@tags` walker)
+- `ISubscribable.SubscribeAsync` (poll-group engine)
+- `IHostConnectivityProbe` state transitions under wire failure
+- `IPerCallHostResolver` multi-device routing
+
+The driver implements all of these + they have unit coverage, but the only
+end-to-end path `ab_server` validates today is atomic `ReadAsync`.
+
+## Logix Emulate golden-box tier
+
+Rockwell Studio 5000 Logix Emulate sits **above** ab_server in fidelity +
+**below** real hardware. When an operator has Emulate running on a
+reachable Windows box + sets two env vars, the suite promotes several
+behaviours from unit-only to end-to-end wire-level coverage:
+
+```powershell
+$env:AB_SERVER_PROFILE  = 'emulate'
+$env:AB_SERVER_ENDPOINT = '<emulate-pc-ip>:44818'
+dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests
+```
+
+With `AB_SERVER_PROFILE` unset or `abserver`, the Emulate-tier classes
+skip cleanly + the ab_server Docker fixture runs as usual.
+
+| Gap this fixture doc calls out | ab_server | Logix Emulate | Real hardware |
+|---|---|---|---|
+| UDT / CIP Template Object (task #194) | no | **yes** | yes |
+| ALMD alarm projection (task #177) | no | **yes** | yes |
+| `@tags` Symbol Object walk with `Program:` scope | partial | **yes** | yes |
+| Add-On Instructions | no | **yes** | yes |
+| GuardLogix safety-partition write rejection | no | **yes** (Emulate 5580) | yes |
+| CompactLogix narrow ConnectionSize enforcement | no | **yes** (5370 firmware) | yes |
+| EtherNet/IP embedded-switch behaviour | no | no | yes |
+| Redundant chassis failover (1756-RM) | no | no | yes |
+| Motion control timing | no | no | yes |
+
+**Tests that promote to Emulate** (gated on `AB_SERVER_PROFILE=emulate`
+via `AbServerProfileGate.SkipUnless`):
+
+- `AbCipEmulateUdtReadTests.WholeUdt_read_decodes_each_member_at_its_Template_Object_offset`
+  — #194 whole-UDT optimization, verified against real Template Object
+  bytes
+- `AbCipEmulateAlmdTests.Real_ALMD_raise_fires_OnAlarmEvent_through_the_driver_projection`
+  — #177 ALMD projection, verified against the real ALMD instruction
+
+**Required Studio 5000 project state** is documented in
+[`tests/…/AbCip.IntegrationTests/LogixProject/README.md`](../../tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/LogixProject/README.md);
+the `.L5X` export lands there once the Emulate PC is on-site + the
+project is authored.
+
+**Costs to accept**:
+
+- **Rockwell TechConnect or per-seat license** — not redistributable;
+  not CI-runnable. Each operator licenses their own Emulate install.
+- **Windows-only + Hyper-V conflict** — Emulate can't coexist with
+  Docker Desktop's WSL 2 backend on the same OS, same way TwinCAT XAR
+  can't (see `docs/v2/dev-environment.md` §Integration host).
+- **Manual lifecycle** — no `docker compose up` equivalent; operator
+  opens Emulate, loads the L5X, clicks Run. The L5X in the repo keeps
+  project state reproducible, runtime-start is human.
+
+## When to trust ab_server, when to reach for a rig
+
+| Question | ab_server | Unit tests | Logix Emulate | Lab rig |
+| --- | --- | --- | --- | --- |
+| "Does the driver talk CIP at all?" | yes | - | yes | - |
+| "Is my atomic read path wired correctly?" | yes | yes | yes | yes |
+| "Does whole-UDT grouping work?" | no | yes | **yes** | yes |
+| "Do ALMD alarms raise + clear?" | no | yes | **yes** | yes |
+| "Is Micro800 unconnected-only enforced wire-side?" | no (emulated as CLX) | partial | yes | yes (required) |
+| "Does GuardLogix reject non-safety writes on safety tags?" | no | no | yes (Emulate 5580) | yes |
+| "Does CompactLogix refuse oversized ConnectionSize?" | no | partial | yes (5370 firmware) | yes |
+| "Does BOOL-in-DINT RMW race against concurrent writers?" | no | yes | partial | yes (stress) |
+| "Does EtherNet/IP embedded-switch behave correctly?" | no | no | no | yes (required) |
+| "Does redundant-chassis failover work?" | no | no | no | yes (required) |
+
+## Follow-up candidates
+
+If integration-level UDT / alarm / quirk proof becomes a shipping gate, the
+options are roughly:
+
+1. **Logix Emulate golden-box tier** (scaffolded; see the section above) —
+   highest-fidelity path short of real hardware. Closes UDT / ALMD / AOI /
+   optimized-DB gaps in one license + one Windows PC.
+2. **Extend `ab_server`** upstream — the project accepts PRs + already
+   carries a CIP framing layer that UDT emulation could plug into.
+3. **Stand up a lab rig** — physical `1756-L7x` / `5069-L3x` / `2080-LC30`
+   / `1756-L8xS` controllers. The only path that covers safety partitions
+   across nodes, redundant chassis, embedded-switch behaviour, and motion
+   timing.
+
+See also:
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbServerFixture.cs`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbServerProfile.cs`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbServerProfileGate.cs`
+  — `AB_SERVER_PROFILE` tier gate
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbCipReadSmokeTests.cs`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/` — ab_server
+  image + compose
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Emulate/` — Logix
+  Emulate tier tests
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/LogixProject/README.md`
+  — L5X project state the Emulate tier expects
+- `docs/v2/test-data-sources.md` §2 — the broader test-data-source picking
+  rationale this fixture slots into

docs/drivers/FOCAS-Test-Fixture.md

@@ -0,0 +1,115 @@
+# FOCAS test fixture
+
+Coverage map + gap inventory for the FANUC FOCAS2 CNC driver.
+
+**TL;DR: there is no integration fixture.** Every test uses a
+`FakeFocasClient` injected via `IFocasClientFactory`. Fanuc's FOCAS library
+(`Fwlib32.dll`) is closed-source proprietary with no public simulator;
+CNC-side behavior is trusted from field deployments.
+
+## What the fixture is
+
+Nothing at the integration layer.
+`tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/` is unit-only. The driver ships
+as Tier C (process-isolated) per `docs/v2/driver-stability.md` because the
+FANUC DLL has known crash modes; tests can't replicate those in-process.
+
+## What it actually covers (unit only)
+
+- `FocasCapabilityTests` — data-type mapping (PMC bit / word / float,
+  macro variable types, parameter types)
+- `FocasCapabilityMatrixTests` — per-CNC-series range validation (macro
+  / parameter / PMC letter + number) across 16i / 0i-D / 0i-F /
+  30i / PowerMotion. See [`docs/v2/focas-version-matrix.md`](../v2/focas-version-matrix.md)
+  for the authoritative matrix. 46 theory cases lock every documented
+  range boundary — widening a range without updating the doc fails a
+  test.
+- `FocasReadWriteTests` — read + write against the fake, FOCAS native status
+  → OPC UA StatusCode mapping
+- `FocasScaffoldingTests` — `IDriver` lifecycle + multi-device routing
+- `FocasPmcBitRmwTests` — PMC bit read-modify-write synchronization (per-byte
+  `SemaphoreSlim`, mirrors the AB / Modbus pattern from #181)
+- `FwlibNativeHelperTests` — `Focas32.dll` → `Fwlib32.dll` bridge validation
+  + P/Invoke signature validation
+
+Capability surfaces whose contract is verified: `IDriver`, `IReadable`,
+`IWritable`, `ITagDiscovery`, `ISubscribable`, `IHostConnectivityProbe`,
+`IPerCallHostResolver`.
+
+Pre-flight validation runs in `FocasDriver.InitializeAsync` — configs
+referencing out-of-range addresses fail at load time with a diagnostic
+message naming the CNC series + documented limit. This closes the
+cheap half of the hardware-free stability gap; Tier-C process
+isolation (task #220) closes the expensive half — see
+[`docs/v2/implementation/focas-isolation-plan.md`](../v2/implementation/focas-isolation-plan.md).
+
+## What it does NOT cover
+
+### 1. FOCAS wire traffic
+
+No FOCAS TCP frame is sent. `Fwlib32.dll`'s TCP-to-FANUC-gateway exchange is
+closed-source; the driver trusts the P/Invoke layer per #193. Real CNC
+correctness is trusted from field deployments.
+
+### 2. Alarm / parameter-change callbacks
+
+FOCAS has no push model — the driver polls via the shared `PollGroupEngine`.
+There are no CNC-initiated callbacks to test; the absence is by design.
+
+### 3. Macro / ladder variable types
+
+FANUC has CNC-specific extensions (macro variables `#100-#999`, system
+variables `#1000-#5000`, PMC timers / counters / keep-relays) whose
+per-address semantics differ across 0i-F / 30i / 31i / 32i Series. Driver
+covers the common address shapes; per-model quirks are not stressed.
+
+### 4. Model-specific behavior
+
+- Alarm retention across power cycles (model-specific CNC behavior)
+- Parameter range enforcement (CNC rejects out-of-range writes)
+- MTB (machine tool builder) custom screens that expose non-standard data
+
+### 5. Tier-C process isolation behavior
+
+Per driver-stability.md, FOCAS should run process-isolated because
+`Fwlib32.dll` has documented crash modes. The test suite runs in-process +
+only exercises the happy path + mapped error codes — a native access
+violation from the DLL would take the test host down. The process-isolation
+path (similar to Galaxy's out-of-process Host) has been scoped but not
+implemented.
+
+## When to trust FOCAS tests, when to reach for a rig
+
+| Question | Unit tests | Real CNC |
+| --- | --- | --- |
+| "Does PMC address `R100.3` route to the right bit?" | yes | yes |
+| "Does the FANUC status → OPC UA StatusCode map cover every documented code?" | yes (contract) | yes |
+| "Does a real read against a 30i Series return correct bytes?" | no | yes (required) |
+| "Does `Fwlib32.dll` crash on concurrent reads?" | no | yes (stress) |
+| "Do macro variables round-trip across power cycles?" | no | yes (required) |
+
+## Follow-up candidates
+
+1. **Nothing public** — Fanuc's FOCAS Developer Kit ships an emulator DLL
+   but it's under NDA + tied to licensed dev-kit installations; can't
+   redistribute for CI.
+2. **Lab rig** — used FANUC 0i-F simulator controller (or a retired machine
+   tool) on a dedicated network; only path that covers real CNC behavior.
+3. **Process isolation first** — before trusting FOCAS in production at
+   scale, shipping the Tier-C out-of-process Host architecture (similar to
+   Galaxy) is higher value than a CI simulator.
+
+## Key fixture / config files
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FakeFocasClient.cs` —
+  in-process fake implementing `IFocasClient`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasCapabilityMatrixTests.cs`
+  — parameterized theories locking the per-series matrix
+- `src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs` — ctor takes
+  `IFocasClientFactory`
+- `src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCapabilityMatrix.cs` —
+  per-CNC-series range validator (the matrix the doc describes)
+- `docs/v2/focas-version-matrix.md` — authoritative range reference
+- `docs/v2/implementation/focas-isolation-plan.md` — Tier-C isolation
+  plan (task #220)
+- `docs/v2/driver-stability.md` — Tier C scope + process-isolation rationale

docs/drivers/Galaxy-Test-Fixture.md

@@ -0,0 +1,164 @@
+# Galaxy test fixture
+
+Coverage map + gap inventory for the Galaxy driver — out-of-process Host
+(net48 x86 MXAccess COM) + Proxy (net10) + Shared protocol.
+
+**TL;DR: Galaxy has the richest test harness in the fleet** — real Host
+subprocess spawn, real ZB SQL queries, IPC parity checks against the v1
+LmxProxy reference, + live-smoke tests when MXAccess runtime is actually
+installed. Gaps are live-plant + failover-shaped: the E2E suite covers the
+representative ~50-tag deployment but not large-site discovery stress, real
+Rockwell/Siemens PLC enumeration through MXAccess, or ZB SQL Always-On
+replica failover.
+
+## What the fixture is
+
+Multi-project test topology:
+
+- **E2E parity** —
+  `tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.E2E/ParityFixture.cs` spawns the
+  production `OtOpcUa.Driver.Galaxy.Host.exe` as a subprocess, opens the
+  named-pipe IPC, connects `GalaxyProxyDriver` + runs hierarchy / stability
+  parity tests against both.
+- **Host.Tests** —
+  `tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/` — direct Host process
+  testing (18+ test classes covering alarm discovery, AVEVA prerequisite
+  checks, IPC dispatcher, alarm tracker, probe manager, historian
+  cluster/quality/wiring, history read, OPC UA attribute mapping,
+  subscription lifecycle, reconnect, multi-host proxy, ADS address routing,
+  expression evaluation) + `GalaxyRepositoryLiveSmokeTests` that hit real
+  ZB SQL.
+- **Proxy.Tests** — `GalaxyProxyDriver` client contract tests.
+- **Shared.Tests** — shared protocol + address model.
+- **TestSupport** — test helpers reused across the above.
+
+## How tests skip
+
+- **E2E parity**: `ParityFixture.SkipIfUnavailable()` runs at class init and
+  checks Windows-only, non-admin user, ZB SQL reachable on
+  `localhost:1433`, Host EXE built in the expected `bin/` folder. Any miss
+  → tests skip.
+- **Live-smoke** (`GalaxyRepositoryLiveSmokeTests`): `Assert.Skip` when ZB
+  unreachable. A `per project_galaxy_host_installed` memory on this repo's
+  dev box notes the MXAccess runtime is installed + pipe ACL denies Admins,
+  so live tests must run from a non-elevated shell.
+- **Unit** tests (Shared, Proxy contract, most Host.Tests) have no skip —
+  they run anywhere.
+
+## What it actually covers
+
+### E2E parity suite
+
+- `HierarchyParityTests` — Host address-space hierarchy vs v1 LmxProxy
+  reference (same ZB, same Galaxy, same shape)
+- `StabilityFindingsRegressionTests` — probe subscription failure
+  handling + host-status mutation guard from the v1 stability findings
+  backlog
+
+### Host.Tests (representative)
+
+- Alarm discovery → subsystem setup
+- AVEVA prerequisite checks (runtime installed, platform deployed, etc.)
+- IPC dispatcher — request/response routing over the named pipe
+- Alarm tracker state machine
+- Probe manager — per-runtime probe subscription + reconnect
+- Historian cluster / quality / wiring — Aveva Historian integration
+- OPC UA attribute mapping
+- Subscription lifecycle + reconnect
+- Multi-host proxy routing
+- ADS address routing + expression evaluation (Galaxy's legacy expression
+  language)
+
+### Live-smoke
+
+- `GalaxyRepositoryLiveSmokeTests` — real SQL against ZB database, verifies
+  the ZB schema + `LocalPlatform` scope filter + change-detection query
+  shape match production.
+
+### Capability surfaces hit
+
+All of them: `IDriver`, `IReadable`, `IWritable`, `ITagDiscovery`,
+`ISubscribable`, `IHostConnectivityProbe`, `IPerCallHostResolver`,
+`IAlarmSource`, `IHistoryProvider`. Galaxy is the only driver where every
+interface sees both contract + real-integration coverage.
+
+## What it does NOT cover
+
+### 1. MXAccess COM by default
+
+The E2E parity suite backs subscriptions via the DB-only path; MXAccess COM
+integration opts in via a separate live-smoke. So "does the MXAccess STA
+pump correctly handle real Wonderware runtime events" is exercised only
+when the operator runs live smoke on a machine with MXAccess installed.
+
+### 2. Real Rockwell / Siemens PLC enumeration
+
+Galaxy runtime talks to PLCs through MXAccess (Device Integration Objects).
+The CI parity suite uses a representative ~50-tag deployment; large sites
+(1000+ tag hierarchies, multi-Galaxy replication, deeply-nested templates)
+are not stressed.
+
+### 3. ZB SQL Always-On failover
+
+Live-smoke hits a single SQL instance. Real production ZB often runs on
+Always-On availability groups; replica failover behavior is not tested.
+
+### 4. Galaxy replication / backup-restore
+
+Galaxy supports backup + partial replication across platforms — these
+rewrite the ZB schema in ways that change the contained_name vs tag_name
+mapping. Not exercised.
+
+### 5. Historian failover
+
+Aveva Historian can be clustered. `historian cluster / quality` tests
+verify the cluster-config query; they don't exercise actual failover
+(primary dies → secondary takes over mid-HistoryRead).
+
+### 6. AVEVA runtime version matrix
+
+MXAccess COM contract varies subtly across System Platform 2017 / 2020 /
+2023. The live-smoke runs against whatever version is installed on the dev
+box; CI has no AVEVA installed at all (licensing + footprint).
+
+## When to trust the Galaxy suite, when to reach for a live plant
+
+| Question | E2E parity | Live-smoke | Real plant |
+| --- | --- | --- | --- |
+| "Does Host spawn + IPC round-trip work?" | yes | yes | yes |
+| "Does the ZB schema query match production shape?" | partial | yes | yes |
+| "Does MXAccess COM handle runtime reconnect correctly?" | no | yes | yes |
+| "Does the driver scale to 1000+ tags on one Galaxy?" | no | partial | yes (required) |
+| "Does historian failover mid-read return a clean error?" | no | no | yes (required) |
+| "Does System Platform 2023's MXAccess differ from 2020?" | no | partial | yes (required) |
+| "Does ZB Always-On replica failover preserve generation?" | no | no | yes (required) |
+
+## Follow-up candidates
+
+1. **System Platform 2023 live-smoke matrix** — set up a second dev box
+   running SP2023; run the same live-smoke against both to catch COM-contract
+   drift early.
+2. **Synthetic large-site fixture** — script a ZB populator that creates a
+   1000-Equipment / 20000-tag hierarchy, run the parity suite against it.
+   Catches O(N) → O(N²) discovery regressions.
+3. **Historian failover scripted test** — with a two-node AVEVA Historian
+   cluster, tear down primary mid-HistoryRead + verify the driver's failover
+   behavior + error surface.
+4. **ZB Always-On CI** — SQL Server 2022 on Linux supports Always-On;
+   could stand up a two-replica group for replica-failover coverage.
+
+This is already the best-tested driver; the remaining work is site-scale
++ production-topology coverage, not capability coverage.
+
+## Key fixture / config files
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.E2E/ParityFixture.cs` — E2E fixture
+  that spawns Host + connects Proxy
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/GalaxyRepositoryLiveSmokeTests.cs`
+  — live ZB smoke with `Assert.Skip` gate
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.TestSupport/` — shared helpers
+- `docs/drivers/Galaxy.md` — COM bridge + STA pump + IPC architecture
+- `docs/drivers/Galaxy-Repository.md` — ZB SQL reader + `LocalPlatform`
+  scope filter + change detection
+- `docs/v2/aveva-system-platform-io-research.md` — MXAccess + Wonderware
+  background

docs/drivers/Modbus-Test-Fixture.md

@@ -0,0 +1,117 @@
+# Modbus test fixture
+
+Coverage map + gap inventory for the Modbus TCP driver's integration-test
+harness backed by `pymodbus` simulator profiles per PLC family.
+
+**TL;DR:** Modbus is the best-covered driver — a real `pymodbus` server on
+localhost with per-family seed-register profiles, plus a skip-gate when the
+simulator port isn't reachable. Covers DL205 / Mitsubishi MELSEC / Siemens
+S7-1500 family quirks end-to-end. Gaps are mostly error-path + alarm/history
+shaped (neither is a Modbus-side concept).
+
+## What the fixture is
+
+- **Simulator**: `pymodbus` (Python, BSD) launched as a pinned Docker
+  container at
+  `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/`.
+  Docker is the only supported launch path.
+- **Lifecycle**: `ModbusSimulatorFixture` (collection-scoped) TCP-probes
+  `localhost:5020` on first use. `MODBUS_SIM_ENDPOINT` env var overrides the
+  endpoint so the same suite can target a real PLC.
+- **Profiles**: `DL205Profile`, `MitsubishiProfile`, `S7_1500Profile` —
+  each composes device-specific register-format + quirk-seed JSON for pymodbus.
+  Profile JSONs live under `Docker/profiles/` and are baked into the image.
+- **Compose services**: one per profile (`standard` / `dl205` /
+  `mitsubishi` / `s7_1500`); only one binds `:5020` at a time.
+- **Tests skip** via `Assert.Skip(sim.SkipReason)` when the probe fails; no
+  custom FactAttribute needed because `ModbusSimulatorCollection` carries the
+  skip reason.
+
+## What it actually covers
+
+### DL205 (Automation Direct)
+
+- `DL205SmokeTests` — FC16 write → FC03 read round-trip on holding register
+- `DL205CoilMappingTests` — Y-output / C-relay / X-input address mapping
+  (octal → Modbus offset)
+- `DL205ExceptionCodeTests` — Modbus exception → OPC UA StatusCode mapping
+- `DL205FloatCdabQuirkTests` — CDAB word-swap float encoding
+- `DL205StringQuirkTests` — packed-string V-memory layout
+- `DL205VMemoryQuirkTests` — V-memory octal addressing
+- `DL205XInputTests` — X-register read-only enforcement
+
+### Mitsubishi MELSEC
+
+- `MitsubishiSmokeTests` — read + write round-trip
+- `MitsubishiQuirkTests` — word-order, device-code mapping (D/M/X/Y ranges)
+
+### Siemens S7-1500 (Modbus gateway flavor)
+
+- `S7_1500SmokeTests` — read + write round-trip
+- `S7_ByteOrderTests` — ABCD/DCBA/BADC/CDAB byte-order matrix
+
+### Capability surfaces hit
+
+- `IReadable` + `IWritable` — full round-trip
+- `ISubscribable` — via the shared `PollGroupEngine` (polled subscription)
+- `IHostConnectivityProbe` — TCP-reach transitions
+
+## What it does NOT cover
+
+### 1. No `ITagDiscovery`
+
+Modbus has no symbol table — the driver requires a static tag map from
+`DriverConfig`. There is no discovery path to test + none in the fixture.
+
+### 2. Error-path fuzzing
+
+`pymodbus` serves the seeded values happily; the fixture can't easily inject
+exception responses (code 0x01–0x0B) or malformed PDUs. The
+`AbCipStatusMapper`-equivalent for exception codes is unit-tested via
+`DL205ExceptionCodeTests` but the simulator itself never refuses a read.
+
+### 3. Variant-specific quirks beyond the three profiles
+
+- FX5U / QJ71MT91 Mitsubishi variants — profile scaffolds exist, no tests yet
+- Non-S7-1500 Siemens (S7-1200 / ET200SP) — byte-order covered but
+  connection-pool + fragmentation quirks untested
+- DL205-family cousins (DL06, DL260) — no dedicated profile
+
+### 4. Subscription stress
+
+`PollGroupEngine` is unit-tested standalone but the simulator doesn't exercise
+it under multi-register packing stress (FC03 with 125-register batches,
+boundary splits, etc.).
+
+### 5. Alarms / history
+
+Not a Modbus concept. Driver doesn't implement `IAlarmSource` or
+`IHistoryProvider`; no test coverage is the correct shape.
+
+## When to trust the Modbus fixture, when to reach for a rig
+
+| Question | Fixture | Unit tests | Real PLC |
+| --- | --- | --- | --- |
+| "Does FC03/FC06/FC16 work end-to-end?" | yes | - | yes |
+| "Does DL205 octal addressing map correctly?" | yes | yes | yes |
+| "Does float CDAB word-swap round-trip?" | yes | yes | yes |
+| "Does the driver handle exception responses?" | no | yes | yes (required) |
+| "Does packing 125 regs into one FC03 work?" | no | no | yes (required) |
+| "Does FX5U behave like Q-series?" | no | no | yes (required) |
+
+## Follow-up candidates
+
+1. Add `MODBUS_SIM_ENDPOINT` override documentation to
+   `docs/v2/test-data-sources.md` so operators can point the suite at a lab rig.
+2. Extend `pymodbus` profiles to inject exception responses — a JSON flag per
+   register saying "next read returns exception 0x04."
+3. Add an FX5U profile once a lab rig is available; the scaffolding is in place.
+
+## Key fixture / config files
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/ModbusSimulatorFixture.cs`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/DL205/DL205Profile.cs`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Mitsubishi/MitsubishiProfile.cs`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/S7/S7_1500Profile.cs`
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/` —
+  Dockerfile + compose + per-family JSON profiles

docs/drivers/OpcUaClient-Test-Fixture.md

@@ -0,0 +1,170 @@
+# OPC UA Client test fixture
+
+Coverage map + gap inventory for the OPC UA Client (gateway / aggregation)
+driver.
+
+**TL;DR:** Wire-level coverage now exists via
+[opc-plc](https://github.com/Azure-Samples/iot-edge-opc-plc) — Microsoft
+Industrial IoT's OPC UA PLC simulator running in Docker (task #215). Real
+Secure Channel, real Session, real MonitoredItem exchange against an
+independent server implementation. Unit tests still carry the exhaustive
+capability matrix (cert auth / security policies / reconnect / failover /
+attribute mapping). Gaps remaining: upstream-server-specific quirks
+(historian aggregates, typed ConditionType events, SDK-publish-queue edge
+behavior under load) — opc-plc uses the same OPCFoundation stack internally
+so fully-independent-stack coverage needs `open62541/open62541` as a second
+image (follow-up).
+
+## What the fixture is
+
+**Integration layer** (task #215):
+`tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests/` stands up
+`mcr.microsoft.com/iotedge/opc-plc:2.14.10` via `Docker/docker-compose.yml`
+on `opc.tcp://localhost:50000`. `OpcPlcFixture` probes the port at
+collection init + skips tests with a clear message when the container's
+not running (matches the Modbus/pymodbus + S7/python-snap7 skip pattern).
+Docker is the launcher — no PowerShell wrapper needed because opc-plc
+ships pre-containerized. Compose-file flags: `--ut` (unsecured transport
+advertised), `--aa` (auto-accept client certs — opc-plc's cert trust store
+resets on each spin-up), `--alm` (alarm simulation for IAlarmSource
+follow-up coverage), `--pn=50000` (port).
+
+**Unit layer**:
+`tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/` is still the primary
+coverage. Tests inject fakes through the driver's construction path; the
+OPCFoundation.NetStandard `Session` surface is wrapped behind an interface
+the tests mock.
+
+## What it actually covers
+
+### Integration (opc-plc Docker, task #215)
+
+- `OpcUaClientSmokeTests.Client_connects_and_reads_StepUp_node_through_real_OPC_UA_stack` —
+  full Secure Channel + Session + `ns=3;s=StepUp` Read round-trip
+- `OpcUaClientSmokeTests.Client_reads_batch_of_varied_types_from_live_simulator` —
+  batch Read of UInt32 / Int32 / Boolean; asserts `bool`-specific Variant
+  decoding to catch a common attribute-mapping regression
+- `OpcUaClientSmokeTests.Client_subscribe_receives_StepUp_data_changes_from_live_server` —
+  real `MonitoredItem` subscription against `ns=3;s=FastUInt1` (ticks every
+  100 ms); asserts `OnDataChange` fires within 3 s of subscribe
+
+Wire-level surfaces verified: `IDriver` + `IReadable` + `ISubscribable` +
+`IHostConnectivityProbe` (via the Secure Channel exchange).
+
+### Unit
+
+The surface is broad because `OpcUaClientDriver` is the richest-capability
+driver in the fleet (it's a gateway for another OPC UA server, so it
+mirrors the full capability matrix):
+
+- `OpcUaClientDriverScaffoldTests` — `IDriver` lifecycle
+- `OpcUaClientReadWriteTests` — read + write lifecycle
+- `OpcUaClientSubscribeAndProbeTests` — monitored-item subscription + probe
+  state transitions
+- `OpcUaClientDiscoveryTests` — `GetEndpoints` + endpoint selection
+- `OpcUaClientAttributeMappingTests` — OPC UA node attribute → driver value
+  mapping
+- `OpcUaClientSecurityPolicyTests` — `SignAndEncrypt` / `Sign` / `None`
+  policy negotiation contract
+- `OpcUaClientCertAuthTests` — cert store paths, revocation-list config
+- `OpcUaClientReconnectTests` — SDK reconnect hook + `TransferSubscriptions`
+  across the disconnect boundary
+- `OpcUaClientFailoverTests` — primary → secondary session fallback per
+  driver config
+- `OpcUaClientAlarmTests` — A&E severity bucket (1–1000 → Low / Medium /
+  High / Critical), subscribe / unsubscribe / ack contract
+- `OpcUaClientHistoryTests` — historical data read + interpolation contract
+
+Capability surfaces whose contract is verified: `IDriver`, `ITagDiscovery`,
+`IReadable`, `IWritable`, `ISubscribable`, `IHostConnectivityProbe`,
+`IAlarmSource`, `IHistoryProvider`.
+
+## What it does NOT cover
+
+### 1. Real stack exchange
+
+No UA Secure Channel is ever opened. Every test mocks `Session.ReadAsync`,
+`Session.CreateSubscription`, `Session.AddItem`, etc. — the SDK itself is
+trusted. Certificate validation, signing, nonce handling, chunk assembly,
+keep-alive cadence — all SDK-internal and untested here.
+
+### 2. Subscription transfer across reconnect
+
+Contract test: "after a simulated reconnect, `TransferSubscriptions` is
+called with the right handles." Real behavior: SDK re-publishes against the
+new channel and some events can be lost depending on publish-queue state.
+The lossy window is not characterized.
+
+### 3. Large-scale subscription stress
+
+100+ monitored items with heterogeneous publish intervals under a single
+session — the shape that breaks publish-queue-size tuning in the wild — is
+not exercised.
+
+### 4. Real historian mappings
+
+`IHistoryProvider.ReadRawAsync` + `ReadProcessedAsync` +
+`ReadAtTimeAsync` + `ReadEventsAsync` are contract-mocked. Against a real
+historian (AVEVA Historian, Prosys historian, Kepware LocalHistorian) each
+has specific interpolation + bad-quality-handling quirks the contract test
+doesn't see.
+
+### 5. Real A&E events
+
+Alarm subscription is mocked via filtered monitored items; the actual
+`EventFilter` select-clause behavior against a server that exposes typed
+ConditionType events (non-base `BaseEventType`) is not verified.
+
+### 6. Authentication variants
+
+- Anonymous, UserName/Password, X509 cert tokens — each is contract-tested
+  but not exchanged against a server that actually enforces each.
+- LDAP-backed `UserName` (matching this repo's server-side
+  `LdapUserAuthenticator`) requires a live LDAP round-trip; not tested.
+
+## When to trust OpcUaClient tests, when to reach for a server
+
+| Question | Unit tests | Real upstream server |
+| --- | --- | --- |
+| "Does severity 750 bucket as High?" | yes | yes |
+| "Does the driver call `TransferSubscriptions` after reconnect?" | yes | yes |
+| "Does a real OPC UA read/write round-trip work?" | no | yes (required) |
+| "Does event-filter-based alarm subscription return ConditionType events?" | no | yes (required) |
+| "Does history read from AVEVA Historian return correct aggregates?" | no | yes (required) |
+| "Does the SDK's publish queue lose notifications under load?" | no | yes (stress) |
+
+## Follow-up candidates
+
+The easiest win here is to **wire the client driver tests against this
+repo's own server**. The integration test project
+`tests/ZB.MOM.WW.OtOpcUa.Server.Tests/OpcUaServerIntegrationTests.cs`
+already stands up a real OPC UA server on a non-default port with a seeded
+FakeDriver. An `OpcUaClientLiveLoopbackTests` that connects the client
+driver to that server would give:
+
+- Real Secure Channel negotiation
+- Real Session / Subscription / MonitoredItem exchange
+- Real read/write round-trip
+- Real certificate validation (the integration test already sets up PKI)
+
+It wouldn't cover upstream-server-specific quirks (AVEVA Historian, Kepware,
+Prosys), but it would cover 80% of the SDK surface the driver sits on top
+of.
+
+Beyond that:
+
+1. **Prosys OPC UA Simulation Server** — free, Windows-available, scriptable.
+2. **UaExpert Server-Side Simulator** — Unified Automation's sample server;
+   good coverage of typed ConditionType events.
+3. **Dedicated historian integration lab** — only path for
+   historian-specific coverage.
+
+## Key fixture / config files
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/` — unit tests with
+  mocked `Session`
+- `src/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/OpcUaClientDriver.cs` — ctor +
+  session-factory seam tests mock through
+- `tests/ZB.MOM.WW.OtOpcUa.Server.Tests/OpcUaServerIntegrationTests.cs` —
+  the server-side integration harness a future loopback client test could
+  piggyback on

docs/drivers/README.md

@@ -37,6 +37,19 @@ Driver type metadata is registered at startup in `DriverTypeRegistry` (`src/ZB.M
 
 - **All other drivers** share a single per-driver specification in [docs/v2/driver-specs.md](../v2/driver-specs.md) — addressing, data-type maps, connection settings, and quirks live there. That file is the authoritative per-driver reference; this index points at it rather than duplicating.
 
+## Test-fixture coverage maps
+
+Each driver has a dedicated fixture doc that lays out what the integration / unit harness actually covers vs. what's trusted from field deployments. Read the relevant one before claiming "green suite = production-ready" for a driver.
+
+- [AB CIP](AbServer-Test-Fixture.md) — Dockerized `ab_server` (multi-stage build from libplctag source); atomic-read smoke across 4 families; UDT / ALMD / family quirks unit-only
+- [Modbus](Modbus-Test-Fixture.md) — Dockerized `pymodbus` + per-family JSON profiles (4 compose profiles); best-covered driver, gaps are error-path-shaped
+- [Siemens S7](S7-Test-Fixture.md) — Dockerized `python-snap7` server; DB/MB read + write round-trip verified end-to-end on `:1102`
+- [AB Legacy](AbLegacy-Test-Fixture.md) — Docker scaffold via `ab_server` PCCC mode (task #224); wire-level round-trip currently blocked by ab_server's PCCC coverage gap, docs call out RSEmulate 500 + lab-rig resolution paths
+- [TwinCAT](TwinCAT-Test-Fixture.md) — XAR-VM integration scaffolding (task #221); three smoke tests skip when VM unreachable. Unit via `FakeTwinCATClient` with native-notification harness
+- [FOCAS](FOCAS-Test-Fixture.md) — no integration fixture, unit-only via `FakeFocasClient`; Tier C out-of-process isolation scoped but not shipped
+- [OPC UA Client](OpcUaClient-Test-Fixture.md) — no integration fixture, unit-only via mocked `Session`; loopback against this repo's own server is the obvious next step
+- [Galaxy](Galaxy-Test-Fixture.md) — richest harness: E2E Host subprocess + ZB SQL live-smoke + MXAccess opt-in
+
 ## Related cross-driver docs
 
 - [HistoricalDataAccess.md](../HistoricalDataAccess.md) — `IHistoryProvider` dispatch, aggregate mapping, continuation points. The Galaxy driver's Aveva Historian implementation is the first; OPC UA Client forwards to the upstream server; other drivers do not implement the interface and return `BadHistoryOperationUnsupported`.

docs/drivers/S7-Test-Fixture.md

@@ -0,0 +1,121 @@
+# Siemens S7 test fixture
+
+Coverage map + gap inventory for the S7 driver.
+
+**TL;DR:** S7 now has a wire-level integration fixture backed by
+[python-snap7](https://github.com/gijzelaerr/python-snap7)'s `Server` class
+(task #216). Atomic reads (u16 / i16 / i32 / f32 / bool-with-bit) + DB
+write-then-read round-trip are exercised end-to-end through S7netplus +
+real ISO-on-TCP on `localhost:1102`. Unit tests still carry everything
+else (address parsing, error-branch handling, probe-loop contract). Gaps
+remaining are variant-quirk-shaped: Optimized-DB symbolic access, PG/OP
+session types, PUT/GET-disabled enforcement — all need real hardware.
+
+## What the fixture is
+
+**Integration layer** (task #216):
+`tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/` stands up a
+python-snap7 `Server` via `Docker/docker-compose.yml --profile s7_1500`
+on `localhost:1102` (pinned `python:3.12-slim-bookworm` base +
+`python-snap7>=2.0`). Docker is the only supported launch path.
+`Snap7ServerFixture` probes the port at collection init + skips with a
+clear message when unreachable (matches the pymodbus pattern).
+`server.py` (baked into the image under `Docker/`) reads a JSON profile
++ seeds DB/MB bytes at declared offsets; seeds are typed (`u16` / `i16`
+/ `i32` / `f32` / `bool` / `ascii` for S7 STRING).
+
+**Unit layer**: `tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/` covers
+everything the wire-level suite doesn't — address parsing, error
+branches, probe-loop contract. All tests tagged
+`[Trait("Category", "Unit")]`.
+
+The driver ctor change that made this possible:
+`Plc(CpuType, host, port, rack, slot)` — S7netplus 0.20's 5-arg overload
+— wires `S7DriverOptions.Port` through so the simulator can bind 1102
+(non-privileged) instead of 102 (root / Firewall-prompt territory).
+
+## What it actually covers
+
+### Integration (python-snap7, task #216)
+
+- `S7_1500SmokeTests.Driver_reads_seeded_u16_through_real_S7comm` — DB1.DBW0
+  read via real S7netplus over TCP + simulator; proves handshake + read path
+- `S7_1500SmokeTests.Driver_reads_seeded_typed_batch` — i16, i32, f32,
+  bool-with-bit in one batch call; proves typed decode per S7DataType
+- `S7_1500SmokeTests.Driver_write_then_read_round_trip_on_scratch_word` —
+  `DB1.DBW100` write → read-back; proves write path + buffer visibility
+
+### Unit
+
+- `S7AddressParserTests` — S7 address syntax (`DB1.DBD0`, `M10.3`, `IW4`, etc.)
+- `S7DriverScaffoldTests` — `IDriver` lifecycle (init / reinit / shutdown / health)
+- `S7DriverReadWriteTests` — error paths (uninitialized read/write, bad
+  addresses, transport exceptions)
+- `S7DiscoveryAndSubscribeTests` — `ITagDiscovery.DiscoverAsync` + polled
+  `ISubscribable` contract with the shared `PollGroupEngine`
+
+Capability surfaces whose contract is verified: `IDriver`, `ITagDiscovery`,
+`IReadable`, `IWritable`, `ISubscribable`, `IHostConnectivityProbe`.
+Wire-level surfaces verified: `IReadable`, `IWritable`.
+
+## What it does NOT cover
+
+### 1. Wire-level anything
+
+No ISO-on-TCP frame is ever sent during the test suite. S7netplus is the only
+wire-path abstraction and it has no in-process fake mode; the shipping choice
+was to contract-test via `IS7Client` rather than patch into S7netplus
+internals.
+
+### 2. Read/write happy path
+
+Every `S7DriverReadWriteTests` case exercises error branches. A successful
+read returning real PLC data is not tested end-to-end — the return value is
+whatever the fake says it is.
+
+### 3. Mailbox serialization under concurrent reads
+
+The driver's `SemaphoreSlim` serializes S7netplus calls because the S7 CPU's
+comm mailbox is scanned at most once per cycle. Contention behavior under
+real PLC latency is not exercised.
+
+### 4. Variant quirks
+
+S7-1200 vs S7-1500 vs S7-300/400 connection semantics (PG vs OP vs S7-Basic)
+not differentiated at test time.
+
+### 5. Data types beyond the scalars
+
+UDT fan-out, `STRING` with length-prefix quirks, `DTL` / `DATE_AND_TIME`,
+arrays of structs — not covered.
+
+## When to trust the S7 tests, when to reach for a rig
+
+| Question | Unit tests | Real PLC |
+| --- | --- | --- |
+| "Does the address parser accept X syntax?" | yes | - |
+| "Does the driver lifecycle hang / crash?" | yes | yes |
+| "Does a real read against an S7-1500 return correct bytes?" | no | yes (required) |
+| "Does mailbox serialization actually prevent PG timeouts?" | no | yes (required) |
+| "Does a UDT fan-out produce usable member variables?" | no | yes (required) |
+
+## Follow-up candidates
+
+1. **Snap7 server** — [Snap7](https://snap7.sourceforge.net/) ships a
+   C-library-based S7 server that could run in-CI on Linux. A pinned build +
+   a fixture shape similar to `ab_server` would give S7 parity with Modbus /
+   AB CIP coverage.
+2. **Plcsim Advanced** — Siemens' paid emulator. Licensed per-seat; fits a
+   lab rig but not CI.
+3. **Real S7 lab rig** — cheapest physical PLC (CPU 1212C) on a dedicated
+   network port, wired via self-hosted runner.
+
+Without any of these, S7 driver correctness against real hardware is trusted
+from field deployments, not from the test suite.
+
+## Key fixture / config files
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/` — unit tests only, no harness
+- `src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs` — ctor takes
+  `IS7ClientFactory` which tests fake; docstring lines 8-20 note the deferred
+  integration fixture

docs/drivers/TwinCAT-Test-Fixture.md

@@ -0,0 +1,158 @@
+# TwinCAT test fixture
+
+Coverage map + gap inventory for the Beckhoff TwinCAT ADS driver.
+
+**TL;DR:** Integration-test scaffolding lives at
+`tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests/` (task #221).
+`TwinCATXarFixture` probes TCP 48898 on an operator-supplied VM; three
+smoke tests (read / write / native notification) run end-to-end through
+the real ADS stack when the VM is reachable, skip cleanly otherwise.
+**Remaining operational work**: stand up a TwinCAT 3 XAR runtime in a
+Hyper-V VM, author the `.tsproj` project documented at
+`TwinCatProject/README.md`, rotate the 7-day trial license (or buy a
+paid runtime). Unit tests via `FakeTwinCATClient` still carry the
+exhaustive contract coverage.
+
+TwinCAT is the only driver outside Galaxy that uses **native
+notifications** (no polling) for `ISubscribable`, and the fake exposes a
+fire-event harness so notification routing is contract-tested rigorously
+at the unit layer.
+
+## What the fixture is
+
+**Integration layer** (task #221, scaffolded):
+`tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests/` —
+`TwinCATXarFixture` TCP-probes ADS port 48898 on the host specified by
+`TWINCAT_TARGET_HOST` + requires `TWINCAT_TARGET_NETID` (AmsNetId of the
+VM). No fixture-owned lifecycle — XAR can't run in Docker because it
+bypasses the Windows kernel scheduler, so the VM stays
+operator-managed. `TwinCatProject/README.md` documents the required
+`.tsproj` project state; the file itself lands once the XAR VM is up +
+the project is authored. Three smoke tests:
+`Driver_reads_seeded_DINT_through_real_ADS`,
+`Driver_write_then_read_round_trip_on_scratch_REAL`, and
+`Driver_subscribe_receives_native_ADS_notifications_on_counter_changes`
+— all skip cleanly via `[TwinCATFact]` when the runtime isn't
+reachable.
+
+**Unit layer**: `tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/` is
+still the primary coverage. `FakeTwinCATClient` also fakes the
+`AddDeviceNotification` flow so tests can trigger callbacks without a
+running runtime.
+
+## What it actually covers
+
+### Integration (XAR VM, task #221 — code scaffolded, needs VM + project)
+
+- `TwinCAT3SmokeTests.Driver_reads_seeded_DINT_through_real_ADS` — real AMS
+  handshake + ADS read of `GVL_Fixture.nCounter` (seeded at 1234, MAIN
+  increments each cycle)
+- `TwinCAT3SmokeTests.Driver_write_then_read_round_trip_on_scratch_REAL` —
+  real ADS write + read on `GVL_Fixture.rSetpoint`
+- `TwinCAT3SmokeTests.Driver_subscribe_receives_native_ADS_notifications_on_counter_changes`
+  — real `AddDeviceNotification` against the cycle-incrementing counter;
+  observes `OnDataChange` firing within 3 s of subscribe
+
+All three gated on `TWINCAT_TARGET_HOST` + `TWINCAT_TARGET_NETID` env
+vars; skip cleanly via `[TwinCATFact]` when the VM isn't reachable or
+vars are unset.
+
+### Unit
+
+- `TwinCATAmsAddressTests` — `ads://<netId>:<port>` parsing + routing
+- `TwinCATCapabilityTests` — data-type mapping (primitives + declared UDTs),
+  read-only classification
+- `TwinCATReadWriteTests` — read + write through the fake, status mapping
+- `TwinCATSymbolPathTests` — symbol-path routing for nested struct members
+- `TwinCATSymbolBrowserTests` — `ITagDiscovery.DiscoverAsync` via
+  `ReadSymbolsAsync` (#188) + system-symbol filtering
+- `TwinCATNativeNotificationTests` — `AddDeviceNotification` (#189)
+  registration, callback-delivery-to-`OnDataChange` wiring, unregister on
+  unsubscribe
+- `TwinCATDriverTests` — `IDriver` lifecycle
+
+Capability surfaces whose contract is verified: `IDriver`, `IReadable`,
+`IWritable`, `ITagDiscovery`, `ISubscribable`, `IHostConnectivityProbe`,
+`IPerCallHostResolver`.
+
+## What it does NOT cover
+
+### 1. AMS / ADS wire traffic
+
+No real AMS router frame is exchanged. Beckhoff's `TwinCAT.Ads` NuGet (their
+own .NET SDK, not libplctag-style OSS) has no in-process fake; tests stub
+the `ITwinCATClient` abstraction above it.
+
+### 2. Multi-route AMS
+
+ADS supports chained routes (`<localNetId> → <routerNetId> → <targetNetId>`)
+for PLCs behind an EC master / IPC gateway. Parse coverage exists; wire-path
+coverage doesn't.
+
+### 3. Notification reliability under jitter
+
+`AddDeviceNotification` delivers at the runtime's cycle boundary; under high
+CPU load or network jitter real notifications can coalesce. The fake fires
+one callback per test invocation — real callback-coalescing behavior is
+untested.
+
+### 4. TC2 vs TC3 variant handling
+
+TwinCAT 2 (ADS v1) and TwinCAT 3 (ADS v2) have subtly different
+`GetSymbolInfoByName` semantics + symbol-table layouts. Driver targets TC3;
+TC2 compatibility is not exercised.
+
+### 5. Cycle-time alignment for `ISubscribable`
+
+Native ADS notifications fire on the PLC cycle boundary. The fake test
+harness assumes notifications fire on a timer the test controls;
+cycle-aligned firing under real PLC control is not verified.
+
+### 6. Alarms / history
+
+Driver doesn't implement `IAlarmSource` or `IHistoryProvider` — not in
+scope for this driver family. TwinCAT 3's TcEventLogger could theoretically
+back an `IAlarmSource`, but shipping that is a separate feature.
+
+## When to trust TwinCAT tests, when to reach for a rig
+
+| Question | Unit tests | Real TwinCAT runtime |
+| --- | --- | --- |
+| "Does the AMS address parser accept X?" | yes | - |
+| "Does notification → `OnDataChange` wire correctly?" | yes (contract) | yes |
+| "Does symbol browsing filter TwinCAT internals?" | yes | yes |
+| "Does a real ADS read return correct bytes?" | no | yes (required) |
+| "Do notifications coalesce under load?" | no | yes (required) |
+| "Does a TC2 PLC work the same as TC3?" | no | yes (required) |
+
+## Follow-up candidates
+
+1. **XAR VM live-population** — scaffolding is in place (this PR); the
+   remaining work is operational: stand up the Hyper-V VM, install XAR,
+   author the `.tsproj` per `TwinCatProject/README.md`, configure the
+   bilateral ADS route, set `TWINCAT_TARGET_HOST` + `TWINCAT_TARGET_NETID`
+   on the dev box. Then the three smoke tests transition skip → pass.
+   Tracked as #221.
+2. **License-rotation automation** — XAR's 7-day trial expires on
+   schedule. Either automate `TcActivate.exe /reactivate` via a
+   scheduled task on the VM (not officially supported; reportedly works
+   for some TC3 builds), or buy a paid runtime license (~$1k one-time
+   per runtime per CPU) to kill the rotation. The doc at
+   `TwinCatProject/README.md` §License rotation walks through both.
+3. **Lab rig** — cheapest IPC (CX7000 / CX9020) on a dedicated network;
+   the only route that covers TC2 + real EtherCAT I/O timing + cycle
+   jitter under CPU load.
+
+## Key fixture / config files
+
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests/TwinCATXarFixture.cs`
+  — TCP probe + skip-attributes + env-var parsing
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests/TwinCAT3SmokeTests.cs`
+  — three wire-level smoke tests
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests/TwinCatProject/README.md`
+  — project spec + VM setup + license-rotation notes
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/FakeTwinCATClient.cs` —
+  in-process fake with the notification-fire harness used by
+  `TwinCATNativeNotificationTests`
+- `src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATDriver.cs` — ctor takes
+  `ITwinCATClientFactory`

docs/v2/dev-environment.md

@@ -143,15 +143,49 @@ Dev credentials in this inventory are convenience defaults, not secrets. Change
 
 | Resource | Purpose | Type | Default port | Default credentials | Owner |
 |----------|---------|------|--------------|---------------------|-------|
-| **Docker Desktop for Windows** | Host for containerized simulators | Install | (Hyper-V required; not compatible with TwinCAT runtime — see TwinCAT row below for the workaround) | n/a | Integration host admin |
-| **`oitc/modbus-server`** | Modbus TCP simulator (per `test-data-sources.md` §1) | Docker container | 502 (Modbus TCP) | n/a (no auth in protocol) | Integration host admin |
-| **`ab_server`** (libplctag binary) | AB CIP + AB Legacy simulator (per `test-data-sources.md` §2 + §3) | Native binary built from libplctag source; runs in a separate VM or host since it conflicts with Docker Desktop's Hyper-V if run on bare metal | 44818 (CIP) | n/a | Integration host admin |
-| **Snap7 Server** | S7 simulator (per `test-data-sources.md` §4) | Native binary; runs in a separate VM or in WSL2 to avoid Hyper-V conflict | 102 (ISO-TCP) | n/a | Integration host admin |
+| **Docker Desktop for Windows** | Host for every driver test-fixture simulator (Modbus / AB CIP / S7 / OpcUaClient) + SQL Server | Install | (Hyper-V required; not compatible with TwinCAT runtime — see TwinCAT row below for the workaround) | n/a | Integration host admin |
+| **Modbus fixture — `otopcua-pymodbus:3.13.0`** | Modbus driver integration tests | Docker image (local build, see `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/`); 4 compose profiles: `standard` / `dl205` / `mitsubishi` / `s7_1500` | 5020 (non-privileged) | n/a (no auth in protocol) | Developer (per machine) |
+| **AB CIP fixture — `otopcua-ab-server:libplctag-release`** | AB CIP driver integration tests | Docker image (multi-stage build of libplctag's `ab_server` from source, pinned to the `release` tag; see `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/`); 4 compose profiles: `controllogix` / `compactlogix` / `micro800` / `guardlogix` | 44818 (CIP / EtherNet/IP) | n/a | Developer (per machine) |
+| **S7 fixture — `otopcua-python-snap7:1.0`** | S7 driver integration tests | Docker image (local build, `python-snap7>=2.0`; see `tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/Docker/`); 1 compose profile: `s7_1500` | 1102 (non-privileged; driver honours `S7DriverOptions.Port`) | n/a | Developer (per machine) |
+| **OPC UA Client fixture — `mcr.microsoft.com/iotedge/opc-plc:2.14.10`** | OpcUaClient driver integration tests | Docker image (Microsoft-maintained, pinned; see `tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests/Docker/`) | 50000 (OPC UA) | Anonymous (`--daa` off); auto-accept certs (`--aa`) | Developer (per machine) |
 | **TwinCAT XAR runtime VM** | TwinCAT ADS testing (per `test-data-sources.md` §5; Beckhoff XAR cannot coexist with Hyper-V on the same OS) | Hyper-V VM with Windows + TwinCAT XAR installed under 7-day renewable trial | 48898 (ADS over TCP) | TwinCAT default route credentials configured per Beckhoff docs | Integration host admin |
-| **OPC Foundation reference server** | OPC UA Client driver test source (per `test-data-sources.md` §"OPC UA Client") | Built from `OPCFoundation/UA-.NETStandard` `ConsoleReferenceServer` project | 62541 (default for the reference server) | Anonymous + Username (`user1` / `password1`) per the reference server's built-in user list | Integration host admin |
+| **Rockwell Studio 5000 Logix Emulate** | AB CIP golden-box tier — closes UDT / ALMD / AOI / GuardLogix-safety / CompactLogix-ConnectionSize gaps the ab_server simulator can't cover. Loads the L5X project documented at `tests/.../AbCip.IntegrationTests/LogixProject/README.md`. Tests gated on `AB_SERVER_PROFILE=emulate` + `AB_SERVER_ENDPOINT=<ip>:44818`; see `docs/drivers/AbServer-Test-Fixture.md` §Logix Emulate golden-box tier | Windows-only install; **Hyper-V conflict** — can't coexist with Docker Desktop's WSL 2 backend on the same OS, same story as TwinCAT XAR. Runs on a dedicated Windows PC reachable on the LAN | 44818 (CIP / EtherNet/IP) | None required at the CIP layer; Studio 5000 project credentials per Rockwell install | Integration host admin (license + install); Developer (per session — open Emulate, load L5X, click Run) |
 | **FOCAS TCP stub** (`Driver.Focas.TestStub`) | FOCAS functional testing (per `test-data-sources.md` §6) | Local .NET 10 console app from this repo | 8193 (FOCAS) | n/a | Developer / integration host (run on demand) |
 | **FOCAS FaultShim** (`Driver.Focas.FaultShim`) | FOCAS native-fault injection (per `test-data-sources.md` §6) | Test-only native DLL named `Fwlib64.dll`, loaded via DLL search path in the test fixture | n/a (in-process) | n/a | Developer / integration host (test-only) |
 
+### Docker fixtures — quick reference
+
+Every driver's integration-test simulator ships as a Docker image (or pulls
+one from MCR). Start the one you need, run `dotnet test`, stop it.
+Container lifecycle is always manual — fixtures TCP-probe at collection
+init + skip cleanly when nothing's running.
+
+| Driver | Fixture image | Compose file | Bring up |
+|---|---|---|---|
+| Modbus | local-build `otopcua-pymodbus:3.13.0` | `tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/docker-compose.yml` | `docker compose -f <compose> --profile <standard\|dl205\|mitsubishi\|s7_1500> up -d` |
+| AB CIP | local-build `otopcua-ab-server:libplctag-release` | `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/docker-compose.yml` | `docker compose -f <compose> --profile <controllogix\|compactlogix\|micro800\|guardlogix> up -d` |
+| S7 | local-build `otopcua-python-snap7:1.0` | `tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/Docker/docker-compose.yml` | `docker compose -f <compose> --profile s7_1500 up -d` |
+| OpcUaClient | `mcr.microsoft.com/iotedge/opc-plc:2.14.10` (pinned) | `tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests/Docker/docker-compose.yml` | `docker compose -f <compose> up -d` |
+
+First build of a local-build image takes 1–5 minutes; subsequent runs use
+layer cache. `ab_server` is the slowest (multi-stage build clones
+libplctag + compiles C). Stop with `docker compose -f <compose> --profile <…> down`.
+
+**Endpoint overrides** — every fixture respects an env var to point at a
+real PLC instead of the simulator:
+
+- `MODBUS_SIM_ENDPOINT` (default `localhost:5020`)
+- `AB_SERVER_ENDPOINT` (no default; overrides the local container endpoint)
+- `S7_SIM_ENDPOINT` (default `localhost:1102`)
+- `OPCUA_SIM_ENDPOINT` (default `opc.tcp://localhost:50000`)
+
+No native launchers — Docker is the only supported path for these
+fixtures. A fresh clone needs Docker Desktop and nothing else; fixture
+TCP probes skip tests cleanly when the container isn't running.
+
+See each driver's `docs/drivers/*-Test-Fixture.md` for the full coverage
+map + gap inventory.
+
 ### D. Cloud / external services
 
 | Resource | Purpose | Type | Access | Owner |

docs/v2/focas-version-matrix.md

@@ -0,0 +1,145 @@
+# FOCAS version / capability matrix
+
+Authoritative source for the per-CNC-series ranges that
+[`FocasCapabilityMatrix`](../../src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCapabilityMatrix.cs)
+enforces at driver init time. Every row cites the Fanuc FOCAS Developer
+Kit function whose documented input range determines the ceiling.
+
+**Why this exists** — we have no FOCAS hardware on the bench and no
+working simulator. Fwlib32 returns `EW_NUMBER` / `EW_PARAM` when you
+hand it an address outside the controller's supported range; the
+driver would map that to a per-read `BadOutOfRange` at steady state.
+Catching at `InitializeAsync` with this matrix surfaces operator
+typos + mismatched series declarations as config errors before any
+session is opened, which is the only feedback loop available without
+a live CNC to read against.
+
+**Who declares the series** — `FocasDeviceOptions.Series` in
+`appsettings.json`. Defaults to `Unknown`, which is permissive — every
+address passes validation. Pre-matrix configs don't break on upgrade.
+
+---
+
+## Series covered
+
+| Enum value | Controller family | Typical era |
+| --- | --- | --- |
+| `Unknown` | (legacy / not declared) | permissive fallback |
+| `Sixteen_i` | 16i / 18i / 21i | 1997-2008 |
+| `Zero_i_D` | 0i-D | 2008-2013 |
+| `Zero_i_F` | 0i-F | 2013-present, general-purpose |
+| `Zero_i_MF` | 0i-MF | 0i-F lathe variant |
+| `Zero_i_TF` | 0i-TF | 0i-F turning variant |
+| `Thirty_i` | 30i-A / 30i-B | 2007-present, high-end |
+| `ThirtyOne_i` | 31i-A / 31i-B | 30i simpler variant |
+| `ThirtyTwo_i` | 32i-A / 32i-B | 30i compact |
+| `PowerMotion_i` | Power Motion i-A / i-MODEL A | motion-only controller |
+
+## Macro variable range (`cnc_rdmacro` / `cnc_wrmacro`)
+
+Common macros `1-33` + `100-199` + `500-999` are universal across all
+series. Extended macros (`#10000+`) exist only on higher-end series.
+The numbers below reflect the extended ceiling per series per the
+DevKit range tables.
+
+| Series | Min | Max | Notes |
+| --- | ---: | ---: | --- |
+| `Sixteen_i` | 0 | 999 | legacy ceiling — no extended |
+| `Zero_i_D` | 0 | 999 | 0i-D still at legacy ceiling |
+| `Zero_i_F` / `Zero_i_MF` / `Zero_i_TF` | 0 | 9999 | extended added on 0i-F |
+| `Thirty_i` / `ThirtyOne_i` / `ThirtyTwo_i` | 0 | 99999 | full extended set |
+| `PowerMotion_i` | 0 | 999 | atypical — limited macro coverage |
+
+## Parameter range (`cnc_rdparam` / `cnc_wrparam`)
+
+| Series | Min | Max |
+| --- | ---: | ---: |
+| `Sixteen_i` | 0 | 9999 |
+| `Zero_i_D` / `Zero_i_F` / `Zero_i_MF` / `Zero_i_TF` | 0 | 14999 |
+| `Thirty_i` / `ThirtyOne_i` / `ThirtyTwo_i` | 0 | 29999 |
+| `PowerMotion_i` | 0 | 29999 |
+
+## PMC letters (`pmc_rdpmcrng` / `pmc_wrpmcrng`)
+
+Addresses are letter + number (e.g. `R100`, `F50.3`). Legacy
+controllers omit the `F`/`G` signal groups that 30i-family ladder
+programs use, and only the 30i-family exposes `K` (keep-relay) +
+`T` (timer).
+
+| Letter | 16i | 0i-D | 0i-F family | 30i family | Power Motion-i |
+| --- | :-: | :-: | :-: | :-: | :-: |
+| `X` | yes | yes | yes | yes | yes |
+| `Y` | yes | yes | yes | yes | yes |
+| `R` | yes | yes | yes | yes | yes |
+| `D` | yes | yes | yes | yes | yes |
+| `E` | — | yes | yes | yes | — |
+| `A` | — | yes | yes | yes | — |
+| `F` | — | — | yes | yes | — |
+| `G` | — | — | yes | yes | — |
+| `M` | — | — | yes | yes | — |
+| `C` | — | — | yes | yes | — |
+| `K` | — | — | — | yes | — |
+| `T` | — | — | — | yes | — |
+
+Letter match is case-insensitive. `FocasAddress.PmcLetter` is carried
+as a string (not char) so the matrix can do ordinal-ignore-case
+comparison.
+
+## PMC address-number ceiling
+
+PMC addresses are byte-addressed on read + bit-addressed on write;
+`FocasAddress` carries the bit index separately, so these are byte
+ceilings.
+
+| Series | Max byte | Notes |
+| --- | ---: | --- |
+| `Sixteen_i` | 999 | legacy |
+| `Zero_i_D` | 1999 | doubled since 16i |
+| `Zero_i_F` family | 9999 | |
+| `Thirty_i` family | 59999 | highest density |
+| `PowerMotion_i` | 1999 | |
+
+## Error surface
+
+When a tag fails validation, `FocasDriver.InitializeAsync` throws
+`InvalidOperationException` with a message of the form:
+
+```
+FOCAS tag '<name>' (<address>) rejected by capability matrix: <reason>
+```
+
+`<reason>` is the verbatim string from `FocasCapabilityMatrix.Validate`
+and always names the series + the documented limit so the operator
+can either raise the limit (if wrong) or correct the CNC series they
+declared (if mismatched). Sample:
+
+```
+FOCAS tag 'X_axis_macro_ext' (MACRO:50000) rejected by capability
+matrix: Macro variable #50000 is outside the documented range
+[0, 9999] for Zero_i_F.
+```
+
+## How this matrix stays honest
+
+- Every row is covered by a parameterized test in
+  [`FocasCapabilityMatrixTests.cs`](../../tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasCapabilityMatrixTests.cs)
+  — 46 cases across macro / parameter / PMC-letter / PMC-number
+  boundaries + unknown-series permissiveness + rejection-message
+  content + case-insensitivity.
+- Widening or narrowing a range in the matrix without updating this
+  doc will fail a test, because the theories cite the specific row
+  they reflect in their `InlineData`.
+- The matrix is not comprehensive — it encodes only the subset of
+  FOCAS surface the driver currently exposes (Macro / Parameter /
+  PMC). When the driver gains a new capability (e.g. tool management,
+  alarm history), add its series-specific range tables here + matching
+  tests at the same time.
+
+## Follow-up
+
+This validation closes the cheap half of the FOCAS hardware-free
+stability gap — config errors now fail at load instead of per-read.
+The expensive half is Tier-C process isolation so that a crashing
+`Fwlib32.dll` doesn't take the main OPC UA server down with it. See
+[`docs/v2/implementation/focas-isolation-plan.md`](implementation/focas-isolation-plan.md)
+for that plan (task #220).

docs/v2/implementation/adr-001-equipment-node-walker.md

@@ -0,0 +1,248 @@
+# ADR-001 — Equipment node walker: how driver tags bind to the UNS address space
+
+**Status:** Accepted 2026-04-20 — Option A (Config-primary); Option D deferred to v2.1
+
+**Related tasks:** [#195 IdentificationFolderBuilder wire-in](../../../) (blocked on this)
+
+**Related decisions in `plan.md`:** #110 (Tag belongs to Equipment via FK in Equipment ns),
+#116 / #117 / #121 (five identifiers as properties, `Equipment.Name` as path segment),
+#120 (UNS hierarchy mandatory in Equipment ns; SystemPlatform ns exempt).
+
+## Context
+
+Today the `DriverNodeManager` builds its address space by calling
+`ITagDiscovery.DiscoverAsync` on each registered driver. Every driver returns whatever
+browse shape its wire protocol produces — Galaxy returns gobjects with attributes, Modbus
+returns whatever tag configs the operator authored, AB CIP returns controller-walk output,
+etc. The result is a per-driver subtree, rooted under the driver's own namespace, with no
+UNS levels.
+
+The Config DB meanwhile carries the authoritative UNS model for every Equipment-kind
+namespace:
+
+```
+ConfigGeneration
+ └─ ServerCluster
+    └─ Namespace (Kind=Equipment)
+       └─ UnsArea
+          └─ UnsLine
+             └─ Equipment (carries 9 OPC 40010 Identification fields + 5 identifiers)
+                └─ Tag (EquipmentId FK when Kind=Equipment; DriverInstanceId + FolderPath when Kind=SystemPlatform)
+```
+
+Decision #110 already binds `Tag → Equipment` by foreign key. Decision #120 requires the
+Equipment-namespace browse tree to conform to `Enterprise/Site/Area/Line/Equipment/TagName`.
+The building blocks exist:
+
+- `IdentificationFolderBuilder.Build(equipmentBuilder, row)` — pure function that hangs
+  nine OPC 40010 properties under an Equipment node. Shipped, untested in integration.
+- `Equipment` table rows with `UnsLineId` FK + the 9 identification columns + the 5
+  identifier columns.
+- `Tag` table rows with nullable `EquipmentId` + a `TagConfig` JSON column carrying the
+  wire-level address.
+- `NodeScopeResolver` — Phase-1 stub that returns a cluster-level scope only, with an
+  explicit "future resolver will join against the Configuration DB" note.
+
+What's missing is the **walker**: server-side code that reads the UNS + Equipment + Tag
+rows for the current published generation, traverses them in UNS order, materializes each
+level as an OPC UA folder, and wires `IdentificationFolderBuilder.Build` + the 5-identifier
+properties under each Equipment node.
+
+The walker isn't pure bookkeeping — it has to decide **how driver-discovered tags bind to
+UNS Equipment nodes**. That's the decision this ADR resolves.
+
+## Open question
+
+> For an Equipment-kind driver, is the published OPC UA surface driven by (a) the Config
+> DB's `Tag` rows, (b) the driver's `ITagDiscovery.DiscoverAsync` output, or (c) some
+> combination?
+
+SystemPlatform-kind drivers (Galaxy only, today) are unambiguous: decision #120 exempts
+them from UNS + they keep their v1 native hierarchy. The walker does not touch
+SystemPlatform namespaces beyond the existing driver-discovery path. This ADR only decides
+Equipment-kind composition.
+
+## Options
+
+### Option A — Config-primary
+
+The `Tag` table is the sole source of truth for what gets published. `ITagDiscovery`
+becomes a validation + enrichment surface, not a discovery surface.
+
+**Walker flow:**
+
+1. Read `UnsArea` / `UnsLine` / `Equipment` / `Tag` for the published generation.
+2. Walk Area → Line → Equipment, materializing each level as an OPC UA folder.
+3. Under each Equipment node:
+   - Add the 5 identifier properties (`EquipmentId`, `EquipmentUuid`, `MachineCode`,
+     `ZTag`, `SAPID`) as OPC UA properties per decision #121.
+   - Call `IdentificationFolderBuilder.Build` to add the `Identification` sub-folder with
+     the 9 OPC 40010 fields.
+   - For each `Tag` row bound to this Equipment: ask the driver's `IReadable` /
+     `IWritable` surface whether it can address `Tag.TagConfig.address`; if yes, create a
+     variable node. If no, create a `BadNotFound` placeholder with a diagnostic so
+     operators see the mismatch instead of a silent drop.
+4. `ITagDiscovery.DiscoverAsync` is re-purposed to **enrich** — driver may return schema
+   hints (data type, bounds, description) that operators missed when authoring the Tag
+   row. The Admin UI surfaces them as "driver suggests" hints for next-draft edits.
+
+**Trade-offs:**
+
+- ✅ Matches decision #110's framing cleanly. `Tag` rows carry the contract; nothing gets
+  published that's not explicitly authored.
+- ✅ Same model for every Equipment-kind driver. Modbus / S7 / AB CIP / AB Legacy /
+  TwinCAT / FOCAS / OpcUaClient all compose identically.
+- ✅ UNS hierarchy is always exactly as-authored. No race between "driver added a tag at
+  runtime" and "operator hasn't approved it yet."
+- ✅ Aligns with the Config-DB-first operator story the Admin UI already tells.
+- ❌ Drivers with large native schemas (TwinCAT PLCs with thousands of symbols, AB CIP
+  controllers with full @tags walkers) can't "just publish everything" — operators must
+  author Tag rows. This is a pure workflow cost, not a correctness cost.
+- ❌ A Tag row whose driver can't address it produces a placeholder node at runtime
+  (BadNotFound), not a publish-time validation failure. Mitigation: `sp_ValidateDraft`
+  already validates per-driver references at publish — extend it to call each driver's
+  existence check, or keep it as runtime-visible with an Admin UI indicator.
+
+### Option B — Discovery-primary
+
+`ITagDiscovery.DiscoverAsync` is the source of truth for what gets published. The walker
+joins discovered tags against Config-DB Equipment rows to assemble the UNS tree.
+
+**Walker flow:**
+
+1. Driver runs `ITagDiscovery.DiscoverAsync` — returns its native tag graph.
+2. Walker reads `Equipment` + `Tag` rows; uses `Tag.TagConfig.address` to match against
+   discovered references.
+3. For each match: materialize the UNS path + attach the discovered variable under the
+   bound Equipment node.
+4. Discovered tags with no matching `Tag` row: silently dropped (or surfaced under a
+   `Unmapped/` diagnostic folder).
+5. `Tag` rows with no discovered match: hidden (or surfaced as `BadNotFound` placeholder
+   same as Option A).
+
+**Trade-offs:**
+
+- ✅ Lets drivers with rich discovery (TwinCAT `SymbolLoaderFactory`, AB CIP `@tags`)
+  publish live controller state without operator-authored Tag rows for every symbol.
+- ✅ Driver-native metadata (real OPC UA data types, real bounds) is authoritative.
+- ❌ Conflicts with the Config-DB-first publish workflow. Operators publish a generation
+  + discover a different set at runtime + the two don't necessarily match. Diff tooling
+  becomes harder.
+- ❌ Galaxy's SystemPlatform-namespace path still uses Option-B-like discovery — so the
+  codebase would host two compositions regardless. But adding a second
+  discovery-primary composition for Equipment-kind would double the surface operators
+  have to reason about.
+- ❌ Requires each driver to emit tag identifiers that stably match `Tag.TagConfig.address`
+  shape across re-discovery. Works for Galaxy (attribute full refs are stable); harder for
+  AB CIP where the @tags walker may return tags operators haven't declared.
+- ❌ Operator-visible symptom of "my tag didn't publish" splits between two places: the
+  Tag row exists (Config DB) + the driver can't find it (runtime discovery). Option A
+  surfaces the same gap as a single `BadNotFound` placeholder; B multiplies it.
+
+### Option C — Parallel namespaces
+
+Driver tags are always published under a driver-native folder hierarchy (discovery-driven,
+same as today). A secondary UNS "view" namespace is overlaid, containing Equipment nodes
+with Identification sub-folders + `Organizes` references pointing at the driver-native tag
+nodes.
+
+**Walker flow:**
+
+1. Driver's native discovery publishes `ns=2;s={DriverInstanceId}/{...driver shape}` as
+   today.
+2. Walker reads UNS + Equipment + Tag rows.
+3. For each Equipment, creates a node under the UNS namespace (`ns=3;s=UNS/Site/Area/Line/Equipment`)
+   + adds Identification properties + creates `Organizes` references from the Equipment
+   node to the matching driver-native variable nodes.
+
+**Trade-offs:**
+
+- ✅ Preserves the discovery-first driver shape — no change to what Modbus / S7 / AB CIP
+  publish natively; those projects keep working identically.
+- ✅ UNS tree becomes an overlay that operators can opt into or out of. External consumers
+  that want UNS addressing browse via the UNS namespace; consumers that want driver-native
+  addressing keep using the driver namespace.
+- ❌ Doubles the OPC UA node count for every Equipment-kind tag (one node in driver ns,
+  one reference in UNS ns). OPC UA clients handle it but it inflates browse-result sizes.
+- ❌ Contradicts decision #120: "Equipment namespace browse paths must conform to the
+  canonical 5-level Unified Namespace structure." Option C makes the driver namespace
+  browse path NOT conform; the UNS namespace is a second view. An external client that
+  reads the Equipment namespace in driver-native shape doesn't see UNS at all.
+- ❌ Identification ACL semantics get complicated — the sub-folder lives in the UNS ns,
+  but the tag data lives in the driver ns. Two different scope ids; two grants to author.
+
+### Option D — Config-primary with driver-discovery-assist
+
+Same as Option A, but `ITagDiscovery.DiscoverAsync` is called during *draft authoring*
+(not at server runtime) to populate an Admin UI "discovered tags available" panel that
+operators can one-click-add to the draft Tag table. At publish time the Tag rows drive
+the server as in Option A — discovery runs only as an offline helper.
+
+**Trade-offs:**
+
+- ✅ Keeps Option A's runtime semantics — Config DB is the sole publish-time truth.
+- ✅ Closes Option A's only real workflow weakness (authoring Tag rows for large
+  controllers) by letting operators import discovered tags with a click.
+- ✅ Draws a clean line between author-time discovery (optional, offline) and publish-time
+  resolution (strict, Config-DB-driven).
+- ❌ Adds work that isn't on the Phase 6.4 checklist — Admin UI needs a "pull discovered
+  tags from this driver" flow, which means the Admin host needs to proxy a DiscoverAsync
+  call through the Server process (or directly into the driver — more complex deployment
+  topology). v2.1 work, not v2.
+
+## Recommendation
+
+**Pick Option A.** Ship the walker as Config-primary immediately; defer Option D's
+Admin-UI discovery-assist to v2.1 once the walker is proven.
+
+Reasons:
+
+1. **Decision #110 already points here.** `Tag.EquipmentId` + `Tag.TagConfig` are the
+   published contract. Option A is the straight-line implementation of that contract.
+2. **Identical composition across seven drivers.** Every Equipment-kind driver uses the
+   same walker code path. New drivers (e.g. a future OPC UA Client gateway mode) plug in
+   without touching the walker.
+3. **Phase 6.4 Admin UI already authors Tag rows.** CSV import, UnsTab drag/drop, draft
+   diff — all operate on Tag rows. The walker being Tag-row-driven means the Admin UI
+   and the server see the same surface.
+4. **BadNotFound is a clean failure mode.** An operator publishes a Tag row whose
+   address the driver can't reach → client sees a `BadNotFound` variable with a
+   diagnostic, operator fixes the Tag row + republishes. This is legible + easy to
+   debug. Options B and C smear the failure across multiple namespaces.
+5. **Option D is additive, not alternative.** Nothing in A blocks adding D later; the
+   walker contract stays the same, Admin UI just gets a discovery-assist panel.
+
+The walker implementation lands under two tasks this ADR spawns (if accepted):
+
+- **Task A** — Build `EquipmentNodeWalker` in `Core.OpcUa` that drives the
+  `ClusterNode → Namespace → UnsArea → UnsLine → Equipment → Tag` traversal, calls
+  `IdentificationFolderBuilder.Build` per Equipment, materializes the 5 identifier
+  properties, and creates variable nodes for each bound Tag row. Writes integration
+  tests covering the happy path + BadNotFound placeholder.
+- **Task B** — Extend `NodeScopeResolver` to join against Config DB + populate the
+  full `NodeScope` path (UnsAreaId / UnsLineId / EquipmentId / TagId). Unblocks the
+  Phase 6.2 finer-grained ACL (per-Equipment, per-UnsLine grants). Add ACL integration
+  test per task #195 — browse `Equipment/Identification` as unauthorized user,
+  assert `BadUserAccessDenied`.
+
+Task #195 closes on Task B's landing.
+
+## Consequences if we don't decide
+
+- Task #195 stays blocked. The `IdentificationFolderBuilder` exists but is dead code
+  reachable only from its unit tests.
+- `NodeScopeResolver` stays at cluster-level scope. Per-Equipment / per-UnsLine ACL
+  grants work at the Admin UI authoring layer + the data-plane evaluator, but the
+  runtime scope resolution never populates anything below `ClusterId + TagId` — so
+  finer grants are effectively cluster-wide at dispatch. Phase 6.2's rollout plan calls
+  this out as a rollout limitation; it's not a correctness bug but it's a feature gap.
+- Equipment metadata (the 9 OPC 40010 fields, the 5 identifiers) ships in the Config DB
+  + the Admin UI editor but never surfaces on the OPC UA endpoint. External consumers
+  (ERP, SAP PM) can't resolve equipment via OPC UA properties as decision #121 promises.
+
+## Next step
+
+Accept this ADR + spawn Task A + Task B.
+
+If the recommendation is rejected, the alternative options (B / C / D) are ranked by
+implementation cost in the Trade-offs sections above. My strong preference is A + defer D.

docs/v2/implementation/focas-isolation-plan.md

@@ -0,0 +1,163 @@
+# FOCAS Tier-C isolation — plan for task #220
+
+> **Status**: DRAFT — not yet started. Tracks the multi-PR work to
+> move `Fwlib32.dll` behind an out-of-process host, mirroring the
+> Galaxy Tier-C split in [`phase-2-galaxy-out-of-process.md`](phase-2-galaxy-out-of-process.md).
+>
+> **Pre-reqs shipped** (this PR): version matrix + pre-flight
+> validation + unit tests. Those close the cheap half of the
+> hardware-free stability gap. Tier-C closes the expensive half.
+
+## Why isolate
+
+`Fwlib32.dll` is a proprietary Fanuc library with no source, no
+symbols, and a documented habit of crashing the hosting process on
+network errors, malformed responses, and during handle recycling.
+Today the FOCAS driver runs in-process with the OPC UA server —
+a crash inside the Fanuc DLL takes every driver down with it,
+including ones that have nothing to do with FOCAS. Galaxy has the
+same class of problem and solved it with the Tier-C pattern (host
+service + proxy driver + named-pipe IPC); FOCAS should follow that
+playbook.
+
+## Topology (target)
+
+```
++-------------------------------------+         +--------------------------+
+|  OtOpcUa.Server (.NET 10 x64)       |         | OtOpcUaFocasHost         |
+|                                     |  pipe   | (.NET 4.8 x86 Windows    |
+|  ZB.MOM.WW.OtOpcUa.Driver.FOCAS     | <-----> |  service)                |
+|    - FocasProxyDriver (in-proc)     |         |                          |
+|    - supervisor / respawn / BackPr  |         |  Fwlib32.dll + session   |
+|                                     |         |  handles + STA thread    |
++-------------------------------------+         +--------------------------+
+```
+
+Why .NET 4.8 x86 for the host: `Fwlib32.dll` ships as 32-bit only.
+The Galaxy.Host is already .NET 4.8 x86 for the same reason
+(MXAccess COM bitness), so the NSSM wrapper pattern transfers
+directly.
+
+## Three new projects
+
+| Project | TFM | Role |
+| --- | --- | --- |
+| `ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared` | `netstandard2.0` | MessagePack DTOs — `FocasReadRequest`, `FocasReadResponse`, `FocasSubscribeRequest`, `FocasPmcBitWriteRequest`, etc. Same assembly referenced by .NET 10 + .NET 4.8 so the wire format stays identical. |
+| `ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host` | `net48` x86 | Windows service. Owns the Fwlib32 session handles + STA thread + handle-recycling loop. Pipe server + per-call auth (same ACL + caller SID + shared secret pattern as Galaxy.Host). |
+| `ZB.MOM.WW.OtOpcUa.Driver.FOCAS` (existing) | `net10.0` | Collapses to a proxy that forwards each `IReadable` / `IWritable` / `ISubscribable` call over the pipe. `FocasCapabilityMatrix` + `FocasAddress` stay here — pre-flight runs before any IPC. |
+
+## Supervisor responsibilities (in the Proxy)
+
+Mirrors Galaxy.Proxy 1:1:
+
+1. Start the Host process on first `InitializeAsync` (NSSM-wrapped
+   service in production, direct spawn in dev) + heartbeat every
+   5s.
+2. If heartbeat misses 3× in a row, fan out `BadCommunicationError`
+   to every subscription and respawn with exponential backoff
+   (1s / 2s / 4s / max 30s).
+3. Crash-loop circuit breaker: 5 respawns in 60s → drop to
+   `BadDeviceFailure` steady state until operator resets.
+4. Post-mortem MMF: on Host exit, Host writes its last-N operations
+   + session state to an MMF the Proxy reads to log context.
+
+## IPC surface (approximate)
+
+Every `FocasDriver` method that today calls into Fwlib32 directly
+becomes an `ExecuteAsync` call with a typed request:
+
+| Today (in-process) | Tier-C (IPC) |
+| --- | --- |
+| `FocasTagReader.Read(tag)` | `client.Execute(new FocasReadRequest(session, address))` |
+| `FocasTagWriter.Write(tag, value)` | `client.Execute(new FocasWriteRequest(...))` |
+| `FocasPmcBitRmw.Write(tag, bit, value)` | `client.Execute(new FocasPmcBitWriteRequest(...))` — RMW happens in Host so the critical section stays on one process |
+| `FocasConnectivityProbe.ProbeAsync` | `client.Execute(new FocasProbeRequest())` |
+| `FocasSubscriber.Subscribe(tags)` | `client.Execute(new FocasSubscribeRequest(tags))` — Host owns the poll loop + streams changes back as `FocasDataChangedNotification` over the pipe |
+
+Subscription streaming is the non-obvious piece: the Host polls on
+its own timer + pushes change notifications so the Proxy doesn't
+round-trip per poll. Matches `Driver.Galaxy.Host` subscription
+forwarding.
+
+## PR sequence (proposed)
+
+1. **PR A — shared contracts**
+   Create `Driver.FOCAS.Shared` with the MessagePack DTOs. No
+   behaviour change. ~200 LOC + round-trip tests for each DTO.
+2. **PR B — Host project skeleton**
+   Create `Driver.FOCAS.Host` .NET 4.8 x86 project, NSSM wrapper,
+   pipe server scaffold with the same ACL + caller-SID + shared
+   secret plumbing as Galaxy.Host. No Fwlib32 wiring yet — returns
+   `NotImplemented` for everything. ~400 LOC.
+3. **PR C — Move Fwlib32 calls into Host**
+   Move `FocasNativeSession`, `FocasTagReader`, `FocasTagWriter`,
+   `FocasPmcBitRmw` + the STA thread into the Host. Proxy forwards
+   over IPC. This is the biggest PR — probably 800-1500 LOC of
+   move-with-translation. Existing unit tests keep passing because
+   `IFocasTagFactory` is the DI seam the tests inject against.
+4. **PR D — Supervisor + respawn**
+   Proxy-side heartbeat + respawn + crash-loop circuit breaker +
+   BackPressure fan-out on Host death. ~500 LOC + chaos tests.
+5. **PR E — Post-mortem MMF + operational glue**
+   MMF writer in Host, reader in Proxy. Install scripts for the
+   new `OtOpcUaFocasHost` Windows service. Docs. ~300 LOC.
+
+Total estimate: 2200-3200 LOC across 5 PRs. Consistent with Galaxy
+Tier-C but narrower since FOCAS has no Historian + no alarm
+history.
+
+## Testing without hardware
+
+Same constraint as today: no CNC, no simulator. The isolation work
+itself is verifiable without Fwlib32 actually being called:
+
+- **Pipe contract**: PR A's MessagePack round-trip tests cover every
+  DTO.
+- **Supervisor**: PR D uses a `FakeFocasHost` stub that can be told
+  to crash, hang, or miss heartbeats. The supervisor's respawn +
+  circuit-breaker behaviour is fully testable against the stub.
+- **IPC ACL + auth**: reuse the Galaxy.Host's existing test harness
+  pattern — negative tests attempt to connect as the wrong user and
+  assert rejection.
+- **Fwlib32 integration itself**: still untestable without hardware.
+  When a real CNC becomes available, the smoke tests already
+  scaffolded in `tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.IntegrationTests/`
+  run against it via `FOCAS_ENDPOINT`.
+
+## Decisions to confirm before starting
+
+- **Sharing transport code with Galaxy.Host** — should the pipe
+  server + ACL + shared-secret + MMF plumbing go into a common
+  `Core.Hosting.Tier-C` project both hosts reference? Probably yes;
+  deferred until PR B is drafted because the right abstraction only
+  becomes visible after two uses.
+- **Handle-recycling cadence** — Fwlib32 session handles leak
+  memory over weeks per the Fanuc-published defect list. Galaxy
+  recycles MXAccess handles on a 24h timer; FOCAS should mirror but
+  the trigger point (idle vs scheduled) needs operator input.
+- **Per-CNC Host process vs one Host serving N CNCs** — one-per-CNC
+  isolates blast radius but scales poorly past ~20 machines; shared
+  Host scales but one bad CNC can wedge the lot. Start with shared
+  Host + document the blast-radius trade; revisit if operators hit
+  it.
+
+## Non-goals
+
+- Simulator work. `open_focas` + other OSS FOCAS simulators are
+  untested + not maintained; not worth chasing vs. waiting for real
+  hardware.
+- Changing the public `FocasDriverOptions` shape beyond what
+  already shipped (the `Series` knob). Operator config continues to
+  look the same after the split — the Tier-C topology is invisible
+  from `appsettings.json`.
+- Historian / long-term history integration. FOCAS driver doesn't
+  implement `IHistoryProvider` + there's no plan to add it.
+
+## References
+
+- [`docs/v2/implementation/phase-2-galaxy-out-of-process.md`](phase-2-galaxy-out-of-process.md)
+  — the working Tier-C template this plan follows.
+- [`docs/drivers/FOCAS-Test-Fixture.md`](../../drivers/FOCAS-Test-Fixture.md)
+  — what's covered today + what stays blocked on hardware.
+- [`docs/v2/focas-version-matrix.md`](../focas-version-matrix.md) —
+  the capability matrix that pre-flights configs before IPC runs.

docs/v2/modbus-test-plan.md

@@ -13,9 +13,9 @@ confirmed DL205 quirk lands in a follow-up PR as a named test in that project.
 
 ## Harness
 
-**Chosen simulator: pymodbus 3.13.0** (`pip install 'pymodbus[simulator]==3.13.0'`).
-Replaced ModbusPal in PR 43 — see `tests/.../Pymodbus/README.md` for the
-trade-off rationale. Headline reasons:
+**Chosen simulator: pymodbus 3.13.0** packaged as a pinned Docker image
+under `tests/.../Modbus.IntegrationTests/Docker/`. See that folder's
+`README.md` for image-build notes + compose profiles. Headline reasons:
 
 - **Headless** pure-Python CLI; no Java GUI, runs cleanly on a CI runner.
 - **Maintained** — current stable 3.13.0; ModbusPal 1.6b is abandoned.
@@ -26,17 +26,18 @@ trade-off rationale. Headline reasons:
 - **Per-register raw uint16 seeding** — encoding the DL205 string-byte-order
   / BCD / CDAB-float quirks stays explicit (the quirk math lives in the
   `_quirk` JSON-comment fields next to each register).
-- Pip-installable on Windows; sidesteps the privileged-port admin
-  requirement by defaulting to TCP **5020** instead of 502.
+- **Dockerized** — pinned image means the CI simulator surface is
+  reproducible + no `pip install` step on the dev box.
+- Defaults to TCP **5020** (matches the compose port-map + the fixture
+  default endpoint; sidesteps the Windows Firewall prompt on 502).
 
 **Setup pattern**:
-1. `pip install "pymodbus[simulator]==3.13.0"`.
-2. Start the simulator with one of the in-repo profiles:
-   `tests\.../Pymodbus\serve.ps1 -Profile standard` (or `-Profile dl205`).
-3. `dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests` —
+1. `docker compose -f tests\...\Modbus.IntegrationTests\Docker\docker-compose.yml --profile <standard|dl205|mitsubishi|s7_1500> up -d`.
+2. `dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests` —
    tests auto-skip when the endpoint is unreachable. Default endpoint is
    `localhost:5020`; override via `MODBUS_SIM_ENDPOINT` for a real PLC on its
    native port 502.
+3. `docker compose -f ... --profile <…> down` when finished.
 
 ## Per-device quirk catalog
 
@@ -113,9 +114,11 @@ vendors get promoted into driver defaults or opt-in options:
 - **PR 42 — ModbusPal `.xmpp` profiles** — **SUPERSEDED by PR 43**. Replaced
   with pymodbus JSON because ModbusPal 1.6b is abandoned, GUI-only, and only
   exposes 2 of the 4 standard tables.
-- **PR 43 — pymodbus JSON profiles** — **DONE**. `Pymodbus/standard.json` +
-  `Pymodbus/dl205.json` + `Pymodbus/serve.ps1` runner. Both bind TCP 5020.
+- **PR 43 — pymodbus JSON profiles** — **DONE**. Dockerized under
+  `Docker/profiles/` (standard.json, dl205.json, mitsubishi.json,
+  s7_1500.json); compose file launches each via a named profile.
+  All bind TCP 5020.
 - **PR 44+**: one PR per confirmed DL205 quirk, landing the named test + any
   driver-side adjustment (string byte order, BCD decoder, V-memory address
   helper, FC16 cap-per-device-family) needed to pass it. Each quirk's value
-  is already pre-encoded in `Pymodbus/dl205.json`.
+  is already pre-encoded in `Docker/profiles/dl205.json`.

docs/v2/test-data-sources.md

@@ -191,40 +191,30 @@ Modbus has no native String, DateTime, or Int64 — those rows are skipped on th
 
 ### CI fixture (task #180)
 
-The integration harness at `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/` exposes two test-time contracts:
+The integration harness at `tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/` is Docker-only — `ab_server` is a source-only tool under libplctag's `src/tools/ab_server/`, and the fixture's multi-stage `Docker/Dockerfile` is the only supported reproducible build path.
 
-- **`AbServerFixture(AbServerProfile)`** — starts the simulator with the CLI args composed from the profile's `--plc` family + seed-tag set. One fixture instance per family, one simulator process per test case (smoke tier). For larger suites that can share a simulator across several reads/writes, use a `IClassFixture<AbServerFixture>` wrapper per family.
-- **`KnownProfiles.{ControlLogix, CompactLogix, Micro800, GuardLogix}`** — the four per-family profiles. Drives the simulator's `--plc` mode + the preseed `--tag name:type[:size]` set. Micro800 + GuardLogix fall back to `controllogix` under the hood because ab_server has no dedicated mode for them — the driver-side family profile still enforces the narrower connection shape / safety classification separately.
+- **`AbServerFixture(AbServerProfile)`** — thin TCP probe against `127.0.0.1:44818` (or `AB_SERVER_ENDPOINT` override). Does not spawn the simulator; the operator brings up the compose service for whichever family the test class targets (`controllogix` / `compactlogix` / `micro800` / `guardlogix`).
+- **`KnownProfiles.{ControlLogix, CompactLogix, Micro800, GuardLogix}`** — thin `(Family, ComposeProfile, Notes)` records. The compose file (`Docker/docker-compose.yml`) is the canonical source of truth for which tags each family seeds + which `--plc` mode the simulator boots in. `Micro800` uses the dedicated `--plc=Micro800` mode; `GuardLogix` uses `ControlLogix` emulation because ab_server has no safety subsystem (the `_S`-suffixed seed tag triggers driver-side ViewOnly classification only).
 
-**Pinned version** (recorded in `ci/ab-server.lock.json` so drift is one-file visible):
-
-- `libplctag` **v2.6.16** (published 2026-03-29) — `ab_server.exe` ships inside the `_tools.zip` asset alongside `plctag.dll` + two `list_tags_*` helpers.
-- Windows x64: `libplctag_2.6.16_windows_x64_tools.zip` — SHA256 `9b78a3dee73d9cd28ca348c090f453dbe3ad9d07ad6bf42865a9dc3a79bc2232`
-- Windows x86: `libplctag_2.6.16_windows_x86_tools.zip` — SHA256 `fdfefd58b266c5da9a1ded1a430985e609289c9e67be2544da7513b668761edf`
-- Windows ARM64: `libplctag_2.6.16_windows_arm64_tools.zip` — SHA256 `d747728e4c4958bb63b4ac23e1c820c4452e4778dfd7d58f8a0aecd5402d4944`
+**Pinned version**: the `Docker/Dockerfile` clones libplctag at a pinned tag (currently the `release` branch) via its `LIBPLCTAG_TAG` build-arg and compiles `ab_server` from source. Bump deliberately alongside a driver-side change that needs the newer simulator.
 
 **CI step:**
 
 ```yaml
 # GitHub Actions step placed before `dotnet test`:
-- name: Fetch ab_server (libplctag v2.6.16)
+- name: Start ab_server Docker container
   shell: pwsh
   run: |
-    $pin = Get-Content ci/ab-server.lock.json | ConvertFrom-Json
-    $asset = $pin.assets.'windows-x64'       # swap to windows-x86 / windows-arm64 on non-x64 runners
-    $url = "https://github.com/libplctag/libplctag/releases/download/$($pin.tag)/$($asset.file)"
-    $zip = Join-Path $env:RUNNER_TEMP 'libplctag-tools.zip'
-    Invoke-WebRequest $url -OutFile $zip
-    $actual = (Get-FileHash -Algorithm SHA256 $zip).Hash.ToLower()
-    if ($actual -ne $asset.sha256) { throw "libplctag tools SHA256 mismatch: expected $($asset.sha256), got $actual" }
-    $dest = Join-Path $env:RUNNER_TEMP 'libplctag-tools'
-    Expand-Archive $zip -DestinationPath $dest
-    Add-Content $env:GITHUB_PATH $dest
+    docker compose -f tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/docker-compose.yml `
+      --profile controllogix up -d --build
+    # Wait for :44818 to accept connections (compose healthcheck-equivalent)
+    for ($i = 0; $i -lt 30; $i++) {
+      if ((Test-NetConnection -ComputerName localhost -Port 44818 -WarningAction SilentlyContinue).TcpTestSucceeded) { break }
+      Start-Sleep -Seconds 1
+    }
 ```
 
-The fixture's `LocateBinary()` picks the binary up off PATH so the C# harness doesn't own the download — CI YAML is the right place for version pinning + hash verification. Developer workstations install the binary once from source (`cmake + make ab_server` under a libplctag clone) and the same fixture works identically.
-
-Tests without ab_server on PATH are marked `Skip` via `AbServerFactAttribute` / `AbServerTheoryAttribute`, so fresh-clone runs without the simulator still pass all unit suites in this project.
+Tests skip via `AbServerFactAttribute` / `AbServerTheoryAttribute` when the probe fails, so fresh-clone runs without Docker still pass all unit suites in this project.
 
 ---
 

src/ZB.MOM.WW.OtOpcUa.Core/OpcUa/EquipmentNodeWalker.cs

@@ -0,0 +1,173 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+/// <summary>
+///     Materializes the canonical Unified Namespace browse tree for an Equipment-kind
+///     <see cref="Configuration.Entities.Namespace"/> from the Config DB's
+///     <c>UnsArea</c> / <c>UnsLine</c> / <c>Equipment</c> / <c>Tag</c> rows. Runs during
+///     address-space build per <see cref="IDriver"/> whose
+///     <c>Namespace.Kind = Equipment</c>; SystemPlatform-kind namespaces (Galaxy) are
+///     exempt per decision #120 and reach this walker only indirectly through
+///     <see cref="ITagDiscovery.DiscoverAsync"/>.
+/// </summary>
+/// <remarks>
+///     <para>
+///         <b>Composition strategy.</b> ADR-001 (2026-04-20) accepted Option A — Config
+///         primary. The walker treats the supplied <see cref="EquipmentNamespaceContent"/>
+///         snapshot as the authoritative published surface. Every Equipment row becomes a
+///         folder node at the UNS level-5 segment; every <see cref="Tag"/> bound to an
+///         Equipment (non-null <see cref="Tag.EquipmentId"/>) becomes a variable node under
+///         it. Driver-discovered tags that have no Config-DB row are not added by this
+///         walker — the ITagDiscovery path continues to exist for the SystemPlatform case +
+///         for enrichment, but Equipment-kind composition is fully Tag-row-driven.
+///     </para>
+///
+///     <para>
+///         <b>Under each Equipment node.</b> Five identifier properties per decision #121
+///         (<c>EquipmentId</c>, <c>EquipmentUuid</c>, <c>MachineCode</c>, <c>ZTag</c>,
+///         <c>SAPID</c>) are added as OPC UA properties — external systems (ERP, SAP PM)
+///         resolve equipment by whichever identifier they natively use without a sidecar.
+///         <see cref="IdentificationFolderBuilder.Build"/> materializes the OPC 40010
+///         Identification sub-folder with the nine decision-#139 fields when at least one
+///         is non-null; when all nine are null the sub-folder is omitted rather than
+///         appearing empty.
+///     </para>
+///
+///     <para>
+///         <b>Address resolution.</b> Variable nodes carry the driver-side full reference
+///         in <see cref="DriverAttributeInfo.FullName"/> copied from <c>Tag.TagConfig</c>
+///         (the wire-level address JSON blob whose interpretation is driver-specific). At
+///         runtime the dispatch layer routes Read/Write calls through the configured
+///         capability invoker; an unreachable address surfaces as an OPC UA Bad status via
+///         the natural driver-read failure path, NOT as a build-time reject. The ADR calls
+///         this "BadNotFound placeholder" behavior — legible to operators via their Admin
+///         UI + OPC UA client inspection of node status.
+///     </para>
+///
+///     <para>
+///         <b>Pure function.</b> This class has no dependency on the OPC UA SDK, no
+///         Config-DB access, no state. It consumes pre-loaded EF Core rows + streams calls
+///         into the supplied <see cref="IAddressSpaceBuilder"/>. The server-side wiring
+///         (load snapshot → invoke walker → per-tag capability probe) lives in the Task B
+///         PR alongside <c>NodeScopeResolver</c>'s Config-DB join.
+///     </para>
+/// </remarks>
+public static class EquipmentNodeWalker
+{
+    /// <summary>
+    ///     Walk <paramref name="content"/> into <paramref name="namespaceBuilder"/>.
+    ///     The builder is scoped to the Equipment-kind namespace root; the walker emits
+    ///     Area → Line → Equipment folders under it, then identifier properties + the
+    ///     Identification sub-folder + variable nodes per bound Tag under each Equipment.
+    /// </summary>
+    /// <param name="namespaceBuilder">
+    ///     The builder scoped to the Equipment-kind namespace root. Caller is responsible for
+    ///     creating this (e.g. <c>rootBuilder.Folder(namespace.NamespaceId, namespace.NamespaceUri)</c>).
+    /// </param>
+    /// <param name="content">Pre-loaded + pre-filtered rows for a single published generation.</param>
+    public static void Walk(IAddressSpaceBuilder namespaceBuilder, EquipmentNamespaceContent content)
+    {
+        ArgumentNullException.ThrowIfNull(namespaceBuilder);
+        ArgumentNullException.ThrowIfNull(content);
+
+        // Group lines by area + equipment by line + tags by equipment up-front. Avoids an
+        // O(N·M) re-scan at each UNS level on large fleets.
+        var linesByArea = content.Lines
+            .GroupBy(l => l.UnsAreaId, StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(g => g.Key, g => g.OrderBy(l => l.Name, StringComparer.Ordinal).ToList(), StringComparer.OrdinalIgnoreCase);
+
+        var equipmentByLine = content.Equipment
+            .GroupBy(e => e.UnsLineId, StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(g => g.Key, g => g.OrderBy(e => e.Name, StringComparer.Ordinal).ToList(), StringComparer.OrdinalIgnoreCase);
+
+        var tagsByEquipment = content.Tags
+            .Where(t => !string.IsNullOrEmpty(t.EquipmentId))
+            .GroupBy(t => t.EquipmentId!, StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(g => g.Key, g => g.OrderBy(t => t.Name, StringComparer.Ordinal).ToList(), StringComparer.OrdinalIgnoreCase);
+
+        foreach (var area in content.Areas.OrderBy(a => a.Name, StringComparer.Ordinal))
+        {
+            var areaBuilder = namespaceBuilder.Folder(area.Name, area.Name);
+            if (!linesByArea.TryGetValue(area.UnsAreaId, out var areaLines)) continue;
+
+            foreach (var line in areaLines)
+            {
+                var lineBuilder = areaBuilder.Folder(line.Name, line.Name);
+                if (!equipmentByLine.TryGetValue(line.UnsLineId, out var lineEquipment)) continue;
+
+                foreach (var equipment in lineEquipment)
+                {
+                    var equipmentBuilder = lineBuilder.Folder(equipment.Name, equipment.Name);
+                    AddIdentifierProperties(equipmentBuilder, equipment);
+                    IdentificationFolderBuilder.Build(equipmentBuilder, equipment);
+
+                    if (!tagsByEquipment.TryGetValue(equipment.EquipmentId, out var equipmentTags)) continue;
+                    foreach (var tag in equipmentTags)
+                        AddTagVariable(equipmentBuilder, tag);
+                }
+            }
+        }
+    }
+
+    /// <summary>
+    ///     Adds the five operator-facing identifiers from decision #121 as OPC UA properties
+    ///     on the Equipment node. EquipmentId + EquipmentUuid are always populated;
+    ///     MachineCode is required per <see cref="Equipment"/>; ZTag + SAPID are nullable in
+    ///     the data model so they're skipped when null to avoid empty-string noise in the
+    ///     browse tree.
+    /// </summary>
+    private static void AddIdentifierProperties(IAddressSpaceBuilder equipmentBuilder, Equipment equipment)
+    {
+        equipmentBuilder.AddProperty("EquipmentId", DriverDataType.String, equipment.EquipmentId);
+        equipmentBuilder.AddProperty("EquipmentUuid", DriverDataType.String, equipment.EquipmentUuid.ToString());
+        equipmentBuilder.AddProperty("MachineCode", DriverDataType.String, equipment.MachineCode);
+        if (!string.IsNullOrEmpty(equipment.ZTag))
+            equipmentBuilder.AddProperty("ZTag", DriverDataType.String, equipment.ZTag);
+        if (!string.IsNullOrEmpty(equipment.SAPID))
+            equipmentBuilder.AddProperty("SAPID", DriverDataType.String, equipment.SAPID);
+    }
+
+    /// <summary>
+    ///     Emit a single Tag row as an <see cref="IAddressSpaceBuilder.Variable"/>. The driver
+    ///     full reference lives in <c>Tag.TagConfig</c> (wire-level address, driver-specific
+    ///     JSON blob); the variable node's data type derives from <c>Tag.DataType</c>.
+    ///     Unreachable-address behavior per ADR-001 Option A: the variable is created; the
+    ///     driver's natural Read failure surfaces an OPC UA Bad status at runtime.
+    /// </summary>
+    private static void AddTagVariable(IAddressSpaceBuilder equipmentBuilder, Tag tag)
+    {
+        var attr = new DriverAttributeInfo(
+            FullName: tag.TagConfig,
+            DriverDataType: ParseDriverDataType(tag.DataType),
+            IsArray: false,
+            ArrayDim: null,
+            SecurityClass: SecurityClassification.FreeAccess,
+            IsHistorized: false);
+        equipmentBuilder.Variable(tag.Name, tag.Name, attr);
+    }
+
+    /// <summary>
+    ///     Parse <see cref="Tag.DataType"/> (stored as the <see cref="DriverDataType"/> enum
+    ///     name string, decision #138) into the enum value. Unknown names fall back to
+    ///     <see cref="DriverDataType.String"/> so a one-off driver-specific type doesn't
+    ///     abort the whole walk; the underlying driver still sees the original TagConfig
+    ///     address + can surface its own typed value via the OPC UA variant at read time.
+    /// </summary>
+    private static DriverDataType ParseDriverDataType(string raw) =>
+        Enum.TryParse<DriverDataType>(raw, ignoreCase: true, out var parsed) ? parsed : DriverDataType.String;
+}
+
+/// <summary>
+///     Pre-loaded + pre-filtered snapshot of one Equipment-kind namespace's worth of Config
+///     DB rows. All four collections are scoped to the same
+///     <see cref="Configuration.Entities.ConfigGeneration"/> + the same
+///     <see cref="Configuration.Entities.Namespace"/> row. The walker assumes this filter
+///     was applied by the caller + does no cross-generation or cross-namespace validation.
+/// </summary>
+public sealed record EquipmentNamespaceContent(
+    IReadOnlyList<UnsArea> Areas,
+    IReadOnlyList<UnsLine> Lines,
+    IReadOnlyList<Equipment> Equipment,
+    IReadOnlyList<Tag> Tags);

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipAlarmProjection.cs

@@ -0,0 +1,232 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+/// <summary>
+///     Task #177 — projects AB Logix ALMD alarm instructions onto the OPC UA alarm surface by
+///     polling the ALMD UDT's <c>InFaulted</c> / <c>Acked</c> / <c>Severity</c> members at a
+///     configurable interval + translating state transitions into <c>OnAlarmEvent</c>
+///     callbacks on the owning <see cref="AbCipDriver"/>. Feature-flagged off by default via
+///     <see cref="AbCipDriverOptions.EnableAlarmProjection"/>; callers that leave the flag off
+///     get a no-op subscribe path so capability negotiation still works.
+/// </summary>
+/// <remarks>
+///     <para>ALMD-only in this pass. ALMA (analog alarm) projection is a follow-up because
+///     its threshold + limit semantics need more design — ALMD's "is the alarm active + has
+///     the operator acked" shape maps cleanly onto the driver-agnostic
+///     <see cref="IAlarmSource"/> contract without concessions.</para>
+///
+///     <para>Polling reuses <see cref="AbCipDriver.ReadAsync"/>, so ALMD reads get the #194
+///     whole-UDT optimization for free when the ALMD is declared with its standard members.
+///     One poll loop per subscription call; the loop batches every
+///     member read across the full source-node set into a single ReadAsync per tick.</para>
+///
+///     <para>ALMD <c>Acked</c> write semantics on Logix are rising-edge sensitive at the
+///     instruction level — writing <c>Acked=1</c> directly is honored by FT View + the
+///     standard HMI templates, but some PLC programs read <c>AckCmd</c> + look for the edge
+///     themselves. We pick the simpler <c>Acked</c> write for first pass; operators whose
+///     ladder watches <c>AckCmd</c> can wire a follow-up "AckCmd 0→1→0" pulse on the client
+///     side until a driver-level knob lands.</para>
+/// </remarks>
+internal sealed class AbCipAlarmProjection : IAsyncDisposable
+{
+    private readonly AbCipDriver _driver;
+    private readonly TimeSpan _pollInterval;
+    private readonly Dictionary<long, Subscription> _subs = new();
+    private readonly Lock _subsLock = new();
+    private long _nextId;
+
+    public AbCipAlarmProjection(AbCipDriver driver, TimeSpan pollInterval)
+    {
+        _driver = driver;
+        _pollInterval = pollInterval;
+    }
+
+    public async Task<IAlarmSubscriptionHandle> SubscribeAsync(
+        IReadOnlyList<string> sourceNodeIds, CancellationToken cancellationToken)
+    {
+        var id = Interlocked.Increment(ref _nextId);
+        var handle = new AbCipAlarmSubscriptionHandle(id);
+        var cts = new CancellationTokenSource();
+        var sub = new Subscription(handle, [..sourceNodeIds], cts);
+
+        lock (_subsLock) _subs[id] = sub;
+
+        sub.Loop = Task.Run(() => RunPollLoopAsync(sub, cts.Token), cts.Token);
+        await Task.CompletedTask;
+        return handle;
+    }
+
+    public async Task UnsubscribeAsync(IAlarmSubscriptionHandle handle, CancellationToken cancellationToken)
+    {
+        if (handle is not AbCipAlarmSubscriptionHandle h) return;
+        Subscription? sub;
+        lock (_subsLock)
+        {
+            if (!_subs.Remove(h.Id, out sub)) return;
+        }
+        try { sub.Cts.Cancel(); } catch { }
+        try { await sub.Loop.ConfigureAwait(false); } catch { }
+        sub.Cts.Dispose();
+    }
+
+    public async Task AcknowledgeAsync(
+        IReadOnlyList<AlarmAcknowledgeRequest> acknowledgements, CancellationToken cancellationToken)
+    {
+        if (acknowledgements.Count == 0) return;
+
+        // Write Acked=1 per request. IWritable isn't on AbCipAlarmProjection so route through
+        // the driver's public interface — delegating instead of re-implementing the write path
+        // keeps the bit-in-DINT + idempotency + per-call-host-resolve knobs intact.
+        var requests = acknowledgements
+            .Select(a => new WriteRequest($"{a.SourceNodeId}.Acked", true))
+            .ToArray();
+        // Best-effort — the driver's WriteAsync returns per-item status; individual ack
+        // failures don't poison the batch. Swallow the return so a single faulted ack
+        // doesn't bubble out of the caller's batch expectation.
+        _ = await _driver.WriteAsync(requests, cancellationToken).ConfigureAwait(false);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        List<Subscription> snap;
+        lock (_subsLock) { snap = _subs.Values.ToList(); _subs.Clear(); }
+        foreach (var sub in snap)
+        {
+            try { sub.Cts.Cancel(); } catch { }
+            try { await sub.Loop.ConfigureAwait(false); } catch { }
+            sub.Cts.Dispose();
+        }
+    }
+
+    /// <summary>
+    ///     Poll-tick body — reads <c>InFaulted</c> + <c>Severity</c> for every source node id
+    ///     in the subscription, diffs each against last-seen state, fires raise/clear events.
+    ///     Extracted so tests can drive one tick without standing up the Task.Run loop.
+    /// </summary>
+    internal void Tick(Subscription sub, IReadOnlyList<DataValueSnapshot> results)
+    {
+        // results index layout: for each sourceNode, [InFaulted, Severity] in order.
+        for (var i = 0; i < sub.SourceNodeIds.Count; i++)
+        {
+            var nodeId = sub.SourceNodeIds[i];
+            var inFaultedDv = results[i * 2];
+            var severityDv = results[i * 2 + 1];
+            if (inFaultedDv.StatusCode != AbCipStatusMapper.Good) continue;
+
+            var nowFaulted = ToBool(inFaultedDv.Value);
+            var severity = ToInt(severityDv.Value);
+
+            var wasFaulted = sub.LastInFaulted.GetValueOrDefault(nodeId, false);
+            sub.LastInFaulted[nodeId] = nowFaulted;
+
+            if (!wasFaulted && nowFaulted)
+            {
+                _driver.InvokeAlarmEvent(new AlarmEventArgs(
+                    sub.Handle, nodeId, ConditionId: $"{nodeId}#active",
+                    AlarmType: "ALMD",
+                    Message: $"ALMD {nodeId} raised",
+                    Severity: MapSeverity(severity),
+                    SourceTimestampUtc: DateTime.UtcNow));
+            }
+            else if (wasFaulted && !nowFaulted)
+            {
+                _driver.InvokeAlarmEvent(new AlarmEventArgs(
+                    sub.Handle, nodeId, ConditionId: $"{nodeId}#active",
+                    AlarmType: "ALMD",
+                    Message: $"ALMD {nodeId} cleared",
+                    Severity: MapSeverity(severity),
+                    SourceTimestampUtc: DateTime.UtcNow));
+            }
+        }
+    }
+
+    private async Task RunPollLoopAsync(Subscription sub, CancellationToken ct)
+    {
+        var refs = new List<string>(sub.SourceNodeIds.Count * 2);
+        foreach (var nodeId in sub.SourceNodeIds)
+        {
+            refs.Add($"{nodeId}.InFaulted");
+            refs.Add($"{nodeId}.Severity");
+        }
+
+        while (!ct.IsCancellationRequested)
+        {
+            try
+            {
+                var results = await _driver.ReadAsync(refs, ct).ConfigureAwait(false);
+                Tick(sub, results);
+            }
+            catch (OperationCanceledException) when (ct.IsCancellationRequested) { break; }
+            catch { /* per-tick failures are non-fatal; next tick retries */ }
+
+            try { await Task.Delay(_pollInterval, ct).ConfigureAwait(false); }
+            catch (OperationCanceledException) { break; }
+        }
+    }
+
+    internal static AlarmSeverity MapSeverity(int raw) => raw switch
+    {
+        <= 250 => AlarmSeverity.Low,
+        <= 500 => AlarmSeverity.Medium,
+        <= 750 => AlarmSeverity.High,
+        _ => AlarmSeverity.Critical,
+    };
+
+    private static bool ToBool(object? v) => v switch
+    {
+        bool b => b,
+        int i => i != 0,
+        long l => l != 0,
+        _ => false,
+    };
+
+    private static int ToInt(object? v) => v switch
+    {
+        int i => i,
+        long l => (int)l,
+        short s => s,
+        byte b => b,
+        _ => 0,
+    };
+
+    internal sealed class Subscription
+    {
+        public Subscription(AbCipAlarmSubscriptionHandle handle, IReadOnlyList<string> sourceNodeIds, CancellationTokenSource cts)
+        {
+            Handle = handle; SourceNodeIds = sourceNodeIds; Cts = cts;
+        }
+        public AbCipAlarmSubscriptionHandle Handle { get; }
+        public IReadOnlyList<string> SourceNodeIds { get; }
+        public CancellationTokenSource Cts { get; }
+        public Task Loop { get; set; } = Task.CompletedTask;
+        public Dictionary<string, bool> LastInFaulted { get; } = new(StringComparer.Ordinal);
+    }
+}
+
+/// <summary>Handle returned by <see cref="AbCipAlarmProjection.SubscribeAsync"/>.</summary>
+public sealed record AbCipAlarmSubscriptionHandle(long Id) : IAlarmSubscriptionHandle
+{
+    public string DiagnosticId => $"abcip-alarm-sub-{Id}";
+}
+
+/// <summary>
+///     Detects the ALMD / ALMA signature in an <see cref="AbCipTagDefinition"/>'s declared
+///     members. Used by both discovery (to stamp <c>IsAlarm=true</c> on the emitted
+///     variable) + initial driver setup (to decide which tags the alarm projection owns).
+/// </summary>
+public static class AbCipAlarmDetector
+{
+    /// <summary>
+    ///     <c>true</c> when <paramref name="tag"/> is a Structure whose declared members match
+    ///     the ALMD signature (<c>InFaulted</c> + <c>Acked</c> present). ALMA detection
+    ///     (analog alarms with <c>HHLimit</c>/<c>HLimit</c>/<c>LLimit</c>/<c>LLLimit</c>)
+    ///     ships as a follow-up.
+    /// </summary>
+    public static bool IsAlmd(AbCipTagDefinition tag)
+    {
+        if (tag.DataType != AbCipDataType.Structure || tag.Members is null) return false;
+        var names = tag.Members.Select(m => m.Name).ToHashSet(StringComparer.OrdinalIgnoreCase);
+        return names.Contains("InFaulted") && names.Contains("Acked");
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriver.cs

@@ -21,7 +21,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
 ///     <see cref="PlcTagHandle"/> and reconnects each device.</para>
 /// </remarks>
 public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery, ISubscribable,
-    IHostConnectivityProbe, IPerCallHostResolver, IDisposable, IAsyncDisposable
+    IHostConnectivityProbe, IPerCallHostResolver, IAlarmSource, IDisposable, IAsyncDisposable
 {
     private readonly AbCipDriverOptions _options;
     private readonly string _driverInstanceId;
@@ -32,10 +32,15 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     private readonly PollGroupEngine _poll;
     private readonly Dictionary<string, DeviceState> _devices = new(StringComparer.OrdinalIgnoreCase);
     private readonly Dictionary<string, AbCipTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
+    private readonly AbCipAlarmProjection _alarmProjection;
     private DriverHealth _health = new(DriverState.Unknown, null, null);
 
     public event EventHandler<DataChangeEventArgs>? OnDataChange;
     public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;
+    public event EventHandler<AlarmEventArgs>? OnAlarmEvent;
+
+    /// <summary>Internal seam for the alarm projection to raise events through the driver.</summary>
+    internal void InvokeAlarmEvent(AlarmEventArgs args) => OnAlarmEvent?.Invoke(this, args);
 
     public AbCipDriver(AbCipDriverOptions options, string driverInstanceId,
         IAbCipTagFactory? tagFactory = null,
@@ -52,6 +57,7 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             reader: ReadAsync,
             onChange: (handle, tagRef, snapshot) =>
                 OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)));
+        _alarmProjection = new AbCipAlarmProjection(this, _options.AlarmPollInterval);
     }
 
     /// <summary>
@@ -162,6 +168,7 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
     public async Task ShutdownAsync(CancellationToken cancellationToken)
     {
+        await _alarmProjection.DisposeAsync().ConfigureAwait(false);
         await _poll.DisposeAsync().ConfigureAwait(false);
         foreach (var state in _devices.Values)
         {
@@ -187,6 +194,39 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         return Task.CompletedTask;
     }
 
+    // ---- IAlarmSource (ALMD projection, #177) ----
+
+    /// <summary>
+    ///     Subscribe to ALMD alarm transitions on <paramref name="sourceNodeIds"/>. Each id
+    ///     names a declared ALMD UDT tag; the projection polls the tag's <c>InFaulted</c> +
+    ///     <c>Severity</c> members at <see cref="AbCipDriverOptions.AlarmPollInterval"/> and
+    ///     fires <see cref="OnAlarmEvent"/> on 0→1 (raise) + 1→0 (clear) transitions.
+    ///     Feature-gated — when <see cref="AbCipDriverOptions.EnableAlarmProjection"/> is
+    ///     <c>false</c> (the default), returns a handle wrapping a no-op subscription so
+    ///     capability negotiation still works; <see cref="OnAlarmEvent"/> never fires.
+    /// </summary>
+    public Task<IAlarmSubscriptionHandle> SubscribeAlarmsAsync(
+        IReadOnlyList<string> sourceNodeIds, CancellationToken cancellationToken)
+    {
+        if (!_options.EnableAlarmProjection)
+        {
+            var disabled = new AbCipAlarmSubscriptionHandle(0);
+            return Task.FromResult<IAlarmSubscriptionHandle>(disabled);
+        }
+        return _alarmProjection.SubscribeAsync(sourceNodeIds, cancellationToken);
+    }
+
+    public Task UnsubscribeAlarmsAsync(IAlarmSubscriptionHandle handle, CancellationToken cancellationToken) =>
+        _options.EnableAlarmProjection
+            ? _alarmProjection.UnsubscribeAsync(handle, cancellationToken)
+            : Task.CompletedTask;
+
+    public Task AcknowledgeAsync(
+        IReadOnlyList<AlarmAcknowledgeRequest> acknowledgements, CancellationToken cancellationToken) =>
+        _options.EnableAlarmProjection
+            ? _alarmProjection.AcknowledgeAsync(acknowledgements, cancellationToken)
+            : Task.CompletedTask;
+
     // ---- IHostConnectivityProbe ----
 
     public IReadOnlyList<HostConnectivityStatus> GetHostStatuses() =>
@@ -287,56 +327,127 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         var now = DateTime.UtcNow;
         var results = new DataValueSnapshot[fullReferences.Count];
 
-        for (var i = 0; i < fullReferences.Count; i++)
-        {
-            var reference = fullReferences[i];
-            if (!_tagsByName.TryGetValue(reference, out var def))
-            {
-                results[i] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
-                continue;
-            }
-            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
-            {
-                results[i] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
-                continue;
-            }
+        // Task #194 — plan the batch: members of the same parent UDT get collapsed into one
+        // whole-UDT read + in-memory member decode; every other reference falls back to the
+        // per-tag path that's been here since PR 3. Planner is a pure function over the
+        // current tag map; BOOL/String/Structure members stay on the fallback path because
+        // declaration-only offsets can't place them under Logix alignment rules.
+        var plan = AbCipUdtReadPlanner.Build(fullReferences, _tagsByName);
 
-            try
-            {
-                var runtime = await EnsureTagRuntimeAsync(device, def, cancellationToken).ConfigureAwait(false);
-                await runtime.ReadAsync(cancellationToken).ConfigureAwait(false);
+        foreach (var group in plan.Groups)
+            await ReadGroupAsync(group, results, now, cancellationToken).ConfigureAwait(false);
 
-                var status = runtime.GetStatus();
-                if (status != 0)
-                {
-                    results[i] = new DataValueSnapshot(null,
-                        AbCipStatusMapper.MapLibplctagStatus(status), null, now);
-                    _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
-                        $"libplctag status {status} reading {reference}");
-                    continue;
-                }
-
-                var tagPath = AbCipTagPath.TryParse(def.TagPath);
-                var bitIndex = tagPath?.BitIndex;
-                var value = runtime.DecodeValue(def.DataType, bitIndex);
-                results[i] = new DataValueSnapshot(value, AbCipStatusMapper.Good, now, now);
-                _health = new DriverHealth(DriverState.Healthy, now, null);
-            }
-            catch (OperationCanceledException)
-            {
-                throw;
-            }
-            catch (Exception ex)
-            {
-                results[i] = new DataValueSnapshot(null,
-                    AbCipStatusMapper.BadCommunicationError, null, now);
-                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
-            }
-        }
+        foreach (var fb in plan.Fallbacks)
+            await ReadSingleAsync(fb, fullReferences[fb.OriginalIndex], results, now, cancellationToken).ConfigureAwait(false);
 
         return results;
     }
 
+    private async Task ReadSingleAsync(
+        AbCipUdtReadFallback fb, string reference, DataValueSnapshot[] results, DateTime now, CancellationToken ct)
+    {
+        if (!_tagsByName.TryGetValue(reference, out var def))
+        {
+            results[fb.OriginalIndex] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
+            return;
+        }
+        if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
+        {
+            results[fb.OriginalIndex] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
+            return;
+        }
+
+        try
+        {
+            var runtime = await EnsureTagRuntimeAsync(device, def, ct).ConfigureAwait(false);
+            await runtime.ReadAsync(ct).ConfigureAwait(false);
+
+            var status = runtime.GetStatus();
+            if (status != 0)
+            {
+                results[fb.OriginalIndex] = new DataValueSnapshot(null,
+                    AbCipStatusMapper.MapLibplctagStatus(status), null, now);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
+                    $"libplctag status {status} reading {reference}");
+                return;
+            }
+
+            var tagPath = AbCipTagPath.TryParse(def.TagPath);
+            var bitIndex = tagPath?.BitIndex;
+            var value = runtime.DecodeValue(def.DataType, bitIndex);
+            results[fb.OriginalIndex] = new DataValueSnapshot(value, AbCipStatusMapper.Good, now, now);
+            _health = new DriverHealth(DriverState.Healthy, now, null);
+        }
+        catch (OperationCanceledException)
+        {
+            throw;
+        }
+        catch (Exception ex)
+        {
+            results[fb.OriginalIndex] = new DataValueSnapshot(null,
+                AbCipStatusMapper.BadCommunicationError, null, now);
+            _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+        }
+    }
+
+    /// <summary>
+    ///     Task #194 — perform one whole-UDT read on the parent tag, then decode each
+    ///     grouped member from the runtime's buffer at its computed byte offset. A per-group
+    ///     failure (parent read raised, non-zero libplctag status, or missing device) stamps
+    ///     the mapped fault across every grouped member only — sibling groups + the
+    ///     per-tag fallback list are unaffected.
+    /// </summary>
+    private async Task ReadGroupAsync(
+        AbCipUdtReadGroup group, DataValueSnapshot[] results, DateTime now, CancellationToken ct)
+    {
+        var parent = group.ParentDefinition;
+
+        if (!_devices.TryGetValue(parent.DeviceHostAddress, out var device))
+        {
+            StampGroupStatus(group, results, now, AbCipStatusMapper.BadNodeIdUnknown);
+            return;
+        }
+
+        try
+        {
+            var runtime = await EnsureTagRuntimeAsync(device, parent, ct).ConfigureAwait(false);
+            await runtime.ReadAsync(ct).ConfigureAwait(false);
+
+            var status = runtime.GetStatus();
+            if (status != 0)
+            {
+                var mapped = AbCipStatusMapper.MapLibplctagStatus(status);
+                StampGroupStatus(group, results, now, mapped);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
+                    $"libplctag status {status} reading UDT {group.ParentName}");
+                return;
+            }
+
+            foreach (var member in group.Members)
+            {
+                var value = runtime.DecodeValueAt(member.Definition.DataType, member.Offset, bitIndex: null);
+                results[member.OriginalIndex] = new DataValueSnapshot(value, AbCipStatusMapper.Good, now, now);
+            }
+            _health = new DriverHealth(DriverState.Healthy, now, null);
+        }
+        catch (OperationCanceledException)
+        {
+            throw;
+        }
+        catch (Exception ex)
+        {
+            StampGroupStatus(group, results, now, AbCipStatusMapper.BadCommunicationError);
+            _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+        }
+    }
+
+    private static void StampGroupStatus(
+        AbCipUdtReadGroup group, DataValueSnapshot[] results, DateTime now, uint statusCode)
+    {
+        foreach (var member in group.Members)
+            results[member.OriginalIndex] = new DataValueSnapshot(null, statusCode, null, now);
+    }
+
     // ---- IWritable ----
 
     /// <summary>

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriverOptions.cs

@@ -38,6 +38,24 @@ public sealed class AbCipDriverOptions
     ///     should appear in the address space.
     /// </summary>
     public bool EnableControllerBrowse { get; init; }
+
+    /// <summary>
+    ///     Task #177 — when <c>true</c>, declared ALMD tags are surfaced as alarm conditions
+    ///     via <see cref="Core.Abstractions.IAlarmSource"/>; the driver polls each subscribed
+    ///     alarm's <c>InFaulted</c> + <c>Severity</c> members + fires <c>OnAlarmEvent</c> on
+    ///     state transitions. Default <c>false</c> — operators explicitly opt in because
+    ///     projection semantics don't exactly mirror Rockwell FT Alarm &amp; Events; shops
+    ///     running FT Live should keep this off + take alarms through the native route.
+    /// </summary>
+    public bool EnableAlarmProjection { get; init; }
+
+    /// <summary>
+    ///     Poll interval for the ALMD projection loop. Shorter intervals catch faster edges
+    ///     at the cost of PLC round-trips; edges shorter than this interval are invisible to
+    ///     the projection (a 0→1→0 transition within one tick collapses to no event). Default
+    ///     1 second — matches typical SCADA alarm-refresh conventions.
+    /// </summary>
+    public TimeSpan AlarmPollInterval { get; init; } = TimeSpan.FromSeconds(1);
 }
 
 /// <summary>

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipUdtMemberLayout.cs

@@ -0,0 +1,78 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+/// <summary>
+///     Computes byte offsets for declared UDT members under Logix natural-alignment rules so
+///     a single whole-UDT read (task #194) can decode each member from one buffer without
+///     re-reading per member. Declaration-driven — the caller supplies
+///     <see cref="AbCipStructureMember"/> rows; this helper produces the offset each member
+///     sits at in the parent tag's read buffer.
+/// </summary>
+/// <remarks>
+///     <para>Alignment rules applied per Rockwell "Logix 5000 Data Access" manual + the
+///     libplctag test fixtures: each member aligns to its natural boundary (SInt 1, Int 2,
+///     DInt/Real/Dt 4, LInt/ULInt/LReal 8), padding inserted before the member as needed.
+///     The total size is padded to the alignment of the largest member so arrays-of-UDT also
+///     work at element stride — though this helper is used only on single instances today.</para>
+///
+///     <para><see cref="TryBuild"/> returns <c>null</c> on unsupported member types
+///     (<see cref="AbCipDataType.Bool"/>, <see cref="AbCipDataType.String"/>,
+///     <see cref="AbCipDataType.Structure"/>). Whole-UDT grouping opts out of those groups
+///     and falls back to the per-tag read path — BOOL members are packed into a hidden host
+///     byte at the top of the UDT under Logix, so their offset can't be computed from
+///     declared-member order alone. The CIP Template Object reader produces a
+///     <see cref="AbCipUdtShape"/> that carries real offsets for BOOL + nested structs; when
+///     that shape is cached the driver can take the richer path instead.</para>
+/// </remarks>
+public static class AbCipUdtMemberLayout
+{
+    /// <summary>
+    ///     Try to compute member offsets for the supplied declared members. Returns <c>null</c>
+    ///     if any member type is unsupported for declaration-only layout.
+    /// </summary>
+    public static IReadOnlyDictionary<string, int>? TryBuild(
+        IReadOnlyList<AbCipStructureMember> members)
+    {
+        ArgumentNullException.ThrowIfNull(members);
+        if (members.Count == 0) return null;
+
+        var offsets = new Dictionary<string, int>(members.Count, StringComparer.OrdinalIgnoreCase);
+        var cursor = 0;
+
+        foreach (var member in members)
+        {
+            if (!TryGetSizeAlign(member.DataType, out var size, out var align))
+                return null;
+
+            if (cursor % align != 0)
+                cursor += align - (cursor % align);
+
+            offsets[member.Name] = cursor;
+            cursor += size;
+        }
+
+        return offsets;
+    }
+
+    /// <summary>
+    ///     Natural size + alignment for a Logix atomic type. <c>false</c> for types excluded
+    ///     from declaration-only grouping (Bool / String / Structure).
+    /// </summary>
+    private static bool TryGetSizeAlign(AbCipDataType type, out int size, out int align)
+    {
+        switch (type)
+        {
+            case AbCipDataType.SInt: case AbCipDataType.USInt:
+                size = 1; align = 1; return true;
+            case AbCipDataType.Int: case AbCipDataType.UInt:
+                size = 2; align = 2; return true;
+            case AbCipDataType.DInt: case AbCipDataType.UDInt:
+            case AbCipDataType.Real: case AbCipDataType.Dt:
+                size = 4; align = 4; return true;
+            case AbCipDataType.LInt: case AbCipDataType.ULInt:
+            case AbCipDataType.LReal:
+                size = 8; align = 8; return true;
+            default:
+                size = 0; align = 0; return false;
+        }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipUdtReadPlanner.cs

@@ -0,0 +1,109 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+/// <summary>
+///     Task #194 — groups a ReadAsync batch of full-references into whole-UDT reads where
+///     possible. A group is emitted for every parent UDT tag whose declared
+///     <see cref="AbCipStructureMember"/>s produced a valid offset map AND at least two of
+///     its members appear in the batch; every other reference stays in the per-tag fallback
+///     list that <see cref="AbCipDriver.ReadAsync"/> runs through its existing read path.
+///     Pure function — the planner never touches the runtime + never reads the PLC.
+/// </summary>
+public static class AbCipUdtReadPlanner
+{
+    /// <summary>
+    ///     Split <paramref name="requests"/> into whole-UDT groups + per-tag leftovers.
+    ///     <paramref name="tagsByName"/> is the driver's <c>_tagsByName</c> map — both parent
+    ///     UDT rows and their fanned-out member rows live there. Lookup is OrdinalIgnoreCase
+    ///     to match the driver's dictionary semantics.
+    /// </summary>
+    public static AbCipUdtReadPlan Build(
+        IReadOnlyList<string> requests,
+        IReadOnlyDictionary<string, AbCipTagDefinition> tagsByName)
+    {
+        ArgumentNullException.ThrowIfNull(requests);
+        ArgumentNullException.ThrowIfNull(tagsByName);
+
+        var fallback = new List<AbCipUdtReadFallback>(requests.Count);
+        var byParent = new Dictionary<string, List<AbCipUdtReadMember>>(StringComparer.OrdinalIgnoreCase);
+
+        for (var i = 0; i < requests.Count; i++)
+        {
+            var name = requests[i];
+            if (!tagsByName.TryGetValue(name, out var def))
+            {
+                fallback.Add(new AbCipUdtReadFallback(i, name));
+                continue;
+            }
+
+            var (parentName, memberName) = SplitParentMember(name);
+            if (parentName is null || memberName is null
+                || !tagsByName.TryGetValue(parentName, out var parent)
+                || parent.DataType != AbCipDataType.Structure
+                || parent.Members is not { Count: > 0 })
+            {
+                fallback.Add(new AbCipUdtReadFallback(i, name));
+                continue;
+            }
+
+            var offsets = AbCipUdtMemberLayout.TryBuild(parent.Members);
+            if (offsets is null || !offsets.TryGetValue(memberName, out var offset))
+            {
+                fallback.Add(new AbCipUdtReadFallback(i, name));
+                continue;
+            }
+
+            if (!byParent.TryGetValue(parentName, out var members))
+            {
+                members = new List<AbCipUdtReadMember>();
+                byParent[parentName] = members;
+            }
+            members.Add(new AbCipUdtReadMember(i, def, offset));
+        }
+
+        // A single-member group saves nothing (one whole-UDT read replaces one per-member read)
+        // — demote to fallback to avoid paying the cost of reading the full UDT buffer only to
+        // pull one field out.
+        var groups = new List<AbCipUdtReadGroup>(byParent.Count);
+        foreach (var (parentName, members) in byParent)
+        {
+            if (members.Count < 2)
+            {
+                foreach (var m in members)
+                    fallback.Add(new AbCipUdtReadFallback(m.OriginalIndex, m.Definition.Name));
+                continue;
+            }
+            groups.Add(new AbCipUdtReadGroup(parentName, tagsByName[parentName], members));
+        }
+
+        return new AbCipUdtReadPlan(groups, fallback);
+    }
+
+    private static (string? Parent, string? Member) SplitParentMember(string reference)
+    {
+        var dot = reference.IndexOf('.');
+        if (dot <= 0 || dot == reference.Length - 1) return (null, null);
+        return (reference[..dot], reference[(dot + 1)..]);
+    }
+}
+
+/// <summary>A planner output: grouped UDT reads + per-tag fallbacks.</summary>
+public sealed record AbCipUdtReadPlan(
+    IReadOnlyList<AbCipUdtReadGroup> Groups,
+    IReadOnlyList<AbCipUdtReadFallback> Fallbacks);
+
+/// <summary>One UDT parent whose members were batched into a single read.</summary>
+public sealed record AbCipUdtReadGroup(
+    string ParentName,
+    AbCipTagDefinition ParentDefinition,
+    IReadOnlyList<AbCipUdtReadMember> Members);
+
+/// <summary>
+///     One member inside an <see cref="AbCipUdtReadGroup"/>. <c>OriginalIndex</c> is the
+///     slot in the caller's request list so the decoded value lands at the correct output
+///     offset. <c>Definition</c> is the fanned-out member-level tag definition. <c>Offset</c>
+///     is the byte offset within the parent UDT buffer where this member lives.
+/// </summary>
+public sealed record AbCipUdtReadMember(int OriginalIndex, AbCipTagDefinition Definition, int Offset);
+
+/// <summary>A reference that falls back to the per-tag read path.</summary>
+public sealed record AbCipUdtReadFallback(int OriginalIndex, string Reference);

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/IAbCipTagRuntime.cs

@@ -31,6 +31,17 @@ public interface IAbCipTagRuntime : IDisposable
     /// </summary>
     object? DecodeValue(AbCipDataType type, int? bitIndex);
 
+    /// <summary>
+    ///     Decode a value at an arbitrary byte offset in the local buffer. Task #194 —
+    ///     whole-UDT reads perform one <see cref="ReadAsync"/> on the parent UDT tag then
+    ///     call this per declared member with its computed offset, avoiding one libplctag
+    ///     round-trip per member. Implementations that do not support offset-aware decoding
+    ///     may fall back to <see cref="DecodeValue"/> when <paramref name="offset"/> is zero;
+    ///     offsets greater than zero against an unsupporting runtime should return <c>null</c>
+    ///     so the planner can skip grouping.
+    /// </summary>
+    object? DecodeValueAt(AbCipDataType type, int offset, int? bitIndex);
+
     /// <summary>
     ///     Encode <paramref name="value"/> into the local buffer per the tag's type. Callers
     ///     pair this with <see cref="WriteAsync"/>.

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/LibplctagTagRuntime.cs

@@ -32,24 +32,26 @@ internal sealed class LibplctagTagRuntime : IAbCipTagRuntime
 
     public int GetStatus() => (int)_tag.GetStatus();
 
-    public object? DecodeValue(AbCipDataType type, int? bitIndex) => type switch
+    public object? DecodeValue(AbCipDataType type, int? bitIndex) => DecodeValueAt(type, 0, bitIndex);
+
+    public object? DecodeValueAt(AbCipDataType type, int offset, int? bitIndex) => type switch
     {
         AbCipDataType.Bool => bitIndex is int bit
             ? _tag.GetBit(bit)
-            : _tag.GetInt8(0) != 0,
-        AbCipDataType.SInt => (int)(sbyte)_tag.GetInt8(0),
-        AbCipDataType.USInt => (int)_tag.GetUInt8(0),
-        AbCipDataType.Int => (int)_tag.GetInt16(0),
-        AbCipDataType.UInt => (int)_tag.GetUInt16(0),
-        AbCipDataType.DInt => _tag.GetInt32(0),
-        AbCipDataType.UDInt => (int)_tag.GetUInt32(0),
-        AbCipDataType.LInt => _tag.GetInt64(0),
-        AbCipDataType.ULInt => (long)_tag.GetUInt64(0),
-        AbCipDataType.Real => _tag.GetFloat32(0),
-        AbCipDataType.LReal => _tag.GetFloat64(0),
-        AbCipDataType.String => _tag.GetString(0),
-        AbCipDataType.Dt => _tag.GetInt32(0), // seconds-since-epoch DINT; consumer widens as needed
-        AbCipDataType.Structure => null,       // UDT whole-tag decode lands in PR 6
+            : _tag.GetInt8(offset) != 0,
+        AbCipDataType.SInt => (int)(sbyte)_tag.GetInt8(offset),
+        AbCipDataType.USInt => (int)_tag.GetUInt8(offset),
+        AbCipDataType.Int => (int)_tag.GetInt16(offset),
+        AbCipDataType.UInt => (int)_tag.GetUInt16(offset),
+        AbCipDataType.DInt => _tag.GetInt32(offset),
+        AbCipDataType.UDInt => (int)_tag.GetUInt32(offset),
+        AbCipDataType.LInt => _tag.GetInt64(offset),
+        AbCipDataType.ULInt => (long)_tag.GetUInt64(offset),
+        AbCipDataType.Real => _tag.GetFloat32(offset),
+        AbCipDataType.LReal => _tag.GetFloat64(offset),
+        AbCipDataType.String => _tag.GetString(offset),
+        AbCipDataType.Dt => _tag.GetInt32(offset),
+        AbCipDataType.Structure => null,
         _ => null,
     };
 

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Backend/FakeFocasBackend.cs

@@ -0,0 +1,122 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Backend;
+
+/// <summary>
+///     In-memory <see cref="IFocasBackend"/> for tests + an operational stub mode when
+///     <c>OTOPCUA_FOCAS_BACKEND=fake</c>. Keeps per-address values keyed by a canonical
+///     string; RMW semantics honor PMC bit-writes against the containing byte so the
+///     <c>PmcBitWriteRequest</c> path can be exercised end-to-end without hardware.
+/// </summary>
+public sealed class FakeFocasBackend : IFocasBackend
+{
+    private readonly object _gate = new();
+    private long _nextSessionId;
+    private readonly HashSet<long> _openSessions = [];
+    private readonly Dictionary<string, byte[]> _pmcValues = [];
+    private readonly Dictionary<string, byte[]> _paramValues = [];
+    private readonly Dictionary<string, byte[]> _macroValues = [];
+
+    public Task<OpenSessionResponse> OpenSessionAsync(OpenSessionRequest request, CancellationToken ct)
+    {
+        lock (_gate)
+        {
+            var id = ++_nextSessionId;
+            _openSessions.Add(id);
+            return Task.FromResult(new OpenSessionResponse { Success = true, SessionId = id });
+        }
+    }
+
+    public Task CloseSessionAsync(CloseSessionRequest request, CancellationToken ct)
+    {
+        lock (_gate) { _openSessions.Remove(request.SessionId); }
+        return Task.CompletedTask;
+    }
+
+    public Task<ReadResponse> ReadAsync(ReadRequest request, CancellationToken ct)
+    {
+        lock (_gate)
+        {
+            if (!_openSessions.Contains(request.SessionId))
+                return Task.FromResult(new ReadResponse { Success = false, StatusCode = 0x80020000u, Error = "session-not-open" });
+
+            var store = StoreFor(request.Address.Kind);
+            var key = CanonicalKey(request.Address);
+            store.TryGetValue(key, out var value);
+            return Task.FromResult(new ReadResponse
+            {
+                Success = true,
+                StatusCode = 0,
+                ValueBytes = value ?? MessagePackSerializer.Serialize((int)0),
+                ValueTypeCode = request.DataType,
+                SourceTimestampUtcUnixMs = System.DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+            });
+        }
+    }
+
+    public Task<WriteResponse> WriteAsync(WriteRequest request, CancellationToken ct)
+    {
+        lock (_gate)
+        {
+            if (!_openSessions.Contains(request.SessionId))
+                return Task.FromResult(new WriteResponse { Success = false, StatusCode = 0x80020000u, Error = "session-not-open" });
+
+            var store = StoreFor(request.Address.Kind);
+            store[CanonicalKey(request.Address)] = request.ValueBytes ?? [];
+            return Task.FromResult(new WriteResponse { Success = true, StatusCode = 0 });
+        }
+    }
+
+    public Task<PmcBitWriteResponse> PmcBitWriteAsync(PmcBitWriteRequest request, CancellationToken ct)
+    {
+        lock (_gate)
+        {
+            if (!_openSessions.Contains(request.SessionId))
+                return Task.FromResult(new PmcBitWriteResponse { Success = false, StatusCode = 0x80020000u, Error = "session-not-open" });
+            if (request.BitIndex is < 0 or > 7)
+                return Task.FromResult(new PmcBitWriteResponse { Success = false, StatusCode = 0x803C0000u, Error = "bit-out-of-range" });
+
+            var key = CanonicalKey(request.Address);
+            _pmcValues.TryGetValue(key, out var current);
+            current ??= MessagePackSerializer.Serialize((byte)0);
+            var b = MessagePackSerializer.Deserialize<byte>(current);
+            var mask = (byte)(1 << request.BitIndex);
+            b = request.Value ? (byte)(b | mask) : (byte)(b & ~mask);
+            _pmcValues[key] = MessagePackSerializer.Serialize(b);
+            return Task.FromResult(new PmcBitWriteResponse { Success = true, StatusCode = 0 });
+        }
+    }
+
+    public Task<ProbeResponse> ProbeAsync(ProbeRequest request, CancellationToken ct)
+    {
+        lock (_gate)
+        {
+            return Task.FromResult(new ProbeResponse
+            {
+                Healthy = _openSessions.Contains(request.SessionId),
+                ObservedAtUtcUnixMs = System.DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+            });
+        }
+    }
+
+    private Dictionary<string, byte[]> StoreFor(int kind) => kind switch
+    {
+        0 => _pmcValues,
+        1 => _paramValues,
+        2 => _macroValues,
+        _ => _pmcValues,
+    };
+
+    private static string CanonicalKey(FocasAddressDto addr) =>
+        addr.Kind switch
+        {
+            0 => $"{addr.PmcLetter}{addr.Number}",
+            1 => $"P{addr.Number}",
+            2 => $"M{addr.Number}",
+            _ => $"?{addr.Number}",
+        };
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Backend/IFocasBackend.cs

@@ -0,0 +1,24 @@
+using System.Threading;
+using System.Threading.Tasks;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Backend;
+
+/// <summary>
+///     The Host's view of a FOCAS session. One implementation wraps the real
+///     <c>Fwlib32.dll</c> via P/Invoke (lands with the real Fwlib32 integration follow-up,
+///     since no hardware is available today); a second implementation —
+///     <see cref="FakeFocasBackend"/> — is used by tests.
+///     Both live on .NET 4.8 x86 so the Host can be deployed in either mode without
+///     changing the pipe server.
+///     Invoked via <c>FwlibFrameHandler</c> in the Ipc namespace.
+/// </summary>
+public interface IFocasBackend
+{
+    Task<OpenSessionResponse> OpenSessionAsync(OpenSessionRequest request, CancellationToken ct);
+    Task CloseSessionAsync(CloseSessionRequest request, CancellationToken ct);
+    Task<ReadResponse> ReadAsync(ReadRequest request, CancellationToken ct);
+    Task<WriteResponse> WriteAsync(WriteRequest request, CancellationToken ct);
+    Task<PmcBitWriteResponse> PmcBitWriteAsync(PmcBitWriteRequest request, CancellationToken ct);
+    Task<ProbeResponse> ProbeAsync(ProbeRequest request, CancellationToken ct);
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Backend/UnconfiguredFocasBackend.cs

@@ -0,0 +1,37 @@
+using System.Threading;
+using System.Threading.Tasks;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Backend;
+
+/// <summary>
+///     Safe default when the deployment hasn't configured a real Fwlib32 backend.
+///     Returns structured failure responses instead of throwing so the Proxy can map the
+///     error to <c>BadDeviceFailure</c> and surface a clear operator message pointing at
+///     <c>docs/v2/focas-deployment.md</c>. Used when <c>OTOPCUA_FOCAS_BACKEND</c> is unset
+///     or set to <c>unconfigured</c>.
+/// </summary>
+public sealed class UnconfiguredFocasBackend : IFocasBackend
+{
+    private const uint BadDeviceFailure = 0x80550000u;
+    private const string Reason =
+        "FOCAS Host is running without a real Fwlib32 backend. Set OTOPCUA_FOCAS_BACKEND=fwlib32 " +
+        "and ensure Fwlib32.dll is on PATH — see docs/v2/focas-deployment.md.";
+
+    public Task<OpenSessionResponse> OpenSessionAsync(OpenSessionRequest request, CancellationToken ct) =>
+        Task.FromResult(new OpenSessionResponse { Success = false, Error = Reason, ErrorCode = "NoFwlibBackend" });
+
+    public Task CloseSessionAsync(CloseSessionRequest request, CancellationToken ct) => Task.CompletedTask;
+
+    public Task<ReadResponse> ReadAsync(ReadRequest request, CancellationToken ct) =>
+        Task.FromResult(new ReadResponse { Success = false, StatusCode = BadDeviceFailure, Error = Reason });
+
+    public Task<WriteResponse> WriteAsync(WriteRequest request, CancellationToken ct) =>
+        Task.FromResult(new WriteResponse { Success = false, StatusCode = BadDeviceFailure, Error = Reason });
+
+    public Task<PmcBitWriteResponse> PmcBitWriteAsync(PmcBitWriteRequest request, CancellationToken ct) =>
+        Task.FromResult(new PmcBitWriteResponse { Success = false, StatusCode = BadDeviceFailure, Error = Reason });
+
+    public Task<ProbeResponse> ProbeAsync(ProbeRequest request, CancellationToken ct) =>
+        Task.FromResult(new ProbeResponse { Healthy = false, Error = Reason, ObservedAtUtcUnixMs = System.DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() });
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Ipc/FwlibFrameHandler.cs

@@ -0,0 +1,111 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Backend;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+
+/// <summary>
+///     Real FOCAS frame handler. Deserializes each request DTO, delegates to
+///     <see cref="IFocasBackend"/>, re-serializes the response. The backend owns the
+///     Fwlib32 handle + STA thread — the handler is pure dispatch.
+/// </summary>
+public sealed class FwlibFrameHandler : IFrameHandler
+{
+    private readonly IFocasBackend _backend;
+    private readonly ILogger _logger;
+
+    public FwlibFrameHandler(IFocasBackend backend, ILogger logger)
+    {
+        _backend = backend ?? throw new ArgumentNullException(nameof(backend));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    public async Task HandleAsync(FocasMessageKind kind, byte[] body, FrameWriter writer, CancellationToken ct)
+    {
+        try
+        {
+            switch (kind)
+            {
+                case FocasMessageKind.Heartbeat:
+                {
+                    var hb = MessagePackSerializer.Deserialize<Heartbeat>(body);
+                    await writer.WriteAsync(FocasMessageKind.HeartbeatAck,
+                        new HeartbeatAck
+                        {
+                            MonotonicTicks = hb.MonotonicTicks,
+                            HostUtcUnixMs = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+                        }, ct).ConfigureAwait(false);
+                    return;
+                }
+
+                case FocasMessageKind.OpenSessionRequest:
+                {
+                    var req = MessagePackSerializer.Deserialize<OpenSessionRequest>(body);
+                    var resp = await _backend.OpenSessionAsync(req, ct).ConfigureAwait(false);
+                    await writer.WriteAsync(FocasMessageKind.OpenSessionResponse, resp, ct).ConfigureAwait(false);
+                    return;
+                }
+
+                case FocasMessageKind.CloseSessionRequest:
+                {
+                    var req = MessagePackSerializer.Deserialize<CloseSessionRequest>(body);
+                    await _backend.CloseSessionAsync(req, ct).ConfigureAwait(false);
+                    return;
+                }
+
+                case FocasMessageKind.ReadRequest:
+                {
+                    var req = MessagePackSerializer.Deserialize<ReadRequest>(body);
+                    var resp = await _backend.ReadAsync(req, ct).ConfigureAwait(false);
+                    await writer.WriteAsync(FocasMessageKind.ReadResponse, resp, ct).ConfigureAwait(false);
+                    return;
+                }
+
+                case FocasMessageKind.WriteRequest:
+                {
+                    var req = MessagePackSerializer.Deserialize<WriteRequest>(body);
+                    var resp = await _backend.WriteAsync(req, ct).ConfigureAwait(false);
+                    await writer.WriteAsync(FocasMessageKind.WriteResponse, resp, ct).ConfigureAwait(false);
+                    return;
+                }
+
+                case FocasMessageKind.PmcBitWriteRequest:
+                {
+                    var req = MessagePackSerializer.Deserialize<PmcBitWriteRequest>(body);
+                    var resp = await _backend.PmcBitWriteAsync(req, ct).ConfigureAwait(false);
+                    await writer.WriteAsync(FocasMessageKind.PmcBitWriteResponse, resp, ct).ConfigureAwait(false);
+                    return;
+                }
+
+                case FocasMessageKind.ProbeRequest:
+                {
+                    var req = MessagePackSerializer.Deserialize<ProbeRequest>(body);
+                    var resp = await _backend.ProbeAsync(req, ct).ConfigureAwait(false);
+                    await writer.WriteAsync(FocasMessageKind.ProbeResponse, resp, ct).ConfigureAwait(false);
+                    return;
+                }
+
+                default:
+                    await writer.WriteAsync(FocasMessageKind.ErrorResponse,
+                        new ErrorResponse { Code = "unknown-kind", Message = $"Kind {kind} is not handled by the Host" },
+                        ct).ConfigureAwait(false);
+                    return;
+            }
+        }
+        catch (OperationCanceledException) { throw; }
+        catch (Exception ex)
+        {
+            _logger.Error(ex, "FwlibFrameHandler error processing {Kind}", kind);
+            await writer.WriteAsync(FocasMessageKind.ErrorResponse,
+                new ErrorResponse { Code = "backend-exception", Message = ex.Message },
+                ct).ConfigureAwait(false);
+        }
+    }
+
+    public IDisposable AttachConnection(FrameWriter writer) => IFrameHandler.NoopAttachment.Instance;
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Ipc/IFrameHandler.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+
+/// <summary>
+///     Dispatches a single IPC frame to the backend. Implementations own the FOCAS session
+///     state and translate request DTOs into Fwlib32 calls.
+/// </summary>
+public interface IFrameHandler
+{
+    Task HandleAsync(FocasMessageKind kind, byte[] body, FrameWriter writer, CancellationToken ct);
+
+    /// <summary>
+    ///     Called once per accepted connection after the Hello handshake. Lets the handler
+    ///     attach server-pushed event sinks (data-change notifications, runtime-status
+    ///     changes) to the connection's <paramref name="writer"/>. Returns an
+    ///     <see cref="IDisposable"/> the pipe server disposes when the connection closes —
+    ///     backends use it to unsubscribe from their push sources.
+    /// </summary>
+    IDisposable AttachConnection(FrameWriter writer);
+
+    public sealed class NoopAttachment : IDisposable
+    {
+        public static readonly NoopAttachment Instance = new();
+        public void Dispose() { }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Ipc/PipeAcl.cs

@@ -0,0 +1,39 @@
+using System;
+using System.IO.Pipes;
+using System.Security.AccessControl;
+using System.Security.Principal;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+
+/// <summary>
+///     Builds the <see cref="PipeSecurity"/> for the FOCAS Host pipe. Same pattern as
+///     Galaxy.Host: only the configured OtOpcUa server principal SID gets
+///     <c>ReadWrite | Synchronize</c>; LocalSystem + Administrators are explicitly denied
+///     so a compromised service account on the same host can't escalate via the pipe.
+/// </summary>
+public static class PipeAcl
+{
+    public static PipeSecurity Create(SecurityIdentifier allowedSid)
+    {
+        if (allowedSid is null) throw new ArgumentNullException(nameof(allowedSid));
+
+        var security = new PipeSecurity();
+
+        security.AddAccessRule(new PipeAccessRule(
+            allowedSid,
+            PipeAccessRights.ReadWrite | PipeAccessRights.Synchronize,
+            AccessControlType.Allow));
+
+        var localSystem = new SecurityIdentifier(WellKnownSidType.LocalSystemSid, null);
+        var admins      = new SecurityIdentifier(WellKnownSidType.BuiltinAdministratorsSid, null);
+
+        if (allowedSid != localSystem)
+            security.AddAccessRule(new PipeAccessRule(localSystem, PipeAccessRights.FullControl, AccessControlType.Deny));
+        if (allowedSid != admins)
+            security.AddAccessRule(new PipeAccessRule(admins,      PipeAccessRights.FullControl, AccessControlType.Deny));
+
+        security.SetOwner(allowedSid);
+
+        return security;
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Ipc/PipeServer.cs

@@ -0,0 +1,152 @@
+using System;
+using System.IO.Pipes;
+using System.Security.Principal;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+
+/// <summary>
+///     Accepts one client connection at a time on the FOCAS Host's named pipe with the
+///     strict ACL from <see cref="PipeAcl"/>. Verifies the peer SID + per-process shared
+///     secret before any RPC frame is accepted. Mirrors the Galaxy.Host pipe server byte for
+///     byte — different MessageKind enum, same negotiation semantics.
+/// </summary>
+public sealed class PipeServer : IDisposable
+{
+    private readonly string _pipeName;
+    private readonly SecurityIdentifier _allowedSid;
+    private readonly string _sharedSecret;
+    private readonly ILogger _logger;
+    private readonly CancellationTokenSource _cts = new();
+    private NamedPipeServerStream? _current;
+
+    public PipeServer(string pipeName, SecurityIdentifier allowedSid, string sharedSecret, ILogger logger)
+    {
+        _pipeName = pipeName ?? throw new ArgumentNullException(nameof(pipeName));
+        _allowedSid = allowedSid ?? throw new ArgumentNullException(nameof(allowedSid));
+        _sharedSecret = sharedSecret ?? throw new ArgumentNullException(nameof(sharedSecret));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    public async Task RunOneConnectionAsync(IFrameHandler handler, CancellationToken ct)
+    {
+        using var linked = CancellationTokenSource.CreateLinkedTokenSource(_cts.Token, ct);
+        var acl = PipeAcl.Create(_allowedSid);
+
+        _current = new NamedPipeServerStream(
+            _pipeName,
+            PipeDirection.InOut,
+            maxNumberOfServerInstances: 1,
+            PipeTransmissionMode.Byte,
+            PipeOptions.Asynchronous,
+            inBufferSize: 64 * 1024,
+            outBufferSize: 64 * 1024,
+            pipeSecurity: acl);
+
+        try
+        {
+            await _current.WaitForConnectionAsync(linked.Token).ConfigureAwait(false);
+
+            if (!VerifyCaller(_current, out var reason))
+            {
+                _logger.Warning("FOCAS IPC caller rejected: {Reason}", reason);
+                _current.Disconnect();
+                return;
+            }
+
+            using var reader = new FrameReader(_current, leaveOpen: true);
+            using var writer = new FrameWriter(_current, leaveOpen: true);
+
+            var first = await reader.ReadFrameAsync(linked.Token).ConfigureAwait(false);
+            if (first is null || first.Value.Kind != FocasMessageKind.Hello)
+            {
+                _logger.Warning("FOCAS IPC first frame was not Hello; dropping");
+                return;
+            }
+
+            var hello = MessagePackSerializer.Deserialize<Hello>(first.Value.Body);
+            if (!string.Equals(hello.SharedSecret, _sharedSecret, StringComparison.Ordinal))
+            {
+                await writer.WriteAsync(FocasMessageKind.HelloAck,
+                    new HelloAck { Accepted = false, RejectReason = "shared-secret-mismatch" },
+                    linked.Token).ConfigureAwait(false);
+                _logger.Warning("FOCAS IPC Hello rejected: shared-secret-mismatch");
+                return;
+            }
+
+            if (hello.ProtocolMajor != Hello.CurrentMajor)
+            {
+                await writer.WriteAsync(FocasMessageKind.HelloAck,
+                    new HelloAck
+                    {
+                        Accepted = false,
+                        RejectReason = $"major-version-mismatch-peer={hello.ProtocolMajor}-server={Hello.CurrentMajor}",
+                    },
+                    linked.Token).ConfigureAwait(false);
+                _logger.Warning("FOCAS IPC Hello rejected: major mismatch peer={Peer} server={Server}",
+                    hello.ProtocolMajor, Hello.CurrentMajor);
+                return;
+            }
+
+            await writer.WriteAsync(FocasMessageKind.HelloAck,
+                new HelloAck { Accepted = true, HostName = Environment.MachineName },
+                linked.Token).ConfigureAwait(false);
+
+            using var attachment = handler.AttachConnection(writer);
+
+            while (!linked.Token.IsCancellationRequested)
+            {
+                var frame = await reader.ReadFrameAsync(linked.Token).ConfigureAwait(false);
+                if (frame is null) break;
+
+                await handler.HandleAsync(frame.Value.Kind, frame.Value.Body, writer, linked.Token).ConfigureAwait(false);
+            }
+        }
+        finally
+        {
+            _current.Dispose();
+            _current = null;
+        }
+    }
+
+    public async Task RunAsync(IFrameHandler handler, CancellationToken ct)
+    {
+        while (!ct.IsCancellationRequested)
+        {
+            try { await RunOneConnectionAsync(handler, ct).ConfigureAwait(false); }
+            catch (OperationCanceledException) { break; }
+            catch (Exception ex) { _logger.Error(ex, "FOCAS IPC connection loop error — accepting next"); }
+        }
+    }
+
+    private bool VerifyCaller(NamedPipeServerStream pipe, out string reason)
+    {
+        try
+        {
+            pipe.RunAsClient(() =>
+            {
+                using var wi = WindowsIdentity.GetCurrent();
+                if (wi.User is null)
+                    throw new InvalidOperationException("GetCurrent().User is null — cannot verify caller");
+                if (wi.User != _allowedSid)
+                    throw new UnauthorizedAccessException(
+                        $"caller SID {wi.User.Value} does not match allowed {_allowedSid.Value}");
+            });
+            reason = string.Empty;
+            return true;
+        }
+        catch (Exception ex) { reason = ex.Message; return false; }
+    }
+
+    public void Dispose()
+    {
+        _cts.Cancel();
+        _current?.Dispose();
+        _cts.Dispose();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Ipc/StubFrameHandler.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+
+/// <summary>
+///     Placeholder handler that returns <c>ErrorResponse{Code=not-implemented}</c> for every
+///     FOCAS data-plane request. Exists so PR B can ship the pipe server + ACL + handshake
+///     plumbing before PR C moves the Fwlib32 calls. Heartbeats are handled fully so the
+///     supervisor's liveness detector stays happy.
+/// </summary>
+public sealed class StubFrameHandler : IFrameHandler
+{
+    public Task HandleAsync(FocasMessageKind kind, byte[] body, FrameWriter writer, CancellationToken ct)
+    {
+        if (kind == FocasMessageKind.Heartbeat)
+        {
+            var hb = MessagePackSerializer.Deserialize<Heartbeat>(body);
+            return writer.WriteAsync(FocasMessageKind.HeartbeatAck,
+                new HeartbeatAck
+                {
+                    MonotonicTicks = hb.MonotonicTicks,
+                    HostUtcUnixMs = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+                }, ct);
+        }
+
+        return writer.WriteAsync(FocasMessageKind.ErrorResponse,
+            new ErrorResponse
+            {
+                Code = "not-implemented",
+                Message = $"Kind {kind} is stubbed — Fwlib32 lift lands in PR C",
+            },
+            ct);
+    }
+
+    public IDisposable AttachConnection(FrameWriter writer) => IFrameHandler.NoopAttachment.Instance;
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/Program.cs

@@ -0,0 +1,72 @@
+using System;
+using System.Security.Principal;
+using System.Threading;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Backend;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host;
+
+/// <summary>
+///     Entry point for the <c>OtOpcUaFocasHost</c> Windows service / console host. The
+///     supervisor (Proxy-side) spawns this process per FOCAS driver instance and passes the
+///     pipe name, allowed-SID, and per-process shared secret as environment variables. In
+///     PR B the backend is <see cref="StubFrameHandler"/> — PR C swaps in the real
+///     Fwlib32-backed handler once the session state + STA thread move out of the .NET 10
+///     driver.
+/// </summary>
+public static class Program
+{
+    public static int Main(string[] args)
+    {
+        Log.Logger = new LoggerConfiguration()
+            .MinimumLevel.Information()
+            .WriteTo.File(
+                @"%ProgramData%\OtOpcUa\focas-host-.log".Replace("%ProgramData%", Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData)),
+                rollingInterval: RollingInterval.Day)
+            .CreateLogger();
+
+        try
+        {
+            var pipeName = Environment.GetEnvironmentVariable("OTOPCUA_FOCAS_PIPE") ?? "OtOpcUaFocas";
+            var allowedSidValue = Environment.GetEnvironmentVariable("OTOPCUA_ALLOWED_SID")
+                ?? throw new InvalidOperationException(
+                    "OTOPCUA_ALLOWED_SID not set — the FOCAS Proxy supervisor must pass the server principal SID");
+            var sharedSecret = Environment.GetEnvironmentVariable("OTOPCUA_FOCAS_SECRET")
+                ?? throw new InvalidOperationException(
+                    "OTOPCUA_FOCAS_SECRET not set — the FOCAS Proxy supervisor must pass the per-process secret at spawn time");
+
+            var allowedSid = new SecurityIdentifier(allowedSidValue);
+
+            using var server = new PipeServer(pipeName, allowedSid, sharedSecret, Log.Logger);
+            using var cts = new CancellationTokenSource();
+            Console.CancelKeyPress += (_, e) => { e.Cancel = true; cts.Cancel(); };
+
+            Log.Information("OtOpcUaFocasHost starting — pipe={Pipe} allowedSid={Sid}",
+                pipeName, allowedSidValue);
+
+            var backendKind = (Environment.GetEnvironmentVariable("OTOPCUA_FOCAS_BACKEND") ?? "unconfigured")
+                .ToLowerInvariant();
+            IFocasBackend backend = backendKind switch
+            {
+                "fake"         => new FakeFocasBackend(),
+                "unconfigured" => new UnconfiguredFocasBackend(),
+                "fwlib32"      => new UnconfiguredFocasBackend(), // real Fwlib32 backend lands with hardware integration follow-up
+                _              => new UnconfiguredFocasBackend(),
+            };
+            Log.Information("OtOpcUaFocasHost backend={Backend}", backendKind);
+
+            var handler = new FwlibFrameHandler(backend, Log.Logger);
+            server.RunAsync(handler, cts.Token).GetAwaiter().GetResult();
+
+            Log.Information("OtOpcUaFocasHost stopped cleanly");
+            return 0;
+        }
+        catch (Exception ex)
+        {
+            Log.Fatal(ex, "OtOpcUaFocasHost fatal");
+            return 2;
+        }
+        finally { Log.CloseAndFlush(); }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.csproj

@@ -0,0 +1,40 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net48</TargetFramework>
+        <!-- Fwlib32.dll is 32-bit only — x86 target is mandatory. Matches the Galaxy.Host
+             bitness constraint but for a different native library. -->
+        <PlatformTarget>x86</PlatformTarget>
+        <Prefer32Bit>true</Prefer32Bit>
+        <Nullable>enable</Nullable>
+        <LangVersion>latest</LangVersion>
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <NoWarn>$(NoWarn);CS1591</NoWarn>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host</RootNamespace>
+        <AssemblyName>OtOpcUa.Driver.FOCAS.Host</AssemblyName>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="System.IO.Pipes.AccessControl" Version="5.0.0"/>
+        <PackageReference Include="System.Memory" Version="4.5.5"/>
+        <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.4"/>
+        <PackageReference Include="Serilog" Version="4.2.0"/>
+        <PackageReference Include="Serilog.Sinks.File" Version="7.0.0"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+    </ItemGroup>
+
+</Project>

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/Addresses.cs

@@ -0,0 +1,39 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>
+///     Wire shape for a parsed FOCAS address. Mirrors <c>FocasAddress</c> in the driver
+///     package but lives in Shared so the Host (.NET 4.8) can decode without taking a
+///     reference to the .NET 10 driver assembly. The Proxy serializes from its own
+///     <c>FocasAddress</c>; the Host maps back to its local equivalent.
+/// </summary>
+[MessagePackObject]
+public sealed class FocasAddressDto
+{
+    /// <summary>0 = Pmc, 1 = Parameter, 2 = Macro. Matches <c>FocasAreaKind</c> enum order.</summary>
+    [Key(0)] public int Kind { get; set; }
+
+    /// <summary>PMC letter — null for Parameter / Macro.</summary>
+    [Key(1)] public string? PmcLetter { get; set; }
+
+    [Key(2)] public int Number { get; set; }
+
+    /// <summary>Optional bit index (0-7 for PMC, 0-31 for Parameter).</summary>
+    [Key(3)] public int? BitIndex { get; set; }
+}
+
+/// <summary>
+///     0 = Bit, 1 = Byte, 2 = Int16, 3 = Int32, 4 = Float32, 5 = Float64, 6 = String.
+///     Matches <c>FocasDataType</c> enum order so both sides can cast <c>(int)</c>.
+/// </summary>
+public static class FocasDataTypeCode
+{
+    public const int Bit = 0;
+    public const int Byte = 1;
+    public const int Int16 = 2;
+    public const int Int32 = 3;
+    public const int Float32 = 4;
+    public const int Float64 = 5;
+    public const int String = 6;
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/Framing.cs

@@ -0,0 +1,57 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>
+///     Length-prefixed framing. Each IPC frame is:
+///     <c>[4-byte big-endian length][1-byte message kind][MessagePack body]</c>.
+///     Length is the body size only; the kind byte is not part of the prefixed length.
+///     Mirrors the Galaxy Tier-C framing so operators see one wire format across hosts.
+/// </summary>
+public static class Framing
+{
+    public const int LengthPrefixSize = 4;
+    public const int KindByteSize = 1;
+
+    /// <summary>
+    ///     Maximum permitted body length (16 MiB). Protects the receiver from a hostile or
+    ///     misbehaving peer sending an oversized length prefix.
+    /// </summary>
+    public const int MaxFrameBodyBytes = 16 * 1024 * 1024;
+}
+
+/// <summary>
+///     Wire identifier for each contract. Values are stable — new contracts append, never
+///     reuse. Ranges kept aligned with Galaxy so an operator reading a hex dump doesn't have
+///     to context-switch between drivers.
+/// </summary>
+public enum FocasMessageKind : byte
+{
+    Hello                    = 0x01,
+    HelloAck                 = 0x02,
+    Heartbeat                = 0x03,
+    HeartbeatAck             = 0x04,
+
+    OpenSessionRequest       = 0x10,
+    OpenSessionResponse      = 0x11,
+    CloseSessionRequest      = 0x12,
+
+    ReadRequest              = 0x30,
+    ReadResponse             = 0x31,
+    WriteRequest             = 0x32,
+    WriteResponse            = 0x33,
+    PmcBitWriteRequest       = 0x34,
+    PmcBitWriteResponse      = 0x35,
+
+    SubscribeRequest         = 0x40,
+    SubscribeResponse        = 0x41,
+    UnsubscribeRequest       = 0x42,
+    OnDataChangeNotification = 0x43,
+
+    ProbeRequest             = 0x70,
+    ProbeResponse            = 0x71,
+    RuntimeStatusChange      = 0x72,
+
+    RecycleHostRequest       = 0xF0,
+    RecycleStatusResponse    = 0xF1,
+
+    ErrorResponse            = 0xFE,
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/Hello.cs

@@ -0,0 +1,63 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>
+///     First frame of every FOCAS Proxy -> Host connection. Advertises protocol major/minor
+///     and the per-process shared secret the Proxy passed to the Host at spawn time. Major
+///     mismatch is fatal; minor is advisory.
+/// </summary>
+[MessagePackObject]
+public sealed class Hello
+{
+    public const int CurrentMajor = 1;
+    public const int CurrentMinor = 0;
+
+    [Key(0)] public int ProtocolMajor { get; set; } = CurrentMajor;
+    [Key(1)] public int ProtocolMinor { get; set; } = CurrentMinor;
+    [Key(2)] public string PeerName { get; set; } = string.Empty;
+
+    /// <summary>
+    ///     Per-process shared secret verified on the Host side against the value passed by the
+    ///     supervisor at spawn time. Protects against a local attacker connecting to the pipe
+    ///     after authenticating via the pipe ACL.
+    /// </summary>
+    [Key(3)] public string SharedSecret { get; set; } = string.Empty;
+
+    [Key(4)] public string[] Features { get; set; } = System.Array.Empty<string>();
+}
+
+[MessagePackObject]
+public sealed class HelloAck
+{
+    [Key(0)] public int ProtocolMajor { get; set; } = Hello.CurrentMajor;
+    [Key(1)] public int ProtocolMinor { get; set; } = Hello.CurrentMinor;
+
+    /// <summary>True if the Host accepted the hello; false + <see cref="RejectReason"/> filled if not.</summary>
+    [Key(2)] public bool Accepted { get; set; }
+    [Key(3)] public string? RejectReason { get; set; }
+
+    [Key(4)] public string HostName { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class Heartbeat
+{
+    [Key(0)] public long MonotonicTicks { get; set; }
+}
+
+[MessagePackObject]
+public sealed class HeartbeatAck
+{
+    [Key(0)] public long MonotonicTicks { get; set; }
+    [Key(1)] public long HostUtcUnixMs { get; set; }
+}
+
+[MessagePackObject]
+public sealed class ErrorResponse
+{
+    /// <summary>Stable symbolic code — e.g. <c>InvalidAddress</c>, <c>SessionNotFound</c>, <c>Fwlib32Crashed</c>.</summary>
+    [Key(0)] public string Code { get; set; } = string.Empty;
+
+    [Key(1)] public string Message { get; set; } = string.Empty;
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/Probe.cs

@@ -0,0 +1,47 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>Lightweight connectivity probe — maps to <c>cnc_rdcncstat</c> on the Host.</summary>
+[MessagePackObject]
+public sealed class ProbeRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public int TimeoutMs { get; set; } = 2000;
+}
+
+[MessagePackObject]
+public sealed class ProbeResponse
+{
+    [Key(0)] public bool Healthy { get; set; }
+    [Key(1)] public string? Error { get; set; }
+    [Key(2)] public long ObservedAtUtcUnixMs { get; set; }
+}
+
+/// <summary>Per-host runtime status — fan-out target when the Host observes the CNC going unreachable without the Proxy asking.</summary>
+[MessagePackObject]
+public sealed class RuntimeStatusChangeNotification
+{
+    [Key(0)] public long SessionId { get; set; }
+
+    /// <summary>Running | Stopped | Unknown.</summary>
+    [Key(1)] public string RuntimeStatus { get; set; } = string.Empty;
+
+    [Key(2)] public long ObservedAtUtcUnixMs { get; set; }
+}
+
+[MessagePackObject]
+public sealed class RecycleHostRequest
+{
+    /// <summary>Soft | Hard. Soft drains subscriptions first; Hard kills immediately.</summary>
+    [Key(0)] public string Kind { get; set; } = "Soft";
+    [Key(1)] public string Reason { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class RecycleStatusResponse
+{
+    [Key(0)] public bool Accepted { get; set; }
+    [Key(1)] public int GraceSeconds { get; set; } = 15;
+    [Key(2)] public string? Error { get; set; }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/ReadWrite.cs

@@ -0,0 +1,85 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>
+///     Read one FOCAS address. Multi-read is the Proxy's responsibility — it batches
+///     per-tag reads into parallel <see cref="ReadRequest"/> frames the Host services on its
+///     STA thread. Keeping the IPC read single-address keeps the Host side trivial; FOCAS
+///     itself has no multi-read primitive that spans area kinds.
+/// </summary>
+[MessagePackObject]
+public sealed class ReadRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public FocasAddressDto Address { get; set; } = new();
+    [Key(2)] public int DataType { get; set; }
+    [Key(3)] public int TimeoutMs { get; set; } = 2000;
+}
+
+[MessagePackObject]
+public sealed class ReadResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+
+    /// <summary>OPC UA status code mapped by the Host via <c>FocasStatusMapper</c> — 0 = Good.</summary>
+    [Key(2)] public uint StatusCode { get; set; }
+
+    /// <summary>MessagePack-serialized boxed value. <c>null</c> when <see cref="Success"/> is false.</summary>
+    [Key(3)] public byte[]? ValueBytes { get; set; }
+
+    /// <summary>Matches <see cref="FocasDataTypeCode"/> so the Proxy knows how to deserialize.</summary>
+    [Key(4)] public int ValueTypeCode { get; set; }
+
+    [Key(5)] public long SourceTimestampUtcUnixMs { get; set; }
+}
+
+[MessagePackObject]
+public sealed class WriteRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public FocasAddressDto Address { get; set; } = new();
+    [Key(2)] public int DataType { get; set; }
+    [Key(3)] public byte[]? ValueBytes { get; set; }
+    [Key(4)] public int ValueTypeCode { get; set; }
+    [Key(5)] public int TimeoutMs { get; set; } = 2000;
+}
+
+[MessagePackObject]
+public sealed class WriteResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+
+    /// <summary>OPC UA status code — 0 = Good.</summary>
+    [Key(2)] public uint StatusCode { get; set; }
+}
+
+/// <summary>
+///     PMC bit read-modify-write. Handled as a first-class operation (not two separate
+///     read+write round-trips) so the critical section stays on the Host — serializing
+///     concurrent bit writers to the same parent byte is Host-side via
+///     <c>SemaphoreSlim</c> keyed on <c>(PmcLetter, Number)</c>. Mirrors the in-process
+///     pattern from <c>FocasPmcBitRmw</c>.
+/// </summary>
+[MessagePackObject]
+public sealed class PmcBitWriteRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public FocasAddressDto Address { get; set; } = new();
+
+    /// <summary>The bit index to set/clear. 0-7.</summary>
+    [Key(2)] public int BitIndex { get; set; }
+
+    [Key(3)] public bool Value { get; set; }
+    [Key(4)] public int TimeoutMs { get; set; } = 2000;
+}
+
+[MessagePackObject]
+public sealed class PmcBitWriteResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+    [Key(2)] public uint StatusCode { get; set; }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/Session.cs

@@ -0,0 +1,31 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>
+///     Open a FOCAS session against the CNC at <see cref="HostAddress"/>. One session per
+///     configured device. The Host owns the Fwlib32 handle; the Proxy tracks only the
+///     opaque <see cref="OpenSessionResponse.SessionId"/> returned on success.
+/// </summary>
+[MessagePackObject]
+public sealed class OpenSessionRequest
+{
+    [Key(0)] public string HostAddress { get; set; } = string.Empty;
+    [Key(1)] public int TimeoutMs { get; set; } = 2000;
+    [Key(2)] public int CncSeries { get; set; }
+}
+
+[MessagePackObject]
+public sealed class OpenSessionResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public long SessionId { get; set; }
+    [Key(2)] public string? Error { get; set; }
+    [Key(3)] public string? ErrorCode { get; set; }
+}
+
+[MessagePackObject]
+public sealed class CloseSessionRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/Subscriptions.cs

@@ -0,0 +1,61 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>
+///     Subscribe the Host to polling a set of tags on behalf of the Proxy. FOCAS is
+///     poll-only — there are no CNC-initiated callbacks — so the Host runs the poll loop and
+///     pushes <see cref="OnDataChangeNotification"/> frames whenever a value differs from
+///     the last observation. Delta-only + per-group interval keeps the wire quiet.
+/// </summary>
+[MessagePackObject]
+public sealed class SubscribeRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public long SubscriptionId { get; set; }
+    [Key(2)] public int IntervalMs { get; set; } = 1000;
+    [Key(3)] public SubscribeItem[] Items { get; set; } = System.Array.Empty<SubscribeItem>();
+}
+
+[MessagePackObject]
+public sealed class SubscribeItem
+{
+    /// <summary>Opaque correlation id the Proxy uses to route notifications back to the right OPC UA MonitoredItem.</summary>
+    [Key(0)] public long MonitoredItemId { get; set; }
+
+    [Key(1)] public FocasAddressDto Address { get; set; } = new();
+    [Key(2)] public int DataType { get; set; }
+}
+
+[MessagePackObject]
+public sealed class SubscribeResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+
+    /// <summary>Items the Host refused (address mismatch, unsupported type). Empty on full success.</summary>
+    [Key(2)] public long[] RejectedMonitoredItemIds { get; set; } = System.Array.Empty<long>();
+}
+
+[MessagePackObject]
+public sealed class UnsubscribeRequest
+{
+    [Key(0)] public long SubscriptionId { get; set; }
+}
+
+[MessagePackObject]
+public sealed class OnDataChangeNotification
+{
+    [Key(0)] public long SubscriptionId { get; set; }
+    [Key(1)] public DataChange[] Changes { get; set; } = System.Array.Empty<DataChange>();
+}
+
+[MessagePackObject]
+public sealed class DataChange
+{
+    [Key(0)] public long MonitoredItemId { get; set; }
+    [Key(1)] public uint StatusCode { get; set; }
+    [Key(2)] public byte[]? ValueBytes { get; set; }
+    [Key(3)] public int ValueTypeCode { get; set; }
+    [Key(4)] public long SourceTimestampUtcUnixMs { get; set; }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/FrameReader.cs

@@ -0,0 +1,67 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+
+/// <summary>
+///     Reads length-prefixed, kind-tagged frames from a stream. Single-consumer — do not call
+///     <see cref="ReadFrameAsync"/> from multiple threads against the same instance.
+/// </summary>
+public sealed class FrameReader : IDisposable
+{
+    private readonly Stream _stream;
+    private readonly bool _leaveOpen;
+
+    public FrameReader(Stream stream, bool leaveOpen = false)
+    {
+        _stream = stream ?? throw new ArgumentNullException(nameof(stream));
+        _leaveOpen = leaveOpen;
+    }
+
+    public async Task<(FocasMessageKind Kind, byte[] Body)?> ReadFrameAsync(CancellationToken ct)
+    {
+        var lengthPrefix = new byte[Framing.LengthPrefixSize];
+        if (!await ReadExactAsync(lengthPrefix, ct).ConfigureAwait(false))
+            return null;
+
+        var length = (lengthPrefix[0] << 24) | (lengthPrefix[1] << 16) | (lengthPrefix[2] << 8) | lengthPrefix[3];
+        if (length < 0 || length > Framing.MaxFrameBodyBytes)
+            throw new InvalidDataException($"IPC frame length {length} out of range.");
+
+        var kindByte = _stream.ReadByte();
+        if (kindByte < 0) throw new EndOfStreamException("EOF after length prefix, before kind byte.");
+
+        var body = new byte[length];
+        if (!await ReadExactAsync(body, ct).ConfigureAwait(false))
+            throw new EndOfStreamException("EOF mid-frame.");
+
+        return ((FocasMessageKind)(byte)kindByte, body);
+    }
+
+    public static T Deserialize<T>(byte[] body) => MessagePackSerializer.Deserialize<T>(body);
+
+    private async Task<bool> ReadExactAsync(byte[] buffer, CancellationToken ct)
+    {
+        var offset = 0;
+        while (offset < buffer.Length)
+        {
+            var read = await _stream.ReadAsync(buffer, offset, buffer.Length - offset, ct).ConfigureAwait(false);
+            if (read == 0)
+            {
+                if (offset == 0) return false;
+                throw new EndOfStreamException($"Stream ended after reading {offset} of {buffer.Length} bytes.");
+            }
+            offset += read;
+        }
+        return true;
+    }
+
+    public void Dispose()
+    {
+        if (!_leaveOpen) _stream.Dispose();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/FrameWriter.cs

@@ -0,0 +1,56 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+
+/// <summary>
+///     Writes length-prefixed, kind-tagged MessagePack frames to a stream. Thread-safe via
+///     <see cref="SemaphoreSlim"/> — multiple producers (e.g. heartbeat + data-plane sharing a
+///     stream) get serialized writes.
+/// </summary>
+public sealed class FrameWriter : IDisposable
+{
+    private readonly Stream _stream;
+    private readonly SemaphoreSlim _gate = new(1, 1);
+    private readonly bool _leaveOpen;
+
+    public FrameWriter(Stream stream, bool leaveOpen = false)
+    {
+        _stream = stream ?? throw new ArgumentNullException(nameof(stream));
+        _leaveOpen = leaveOpen;
+    }
+
+    public async Task WriteAsync<T>(FocasMessageKind kind, T message, CancellationToken ct)
+    {
+        var body = MessagePackSerializer.Serialize(message, cancellationToken: ct);
+        if (body.Length > Framing.MaxFrameBodyBytes)
+            throw new InvalidOperationException(
+                $"IPC frame body {body.Length} exceeds {Framing.MaxFrameBodyBytes} byte cap.");
+
+        var lengthPrefix = new byte[Framing.LengthPrefixSize];
+        lengthPrefix[0] = (byte)((body.Length >> 24) & 0xFF);
+        lengthPrefix[1] = (byte)((body.Length >> 16) & 0xFF);
+        lengthPrefix[2] = (byte)((body.Length >> 8)  & 0xFF);
+        lengthPrefix[3] = (byte)( body.Length        & 0xFF);
+
+        await _gate.WaitAsync(ct).ConfigureAwait(false);
+        try
+        {
+            await _stream.WriteAsync(lengthPrefix, 0, lengthPrefix.Length, ct).ConfigureAwait(false);
+            _stream.WriteByte((byte)kind);
+            await _stream.WriteAsync(body, 0, body.Length, ct).ConfigureAwait(false);
+            await _stream.FlushAsync(ct).ConfigureAwait(false);
+        }
+        finally { _gate.Release(); }
+    }
+
+    public void Dispose()
+    {
+        _gate.Dispose();
+        if (!_leaveOpen) _stream.Dispose();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>netstandard2.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <LangVersion>latest</LangVersion>
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <NoWarn>$(NoWarn);CS1591</NoWarn>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <!-- MessagePack for IPC. Netstandard 2.0 consumable by both .NET 10 (Proxy) + .NET 4.8 (Host). -->
+        <PackageReference Include="MessagePack" Version="2.5.187"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+    </ItemGroup>
+
+</Project>

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCapabilityMatrix.cs

@@ -0,0 +1,139 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     Documented-API capability matrix — per CNC series, what ranges each
+///     <see cref="FocasAreaKind"/> supports. Authoritative source for the driver's
+///     pre-flight validation in <see cref="FocasDriver.InitializeAsync"/>.
+/// </summary>
+/// <remarks>
+///     <para>Ranges come from the Fanuc FOCAS Developer Kit documentation matrix
+///     (see <c>docs/v2/focas-version-matrix.md</c> for the authoritative copy with
+///     per-function citations). Numbers chosen to match what the FOCAS library
+///     accepts — a read against an address outside the documented range returns
+///     <c>EW_NUMBER</c> or <c>EW_PARAM</c> at the wire, which this driver maps to
+///     BadOutOfRange. Catching at init time surfaces the mismatch as a config
+///     error before any session is opened.</para>
+///     <para><see cref="FocasCncSeries.Unknown"/> is treated permissively: every
+///     address passes validation. Pre-matrix configs don't break on upgrade; new
+///     deployments are encouraged to declare a series in the device options.</para>
+/// </remarks>
+public static class FocasCapabilityMatrix
+{
+    /// <summary>
+    ///     Check whether <paramref name="address"/> is accepted by a CNC of
+    ///     <paramref name="series"/>. Returns <c>null</c> on pass + a failure reason
+    ///     on reject — the driver surfaces the reason string verbatim when failing
+    ///     <c>InitializeAsync</c> so operators see the specific out-of-range without
+    ///     guessing.
+    /// </summary>
+    public static string? Validate(FocasCncSeries series, FocasAddress address)
+    {
+        if (series == FocasCncSeries.Unknown) return null;
+
+        return address.Kind switch
+        {
+            FocasAreaKind.Macro     => ValidateMacro(series, address.Number),
+            FocasAreaKind.Parameter => ValidateParameter(series, address.Number),
+            FocasAreaKind.Pmc       => ValidatePmc(series, address.PmcLetter, address.Number),
+            _ => null,
+        };
+    }
+
+    /// <summary>Macro variable number accepted by a CNC series. Cites
+    /// <c>cnc_rdmacro</c>/<c>cnc_wrmacro</c> in the Developer Kit.</summary>
+    internal static (int min, int max) MacroRange(FocasCncSeries series) => series switch
+    {
+        // Common macros 1-33 + 100-199 + 500-999 universally; extended 10000+ only on
+        // higher-end series. Using the extended ceiling per series per DevKit notes.
+        FocasCncSeries.Sixteen_i    => (0, 999),
+        FocasCncSeries.Zero_i_D     => (0, 999),
+        FocasCncSeries.Zero_i_F or
+        FocasCncSeries.Zero_i_MF or
+        FocasCncSeries.Zero_i_TF    => (0, 9999),
+        FocasCncSeries.Thirty_i or
+        FocasCncSeries.ThirtyOne_i or
+        FocasCncSeries.ThirtyTwo_i  => (0, 99999),
+        FocasCncSeries.PowerMotion_i => (0, 999),
+        _ => (0, int.MaxValue),
+    };
+
+    /// <summary>Parameter number accepted; from <c>cnc_rdparam</c>/<c>cnc_wrparam</c>.
+    /// Ranges reflect the highest-numbered parameter documented per series.</summary>
+    internal static (int min, int max) ParameterRange(FocasCncSeries series) => series switch
+    {
+        FocasCncSeries.Sixteen_i    => (0, 9999),
+        FocasCncSeries.Zero_i_D or
+        FocasCncSeries.Zero_i_F or
+        FocasCncSeries.Zero_i_MF or
+        FocasCncSeries.Zero_i_TF    => (0, 14999),
+        FocasCncSeries.Thirty_i or
+        FocasCncSeries.ThirtyOne_i or
+        FocasCncSeries.ThirtyTwo_i  => (0, 29999),
+        FocasCncSeries.PowerMotion_i => (0, 29999),
+        _ => (0, int.MaxValue),
+    };
+
+    /// <summary>PMC letters accepted per series. Legacy controllers omit F/M/C
+    /// signal groups that 30i-family ladder programs use.</summary>
+    internal static IReadOnlySet<string> PmcLetters(FocasCncSeries series) => series switch
+    {
+        FocasCncSeries.Sixteen_i     => new HashSet<string>(StringComparer.OrdinalIgnoreCase) { "X", "Y", "R", "D" },
+        FocasCncSeries.Zero_i_D      => new HashSet<string>(StringComparer.OrdinalIgnoreCase) { "X", "Y", "R", "D", "E", "A" },
+        FocasCncSeries.Zero_i_F or
+        FocasCncSeries.Zero_i_MF or
+        FocasCncSeries.Zero_i_TF     => new HashSet<string>(StringComparer.OrdinalIgnoreCase) { "X", "Y", "F", "G", "R", "D", "E", "A", "M", "C" },
+        FocasCncSeries.Thirty_i or
+        FocasCncSeries.ThirtyOne_i or
+        FocasCncSeries.ThirtyTwo_i   => new HashSet<string>(StringComparer.OrdinalIgnoreCase) { "X", "Y", "F", "G", "R", "D", "E", "A", "M", "C", "K", "T" },
+        FocasCncSeries.PowerMotion_i => new HashSet<string>(StringComparer.OrdinalIgnoreCase) { "X", "Y", "R", "D" },
+        _ => new HashSet<string>(StringComparer.OrdinalIgnoreCase),
+    };
+
+    /// <summary>PMC address-number ceiling per series. Multiplied by 8 to get bit
+    /// count since PMC addresses are byte-addressed on read + bit-addressed on
+    /// write — FocasAddress carries the bit separately.</summary>
+    internal static int PmcMaxNumber(FocasCncSeries series) => series switch
+    {
+        FocasCncSeries.Sixteen_i    => 999,
+        FocasCncSeries.Zero_i_D     => 1999,
+        FocasCncSeries.Zero_i_F or
+        FocasCncSeries.Zero_i_MF or
+        FocasCncSeries.Zero_i_TF    => 9999,
+        FocasCncSeries.Thirty_i or
+        FocasCncSeries.ThirtyOne_i or
+        FocasCncSeries.ThirtyTwo_i  => 59999,
+        FocasCncSeries.PowerMotion_i => 1999,
+        _ => int.MaxValue,
+    };
+
+    private static string? ValidateMacro(FocasCncSeries series, int number)
+    {
+        var (min, max) = MacroRange(series);
+        return (number < min || number > max)
+            ? $"Macro variable #{number} is outside the documented range [{min}, {max}] for {series}."
+            : null;
+    }
+
+    private static string? ValidateParameter(FocasCncSeries series, int number)
+    {
+        var (min, max) = ParameterRange(series);
+        return (number < min || number > max)
+            ? $"Parameter #{number} is outside the documented range [{min}, {max}] for {series}."
+            : null;
+    }
+
+    private static string? ValidatePmc(FocasCncSeries series, string? letter, int number)
+    {
+        if (string.IsNullOrEmpty(letter)) return "PMC address is missing its letter prefix.";
+        var letters = PmcLetters(series);
+        if (!letters.Contains(letter))
+        {
+            var letterList = string.Join(", ", letters);
+            return $"PMC letter '{letter}' is not supported on {series}. Accepted: {{{letterList}}}.";
+        }
+        var max = PmcMaxNumber(series);
+        return number > max
+            ? $"PMC address {letter}{number} is outside the documented range [0, {max}] for {series}."
+            : null;
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCncSeries.cs

@@ -0,0 +1,47 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     Fanuc CNC controller series. Used by <see cref="FocasCapabilityMatrix"/> to
+///     gate which FOCAS addresses + value ranges the driver accepts against a given
+///     CNC — the FOCAS API surface varies meaningfully between series (macro ranges,
+///     PMC address letters, parameter numbers). A tag reference that's valid on a
+///     30i might be out-of-range on an 0i-MF; validating at driver
+///     <c>InitializeAsync</c> time surfaces the mismatch as a fast config error
+///     instead of a runtime read failure after the server's already running.
+/// </summary>
+/// <remarks>
+///     <para>Values chosen from the Fanuc FOCAS Developer Kit documented series
+///     matrix. Add a new entry + a row to <see cref="FocasCapabilityMatrix"/> when
+///     a new controller is targeted — the driver will refuse the device until both
+///     sides of the enum are filled in.</para>
+///     <para>Defaults to <see cref="Unknown"/> when the operator doesn't specify;
+///     the capability matrix treats Unknown as permissive (no range validation,
+///     same as pre-matrix behaviour) so old configs don't break on upgrade.</para>
+/// </remarks>
+public enum FocasCncSeries
+{
+    /// <summary>No series declared; capability matrix is permissive (legacy behaviour).</summary>
+    Unknown = 0,
+
+    /// <summary>Series 0i-D — compact CNC, narrow macro + PMC ranges.</summary>
+    Zero_i_D,
+    /// <summary>Series 0i-F — successor to 0i-D; widened macro range, added Plus variant.</summary>
+    Zero_i_F,
+    /// <summary>Series 0i-MF / 0i-MF Plus — machining-centre variants of 0i-F.</summary>
+    Zero_i_MF,
+    /// <summary>Series 0i-TF / 0i-TF Plus — turning-centre variants of 0i-F.</summary>
+    Zero_i_TF,
+
+    /// <summary>Series 16i / 18i / 21i — mid-range legacy; narrow ranges, limited PMC letters.</summary>
+    Sixteen_i,
+
+    /// <summary>Series 30i — high-end; widest macro / PMC / parameter ranges.</summary>
+    Thirty_i,
+    /// <summary>Series 31i — subset of 30i (fewer axes, same FOCAS surface).</summary>
+    ThirtyOne_i,
+    /// <summary>Series 32i — compact 30i variant.</summary>
+    ThirtyTwo_i,
+
+    /// <summary>Power Motion i — motion-control variant; atypical macro coverage.</summary>
+    PowerMotion_i,
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs

@@ -57,7 +57,24 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                         $"FOCAS device has invalid HostAddress '{device.HostAddress}' — expected 'focas://{{ip}}[:{{port}}]'.");
                 _devices[device.HostAddress] = new DeviceState(addr, device);
             }
-            foreach (var tag in _options.Tags) _tagsByName[tag.Name] = tag;
+            // Pre-flight: validate every tag's address against the declared CNC
+            // series so misconfigured addresses fail at init (clear config error)
+            // instead of producing BadOutOfRange on every read at runtime.
+            // Series=Unknown short-circuits the matrix; pre-matrix configs stay permissive.
+            foreach (var tag in _options.Tags)
+            {
+                var parsed = FocasAddress.TryParse(tag.Address)
+                    ?? throw new InvalidOperationException(
+                        $"FOCAS tag '{tag.Name}' has invalid Address '{tag.Address}'. " +
+                        $"Expected forms: R100, R100.3, PARAM:1815/0, MACRO:500.");
+                if (_devices.TryGetValue(tag.DeviceHostAddress, out var device)
+                    && FocasCapabilityMatrix.Validate(device.Options.Series, parsed) is { } reason)
+                {
+                    throw new InvalidOperationException(
+                        $"FOCAS tag '{tag.Name}' ({tag.Address}) rejected by capability matrix: {reason}");
+                }
+                _tagsByName[tag.Name] = tag;
+            }
 
             if (_options.Probe.Enabled)
             {

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriverOptions.cs

@@ -13,9 +13,15 @@ public sealed class FocasDriverOptions
     public TimeSpan Timeout { get; init; } = TimeSpan.FromSeconds(2);
 }
 
+/// <summary>
+///     One CNC the driver talks to. <paramref name="Series"/> enables per-series
+///     address validation at <see cref="FocasDriver.InitializeAsync"/>; leave as
+///     <see cref="FocasCncSeries.Unknown"/> to skip validation (legacy behaviour).
+/// </summary>
 public sealed record FocasDeviceOptions(
     string HostAddress,
-    string? DeviceName = null);
+    string? DeviceName = null,
+    FocasCncSeries Series = FocasCncSeries.Unknown);
 
 /// <summary>
 ///     One FOCAS-backed OPC UA variable. <paramref name="Address"/> is the canonical FOCAS

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/Ipc/FocasIpcClient.cs

@@ -0,0 +1,120 @@
+using System.IO;
+using System.IO.Pipes;
+using MessagePack;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Ipc;
+
+/// <summary>
+///     Proxy-side IPC channel to a running <c>Driver.FOCAS.Host</c>. Owns the pipe connection
+///     and serializes request/response round-trips through a single call gate so
+///     concurrent callers don't interleave frames. One instance per FOCAS Host session.
+/// </summary>
+public sealed class FocasIpcClient : IAsyncDisposable
+{
+    private readonly Stream _stream;
+    private readonly FrameReader _reader;
+    private readonly FrameWriter _writer;
+    private readonly SemaphoreSlim _callGate = new(1, 1);
+
+    private FocasIpcClient(Stream stream)
+    {
+        _stream = stream;
+        _reader = new FrameReader(stream, leaveOpen: true);
+        _writer = new FrameWriter(stream, leaveOpen: true);
+    }
+
+    /// <summary>Named-pipe factory: connects, sends Hello, awaits HelloAck.</summary>
+    public static async Task<FocasIpcClient> ConnectAsync(
+        string pipeName, string sharedSecret, TimeSpan connectTimeout, CancellationToken ct)
+    {
+        var stream = new NamedPipeClientStream(
+            serverName: ".",
+            pipeName: pipeName,
+            direction: PipeDirection.InOut,
+            options: PipeOptions.Asynchronous);
+
+        await stream.ConnectAsync((int)connectTimeout.TotalMilliseconds, ct);
+        return await HandshakeAsync(stream, sharedSecret, ct).ConfigureAwait(false);
+    }
+
+    /// <summary>
+    ///     Stream factory — used by tests that wire the Proxy against an in-memory stream
+    ///     pair instead of a real pipe. <paramref name="stream"/> is owned by the caller
+    ///     until <see cref="DisposeAsync"/>.
+    /// </summary>
+    public static Task<FocasIpcClient> ConnectAsync(Stream stream, string sharedSecret, CancellationToken ct)
+        => HandshakeAsync(stream, sharedSecret, ct);
+
+    private static async Task<FocasIpcClient> HandshakeAsync(Stream stream, string sharedSecret, CancellationToken ct)
+    {
+        var client = new FocasIpcClient(stream);
+        try
+        {
+            await client._writer.WriteAsync(FocasMessageKind.Hello,
+                new Hello { PeerName = "FOCAS.Proxy", SharedSecret = sharedSecret }, ct).ConfigureAwait(false);
+
+            var ack = await client._reader.ReadFrameAsync(ct).ConfigureAwait(false);
+            if (ack is null || ack.Value.Kind != FocasMessageKind.HelloAck)
+                throw new InvalidOperationException("Did not receive HelloAck from FOCAS.Host");
+
+            var ackMsg = FrameReader.Deserialize<HelloAck>(ack.Value.Body);
+            if (!ackMsg.Accepted)
+                throw new UnauthorizedAccessException($"FOCAS.Host rejected Hello: {ackMsg.RejectReason}");
+
+            return client;
+        }
+        catch
+        {
+            await client.DisposeAsync().ConfigureAwait(false);
+            throw;
+        }
+    }
+
+    public async Task<TResp> CallAsync<TReq, TResp>(
+        FocasMessageKind requestKind, TReq request, FocasMessageKind expectedResponseKind, CancellationToken ct)
+    {
+        await _callGate.WaitAsync(ct).ConfigureAwait(false);
+        try
+        {
+            await _writer.WriteAsync(requestKind, request, ct).ConfigureAwait(false);
+
+            var frame = await _reader.ReadFrameAsync(ct).ConfigureAwait(false);
+            if (frame is null) throw new EndOfStreamException("FOCAS IPC peer closed before response");
+
+            if (frame.Value.Kind == FocasMessageKind.ErrorResponse)
+            {
+                var err = MessagePackSerializer.Deserialize<ErrorResponse>(frame.Value.Body);
+                throw new FocasIpcException(err.Code, err.Message);
+            }
+
+            if (frame.Value.Kind != expectedResponseKind)
+                throw new InvalidOperationException(
+                    $"Expected {expectedResponseKind}, got {frame.Value.Kind}");
+
+            return MessagePackSerializer.Deserialize<TResp>(frame.Value.Body);
+        }
+        finally { _callGate.Release(); }
+    }
+
+    public async Task SendOneWayAsync<TReq>(FocasMessageKind requestKind, TReq request, CancellationToken ct)
+    {
+        await _callGate.WaitAsync(ct).ConfigureAwait(false);
+        try { await _writer.WriteAsync(requestKind, request, ct).ConfigureAwait(false); }
+        finally { _callGate.Release(); }
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        _callGate.Dispose();
+        _reader.Dispose();
+        _writer.Dispose();
+        await _stream.DisposeAsync().ConfigureAwait(false);
+    }
+}
+
+public sealed class FocasIpcException(string code, string message) : Exception($"[{code}] {message}")
+{
+    public string Code { get; } = code;
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/Ipc/IpcFocasClient.cs

@@ -0,0 +1,199 @@
+using MessagePack;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Ipc;
+
+/// <summary>
+///     <see cref="IFocasClient"/> implementation that forwards every operation over a
+///     <see cref="FocasIpcClient"/> to a <c>Driver.FOCAS.Host</c> process. Keeps the
+///     <c>Fwlib32.dll</c> P/Invoke out of the main server process so a native crash
+///     blast-radius stops at the Host boundary.
+/// </summary>
+/// <remarks>
+///     Session lifecycle: <see cref="ConnectAsync"/> sends <c>OpenSessionRequest</c> and
+///     caches the returned <c>SessionId</c>. Subsequent <see cref="ReadAsync"/> /
+///     <see cref="WriteAsync"/> / <see cref="ProbeAsync"/> calls thread that session id
+///     onto each request DTO. <see cref="Dispose"/> sends <c>CloseSessionRequest</c> +
+///     disposes the underlying pipe.
+/// </remarks>
+public sealed class IpcFocasClient : IFocasClient
+{
+    private readonly FocasIpcClient _ipc;
+    private readonly FocasCncSeries _series;
+    private long _sessionId;
+    private bool _connected;
+
+    public IpcFocasClient(FocasIpcClient ipc, FocasCncSeries series = FocasCncSeries.Unknown)
+    {
+        _ipc = ipc ?? throw new ArgumentNullException(nameof(ipc));
+        _series = series;
+    }
+
+    public bool IsConnected => _connected;
+
+    public async Task ConnectAsync(FocasHostAddress address, TimeSpan timeout, CancellationToken cancellationToken)
+    {
+        if (_connected) return;
+
+        var resp = await _ipc.CallAsync<OpenSessionRequest, OpenSessionResponse>(
+            FocasMessageKind.OpenSessionRequest,
+            new OpenSessionRequest
+            {
+                HostAddress = $"{address.Host}:{address.Port}",
+                TimeoutMs = (int)Math.Max(1, timeout.TotalMilliseconds),
+                CncSeries = (int)_series,
+            },
+            FocasMessageKind.OpenSessionResponse,
+            cancellationToken).ConfigureAwait(false);
+
+        if (!resp.Success)
+            throw new InvalidOperationException(
+                $"FOCAS Host rejected OpenSession for {address}: {resp.ErrorCode ?? "?"} — {resp.Error}");
+
+        _sessionId = resp.SessionId;
+        _connected = true;
+    }
+
+    public async Task<(object? value, uint status)> ReadAsync(
+        FocasAddress address, FocasDataType type, CancellationToken cancellationToken)
+    {
+        if (!_connected) return (null, FocasStatusMapper.BadCommunicationError);
+
+        var resp = await _ipc.CallAsync<ReadRequest, ReadResponse>(
+            FocasMessageKind.ReadRequest,
+            new ReadRequest
+            {
+                SessionId = _sessionId,
+                Address = ToDto(address),
+                DataType = (int)type,
+            },
+            FocasMessageKind.ReadResponse,
+            cancellationToken).ConfigureAwait(false);
+
+        if (!resp.Success) return (null, resp.StatusCode);
+
+        var value = DecodeValue(resp.ValueBytes, resp.ValueTypeCode);
+        return (value, resp.StatusCode);
+    }
+
+    public async Task<uint> WriteAsync(
+        FocasAddress address, FocasDataType type, object? value, CancellationToken cancellationToken)
+    {
+        if (!_connected) return FocasStatusMapper.BadCommunicationError;
+
+        // PMC bit writes get the first-class RMW frame so the critical section stays on the Host.
+        if (address.Kind == FocasAreaKind.Pmc && type == FocasDataType.Bit && address.BitIndex is int bit)
+        {
+            var bitResp = await _ipc.CallAsync<PmcBitWriteRequest, PmcBitWriteResponse>(
+                FocasMessageKind.PmcBitWriteRequest,
+                new PmcBitWriteRequest
+                {
+                    SessionId = _sessionId,
+                    Address = ToDto(address),
+                    BitIndex = bit,
+                    Value = Convert.ToBoolean(value),
+                },
+                FocasMessageKind.PmcBitWriteResponse,
+                cancellationToken).ConfigureAwait(false);
+            return bitResp.StatusCode;
+        }
+
+        var resp = await _ipc.CallAsync<WriteRequest, WriteResponse>(
+            FocasMessageKind.WriteRequest,
+            new WriteRequest
+            {
+                SessionId = _sessionId,
+                Address = ToDto(address),
+                DataType = (int)type,
+                ValueTypeCode = (int)type,
+                ValueBytes = EncodeValue(value, type),
+            },
+            FocasMessageKind.WriteResponse,
+            cancellationToken).ConfigureAwait(false);
+
+        return resp.StatusCode;
+    }
+
+    public async Task<bool> ProbeAsync(CancellationToken cancellationToken)
+    {
+        if (!_connected) return false;
+        try
+        {
+            var resp = await _ipc.CallAsync<ProbeRequest, ProbeResponse>(
+                FocasMessageKind.ProbeRequest,
+                new ProbeRequest { SessionId = _sessionId },
+                FocasMessageKind.ProbeResponse,
+                cancellationToken).ConfigureAwait(false);
+            return resp.Healthy;
+        }
+        catch { return false; }
+    }
+
+    public void Dispose()
+    {
+        if (_connected)
+        {
+            try
+            {
+                _ipc.SendOneWayAsync(FocasMessageKind.CloseSessionRequest,
+                    new CloseSessionRequest { SessionId = _sessionId }, CancellationToken.None)
+                    .GetAwaiter().GetResult();
+            }
+            catch { /* best effort */ }
+            _connected = false;
+        }
+        _ipc.DisposeAsync().AsTask().GetAwaiter().GetResult();
+    }
+
+    private static FocasAddressDto ToDto(FocasAddress addr) => new()
+    {
+        Kind = (int)addr.Kind,
+        PmcLetter = addr.PmcLetter,
+        Number = addr.Number,
+        BitIndex = addr.BitIndex,
+    };
+
+    private static byte[]? EncodeValue(object? value, FocasDataType type)
+    {
+        if (value is null) return null;
+        return type switch
+        {
+            FocasDataType.Bit     => MessagePackSerializer.Serialize(Convert.ToBoolean(value)),
+            FocasDataType.Byte    => MessagePackSerializer.Serialize(Convert.ToByte(value)),
+            FocasDataType.Int16   => MessagePackSerializer.Serialize(Convert.ToInt16(value)),
+            FocasDataType.Int32   => MessagePackSerializer.Serialize(Convert.ToInt32(value)),
+            FocasDataType.Float32 => MessagePackSerializer.Serialize(Convert.ToSingle(value)),
+            FocasDataType.Float64 => MessagePackSerializer.Serialize(Convert.ToDouble(value)),
+            FocasDataType.String  => MessagePackSerializer.Serialize(Convert.ToString(value) ?? string.Empty),
+            _ => MessagePackSerializer.Serialize(Convert.ToInt32(value)),
+        };
+    }
+
+    private static object? DecodeValue(byte[]? bytes, int typeCode)
+    {
+        if (bytes is null) return null;
+        return typeCode switch
+        {
+            FocasDataTypeCode.Bit     => MessagePackSerializer.Deserialize<bool>(bytes),
+            FocasDataTypeCode.Byte    => MessagePackSerializer.Deserialize<byte>(bytes),
+            FocasDataTypeCode.Int16   => MessagePackSerializer.Deserialize<short>(bytes),
+            FocasDataTypeCode.Int32   => MessagePackSerializer.Deserialize<int>(bytes),
+            FocasDataTypeCode.Float32 => MessagePackSerializer.Deserialize<float>(bytes),
+            FocasDataTypeCode.Float64 => MessagePackSerializer.Deserialize<double>(bytes),
+            FocasDataTypeCode.String  => MessagePackSerializer.Deserialize<string>(bytes),
+            _ => MessagePackSerializer.Deserialize<int>(bytes),
+        };
+    }
+}
+
+/// <summary>
+///     Factory producing <see cref="IpcFocasClient"/>s. One pipe connection per
+///     <c>IFocasClient</c> — matches the driver's one-client-per-device invariant. The
+///     deployment wires this into the DI container in place of
+///     <see cref="UnimplementedFocasClientFactory"/>.
+/// </summary>
+public sealed class IpcFocasClientFactory(Func<FocasIpcClient> ipcClientFactory, FocasCncSeries series = FocasCncSeries.Unknown)
+    : IFocasClientFactory
+{
+    public IFocasClient Create() => new IpcFocasClient(ipcClientFactory(), series);
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj

@@ -14,6 +14,7 @@
 
     <ItemGroup>
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.csproj"/>
     </ItemGroup>
 
     <!--

src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -84,7 +84,7 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
         _health = new DriverHealth(DriverState.Initializing, null, null);
         try
         {
-            var plc = new Plc(_options.CpuType, _options.Host, _options.Rack, _options.Slot);
+            var plc = new Plc(_options.CpuType, _options.Host, _options.Port, _options.Rack, _options.Slot);
             // S7netplus writes timeouts into the underlying TcpClient via Plc.WriteTimeout /
             // Plc.ReadTimeout (milliseconds). Set before OpenAsync so the handshake itself
             // honours the bound.

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverEquipmentContentRegistry.cs

@@ -0,0 +1,47 @@
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.OpcUa;
+
+/// <summary>
+///     Holds pre-loaded <see cref="EquipmentNamespaceContent"/> snapshots keyed by
+///     <c>DriverInstanceId</c>. Populated once during <see cref="OpcUaServerService"/> startup
+///     (after <see cref="NodeBootstrap"/> resolves the generation) so the synchronous lookup
+///     delegate on <see cref="OpcUaApplicationHost"/> can serve the walker from memory without
+///     blocking on async DB I/O mid-dispatch.
+/// </summary>
+/// <remarks>
+///     <para>The registry is intentionally a shared mutable singleton with set-once-per-bootstrap
+///     semantics rather than an immutable map passed by value — the composition in Program.cs
+///     builds <see cref="OpcUaApplicationHost"/> before <see cref="NodeBootstrap"/> runs, so the
+///     registry must exist at DI-compose time but be empty until the generation is known. A
+///     driver registered after the initial populate pass simply returns null from
+///     <see cref="Get"/> + the wire-in falls back to the "no UNS content, let DiscoverAsync own
+///     it" path that PR #155 established.</para>
+/// </remarks>
+public sealed class DriverEquipmentContentRegistry
+{
+    private readonly Dictionary<string, EquipmentNamespaceContent> _content =
+        new(StringComparer.OrdinalIgnoreCase);
+    private readonly Lock _lock = new();
+
+    public EquipmentNamespaceContent? Get(string driverInstanceId)
+    {
+        lock (_lock)
+        {
+            return _content.TryGetValue(driverInstanceId, out var c) ? c : null;
+        }
+    }
+
+    public void Set(string driverInstanceId, EquipmentNamespaceContent content)
+    {
+        lock (_lock)
+        {
+            _content[driverInstanceId] = content;
+        }
+    }
+
+    public int Count
+    {
+        get { lock (_lock) { return _content.Count; } }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/EquipmentNamespaceContentLoader.cs

@@ -0,0 +1,86 @@
+using Microsoft.EntityFrameworkCore;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.OpcUa;
+
+/// <summary>
+///     Loads the <see cref="EquipmentNamespaceContent"/> snapshot the
+///     <see cref="EquipmentNodeWalker"/> consumes, scoped to a single
+///     (driverInstanceId, generationId) pair. Joins the four row sets the walker expects:
+///     UnsAreas for the driver's cluster, UnsLines under those areas, Equipment bound to
+///     this driver + its lines, and Tags bound to this driver + its equipment — all at the
+///     supplied generation.
+/// </summary>
+/// <remarks>
+///     <para>The walker is driver-instance-scoped (decisions #116–#121 put the UNS in the
+///     Equipment-kind namespace owned by one driver instance at a time), so this loader is
+///     too — a single call returns one driver's worth of rows, never the whole fleet.</para>
+///
+///     <para>Returns <c>null</c> when the driver instance has no Equipment rows at the
+///     supplied generation. The wire-in in <see cref="OpcUaApplicationHost"/> treats null as
+///     "this driver has no UNS content, skip the walker and let DiscoverAsync own the whole
+///     address space" — the backward-compat path for drivers whose namespace kind is not
+///     Equipment (Modbus / AB CIP / TwinCAT / FOCAS).</para>
+/// </remarks>
+public sealed class EquipmentNamespaceContentLoader
+{
+    private readonly OtOpcUaConfigDbContext _db;
+
+    public EquipmentNamespaceContentLoader(OtOpcUaConfigDbContext db)
+    {
+        _db = db;
+    }
+
+    /// <summary>
+    ///     Load the walker-shaped snapshot for <paramref name="driverInstanceId"/> at
+    ///     <paramref name="generationId"/>. Returns <c>null</c> when the driver has no
+    ///     Equipment rows at that generation.
+    /// </summary>
+    public async Task<EquipmentNamespaceContent?> LoadAsync(
+        string driverInstanceId, long generationId, CancellationToken ct)
+    {
+        var equipment = await _db.Equipment
+            .AsNoTracking()
+            .Where(e => e.DriverInstanceId == driverInstanceId && e.GenerationId == generationId && e.Enabled)
+            .ToListAsync(ct).ConfigureAwait(false);
+
+        if (equipment.Count == 0)
+            return null;
+
+        // Filter UNS tree to only the lines + areas that host at least one Equipment bound to
+        // this driver — skips loading unrelated UNS branches from the cluster. LinesByArea
+        // grouping is driven off the Equipment rows so an empty line (no equipment) doesn't
+        // pull a pointless folder into the walker output.
+        var lineIds = equipment.Select(e => e.UnsLineId).Distinct(StringComparer.OrdinalIgnoreCase).ToArray();
+
+        var lines = await _db.UnsLines
+            .AsNoTracking()
+            .Where(l => l.GenerationId == generationId && lineIds.Contains(l.UnsLineId))
+            .ToListAsync(ct).ConfigureAwait(false);
+
+        var areaIds = lines.Select(l => l.UnsAreaId).Distinct(StringComparer.OrdinalIgnoreCase).ToArray();
+
+        var areas = await _db.UnsAreas
+            .AsNoTracking()
+            .Where(a => a.GenerationId == generationId && areaIds.Contains(a.UnsAreaId))
+            .ToListAsync(ct).ConfigureAwait(false);
+
+        // Tags belonging to this driver at this generation. Walker skips Tags with null
+        // EquipmentId (those are SystemPlatform-kind Galaxy tags per decision #120) but we
+        // load them anyway so the same rowset can drive future non-Equipment-kind walks
+        // without re-hitting the DB. Filtering here is a future optimization; today the
+        // per-tag cost is bounded by driver scope.
+        var tags = await _db.Tags
+            .AsNoTracking()
+            .Where(t => t.DriverInstanceId == driverInstanceId && t.GenerationId == generationId)
+            .ToListAsync(ct).ConfigureAwait(false);
+
+        return new EquipmentNamespaceContent(
+            Areas: areas,
+            Lines: lines,
+            Equipment: equipment,
+            Tags: tags);
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/OpcUaApplicationHost.cs

@@ -29,6 +29,7 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
     private readonly StaleConfigFlag? _staleConfigFlag;
     private readonly Func<string, ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverTier>? _tierLookup;
     private readonly Func<string, string?>? _resilienceConfigLookup;
+    private readonly Func<string, ZB.MOM.WW.OtOpcUa.Core.OpcUa.EquipmentNamespaceContent?>? _equipmentContentLookup;
     private readonly ILoggerFactory _loggerFactory;
     private readonly ILogger<OpcUaApplicationHost> _logger;
     private ApplicationInstance? _application;
@@ -43,7 +44,8 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
         NodeScopeResolver? scopeResolver = null,
         StaleConfigFlag? staleConfigFlag = null,
         Func<string, ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverTier>? tierLookup = null,
-        Func<string, string?>? resilienceConfigLookup = null)
+        Func<string, string?>? resilienceConfigLookup = null,
+        Func<string, ZB.MOM.WW.OtOpcUa.Core.OpcUa.EquipmentNamespaceContent?>? equipmentContentLookup = null)
     {
         _options = options;
         _driverHost = driverHost;
@@ -54,6 +56,7 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
         _staleConfigFlag = staleConfigFlag;
         _tierLookup = tierLookup;
         _resilienceConfigLookup = resilienceConfigLookup;
+        _equipmentContentLookup = equipmentContentLookup;
         _loggerFactory = loggerFactory;
         _logger = logger;
     }
@@ -103,11 +106,31 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
         // Drive each driver's discovery through its node manager. The node manager IS the
         // IAddressSpaceBuilder; GenericDriverNodeManager captures alarm-condition sinks into
         // its internal map and wires OnAlarmEvent → sink routing.
+        //
+        // ADR-001 Option A — when an EquipmentNamespaceContent is supplied for an
+        // Equipment-kind driver, run the EquipmentNodeWalker BEFORE the driver's DiscoverAsync
+        // so the UNS folder skeleton (Area/Line/Equipment) + Identification sub-folders +
+        // the five identifier properties (decision #121) are in place. DiscoverAsync then
+        // streams the driver's native shape on top; Tag rows bound to Equipment already
+        // materialized via the walker don't get duplicated because the driver's DiscoverAsync
+        // output is authoritative for its own native references only.
         foreach (var nodeManager in _server.DriverNodeManagers)
         {
             var driverId = nodeManager.Driver.DriverInstanceId;
             try
             {
+                if (_equipmentContentLookup is not null)
+                {
+                    var content = _equipmentContentLookup(driverId);
+                    if (content is not null)
+                    {
+                        ZB.MOM.WW.OtOpcUa.Core.OpcUa.EquipmentNodeWalker.Walk(nodeManager, content);
+                        _logger.LogInformation(
+                            "UNS walker populated {Areas} area(s), {Lines} line(s), {Equipment} equipment, {Tags} tag(s) for driver {Driver}",
+                            content.Areas.Count, content.Lines.Count, content.Equipment.Count, content.Tags.Count, driverId);
+                    }
+                }
+
                 var generic = new GenericDriverNodeManager(nodeManager.Driver);
                 await generic.BuildAddressSpaceAsync(nodeManager, ct).ConfigureAwait(false);
                 _logger.LogInformation("Address space populated for driver {Driver}", driverId);

src/ZB.MOM.WW.OtOpcUa.Server/OpcUaServerService.cs

@@ -1,3 +1,4 @@
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using ZB.MOM.WW.OtOpcUa.Core.Hosting;
@@ -15,6 +16,8 @@ public sealed class OpcUaServerService(
     NodeBootstrap bootstrap,
     DriverHost driverHost,
     OpcUaApplicationHost applicationHost,
+    DriverEquipmentContentRegistry equipmentContentRegistry,
+    IServiceScopeFactory scopeFactory,
     ILogger<OpcUaServerService> logger) : BackgroundService
 {
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
@@ -24,6 +27,15 @@ public sealed class OpcUaServerService(
         var result = await bootstrap.LoadCurrentGenerationAsync(stoppingToken);
         logger.LogInformation("Bootstrap complete: source={Source} generation={Gen}", result.Source, result.GenerationId);
 
+        // ADR-001 Option A — populate per-driver Equipment namespace snapshots into the
+        // registry before StartAsync walks the address space. The walker on the OPC UA side
+        // reads synchronously from the registry; pre-loading here means the hot path stays
+        // non-blocking + each driver pays at most one Config-DB query at bootstrap time.
+        // Skipped when no generation is Published yet — the fleet boots into a UNS-less
+        // address space until the first publish, then the registry fills on next restart.
+        if (result.GenerationId is { } gen)
+            await PopulateEquipmentContentAsync(gen, stoppingToken);
+
         // PR 17: stand up the OPC UA server + drive discovery per registered driver. Driver
         // registration itself (RegisterAsync on DriverHost) happens during an earlier DI
         // extension once the central config DB query + per-driver factory land; for now the
@@ -48,4 +60,30 @@ public sealed class OpcUaServerService(
         await applicationHost.DisposeAsync();
         await driverHost.DisposeAsync();
     }
+
+    /// <summary>
+    ///     Pre-load an <c>EquipmentNamespaceContent</c> snapshot for each registered driver at
+    ///     the bootstrapped generation. Null results (driver has no Equipment rows —
+    ///     Modbus/AB CIP/TwinCAT/FOCAS today per decisions #116–#121) are skipped: the walker
+    ///     wire-in sees Get(driverId) return null + falls back to DiscoverAsync-owns-it.
+    ///     Opens one scope so the scoped <c>OtOpcUaConfigDbContext</c> is shared across all
+    ///     per-driver queries rather than paying scope-setup overhead per driver.
+    /// </summary>
+    private async Task PopulateEquipmentContentAsync(long generationId, CancellationToken ct)
+    {
+        using var scope = scopeFactory.CreateScope();
+        var loader = scope.ServiceProvider.GetRequiredService<EquipmentNamespaceContentLoader>();
+
+        var loaded = 0;
+        foreach (var driverId in driverHost.RegisteredDriverIds)
+        {
+            var content = await loader.LoadAsync(driverId, generationId, ct).ConfigureAwait(false);
+            if (content is null) continue;
+            equipmentContentRegistry.Set(driverId, content);
+            loaded++;
+        }
+        logger.LogInformation(
+            "Equipment namespace snapshots loaded for {Count}/{Total} driver(s) at generation {Gen}",
+            loaded, driverHost.RegisteredDriverIds.Count, generationId);
+    }
 }

src/ZB.MOM.WW.OtOpcUa.Server/Program.cs

@@ -86,7 +86,25 @@ builder.Services.AddSingleton<IUserAuthenticator>(sp => ldapOptions.Enabled
 builder.Services.AddSingleton<ILocalConfigCache>(_ => new LiteDbConfigCache(options.LocalCachePath));
 builder.Services.AddSingleton<DriverHost>();
 builder.Services.AddSingleton<NodeBootstrap>();
-builder.Services.AddSingleton<OpcUaApplicationHost>();
+
+// ADR-001 Option A wiring — the registry is the handoff between OpcUaServerService's
+// bootstrap-time population pass + OpcUaApplicationHost's StartAsync walker invocation.
+// DriverEquipmentContentRegistry.Get is the equipmentContentLookup delegate that PR #155
+// added to OpcUaApplicationHost's ctor seam.
+builder.Services.AddSingleton<DriverEquipmentContentRegistry>();
+builder.Services.AddScoped<EquipmentNamespaceContentLoader>();
+
+builder.Services.AddSingleton<OpcUaApplicationHost>(sp =>
+{
+    var registry = sp.GetRequiredService<DriverEquipmentContentRegistry>();
+    return new OpcUaApplicationHost(
+        sp.GetRequiredService<OpcUaServerOptions>(),
+        sp.GetRequiredService<DriverHost>(),
+        sp.GetRequiredService<IUserAuthenticator>(),
+        sp.GetRequiredService<ILoggerFactory>(),
+        sp.GetRequiredService<ILogger<OpcUaApplicationHost>>(),
+        equipmentContentLookup: registry.Get);
+});
 builder.Services.AddHostedService<OpcUaServerService>();
 
 // Central-config DB access for the host-status publisher (LMX follow-up #7). Scoped context

src/ZB.MOM.WW.OtOpcUa.Server/Security/NodeScopeResolver.cs

@@ -1,42 +1,83 @@
+using System.Collections.Frozen;
 using ZB.MOM.WW.OtOpcUa.Core.Authorization;
 
 namespace ZB.MOM.WW.OtOpcUa.Server.Security;
 
 /// <summary>
 ///     Maps a driver-side full reference (e.g. <c>"TestMachine_001/Oven/SetPoint"</c>) to the
-///     <see cref="NodeScope"/> the Phase 6.2 evaluator walks. Today a simplified resolver that
-///     returns a cluster-scoped + tag-only scope — the deeper UnsArea / UnsLine / Equipment
-///     path lookup from the live Configuration DB is a Stream C.12 follow-up.
+///     <see cref="NodeScope"/> the Phase 6.2 evaluator walks. Supports two modes:
+///     <list type="bullet">
+///     <item>
+///         <b>Cluster-only (pre-ADR-001)</b> — when no path index is supplied the resolver
+///         returns a flat <c>ClusterId + TagId</c> scope. Sufficient while the
+///         Config-DB-driven Equipment walker isn't live; Cluster-level grants cascade to every
+///         tag below per decision #129, so finer per-Equipment grants are effectively
+///         cluster-wide at dispatch.
+///     </item>
+///     <item>
+///         <b>Full-path (post-ADR-001 Task B)</b> — when an index is supplied, the resolver
+///         joins the full reference against the index to produce a complete
+///         <c>Cluster → Namespace → UnsArea → UnsLine → Equipment → Tag</c> scope. Unblocks
+///         per-Equipment / per-UnsLine ACL grants at the dispatch layer.
+///     </item>
+///     </list>
 /// </summary>
 /// <remarks>
-///     <para>The flat cluster-level scope is sufficient for v2 GA because Phase 6.2 ACL grants
-///     at the Cluster scope cascade to every tag below (decision #129 — additive grants). The
-///     finer hierarchy only matters when operators want per-area or per-equipment grants;
-///     those still work for Cluster-level grants, and landing the finer resolution in a
-///     follow-up doesn't regress the base security model.</para>
+///     <para>The index is pre-loaded by the Server bootstrap against the published generation;
+///     the resolver itself does no live DB access. Resolve is O(1) dictionary lookup on the
+///     hot path; the fallback for unknown fullReference strings produces the same cluster-only
+///     scope the pre-ADR-001 resolver returned — new tags picked up via driver discovery but
+///     not yet indexed (e.g. between a DiscoverAsync result and the next generation publish)
+///     stay addressable without a scope-resolver crash.</para>
 ///
-///     <para>Thread-safety: the resolver is stateless once constructed. Callers may cache a
-///     single instance per DriverNodeManager without locks.</para>
+///     <para>Thread-safety: both constructor paths freeze inputs into immutable state. Callers
+///     may cache a single instance per DriverNodeManager without locks. Swap atomically on
+///     generation change via the server's publish pipeline.</para>
 /// </remarks>
 public sealed class NodeScopeResolver
 {
     private readonly string _clusterId;
+    private readonly FrozenDictionary<string, NodeScope>? _index;
 
+    /// <summary>Cluster-only resolver — pre-ADR-001 behavior. Kept for Server processes that
+    /// haven't wired the Config-DB snapshot flow yet.</summary>
     public NodeScopeResolver(string clusterId)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(clusterId);
         _clusterId = clusterId;
+        _index = null;
+    }
+
+    /// <summary>
+    ///     Full-path resolver (ADR-001 Task B). <paramref name="pathIndex"/> maps each known
+    ///     driver-side full reference to its pre-resolved <see cref="NodeScope"/> carrying
+    ///     every UNS level populated. Entries are typically produced by joining
+    ///     <c>Tag → Equipment → UnsLine → UnsArea</c> rows of the published generation against
+    ///     the driver's discovered full references (or against <c>Tag.TagConfig</c> directly
+    ///     when the walker is config-primary per ADR-001 Option A).
+    /// </summary>
+    public NodeScopeResolver(string clusterId, IReadOnlyDictionary<string, NodeScope> pathIndex)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(clusterId);
+        ArgumentNullException.ThrowIfNull(pathIndex);
+        _clusterId = clusterId;
+        _index = pathIndex.ToFrozenDictionary(StringComparer.Ordinal);
     }
 
     /// <summary>
     ///     Resolve a node scope for the given driver-side <paramref name="fullReference"/>.
-    ///     Phase 1 shape: returns <c>ClusterId</c> + <c>TagId = fullReference</c> only;
-    ///     NamespaceId / UnsArea / UnsLine / Equipment stay null. A future resolver will
-    ///     join against the Configuration DB to populate the full path.
+    ///     Returns the indexed full-path scope when available; falls back to cluster-only
+    ///     (TagId populated only) when the index is absent or the reference isn't indexed.
+    ///     The fallback is the same shape the pre-ADR-001 resolver produced, so the authz
+    ///     evaluator behaves identically for un-indexed references.
     /// </summary>
     public NodeScope Resolve(string fullReference)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(fullReference);
+
+        if (_index is not null && _index.TryGetValue(fullReference, out var indexed))
+            return indexed;
+
         return new NodeScope
         {
             ClusterId = _clusterId,

src/ZB.MOM.WW.OtOpcUa.Server/Security/ScopePathIndexBuilder.cs

@@ -0,0 +1,81 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Security;
+
+/// <summary>
+///     Builds the <see cref="NodeScope"/> path index consumed by <see cref="NodeScopeResolver"/>
+///     from a Config-DB snapshot of a single published generation. Runs once per generation
+///     (or on every generation change) at the Server bootstrap layer; the produced index is
+///     immutable + hot-path readable per ADR-001 Task B.
+/// </summary>
+/// <remarks>
+///     <para>The index key is the driver-side full reference (<c>Tag.TagConfig</c>) — the same
+///     string the dispatch layer passes to <see cref="NodeScopeResolver.Resolve"/>. The value
+///     is a <see cref="NodeScope"/> with every UNS level populated:
+///     <c>ClusterId / NamespaceId / UnsAreaId / UnsLineId / EquipmentId / TagId</c>. Tag rows
+///     with null <c>EquipmentId</c> (SystemPlatform-namespace Galaxy tags per decision #120)
+///     are excluded from the index — the cluster-only fallback path in the resolver handles
+///     them without needing an index entry.</para>
+///
+///     <para>Duplicate keys are not expected but would be indicative of corrupt data — the
+///     builder throws <see cref="InvalidOperationException"/> on collision so a config drift
+///     surfaces at bootstrap instead of producing silently-last-wins scopes at dispatch.</para>
+/// </remarks>
+public static class ScopePathIndexBuilder
+{
+    /// <summary>
+    ///     Build a fullReference → NodeScope index from the four Config-DB collections for a
+    ///     single namespace. Callers must filter inputs to a single
+    ///     <see cref="Namespace"/> + the same <see cref="ConfigGeneration"/> upstream.
+    /// </summary>
+    /// <param name="clusterId">Owning cluster — populates <see cref="NodeScope.ClusterId"/>.</param>
+    /// <param name="namespaceId">Owning namespace — populates <see cref="NodeScope.NamespaceId"/>.</param>
+    /// <param name="content">Pre-loaded rows for the namespace.</param>
+    public static IReadOnlyDictionary<string, NodeScope> Build(
+        string clusterId,
+        string namespaceId,
+        EquipmentNamespaceContent content)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(clusterId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(namespaceId);
+        ArgumentNullException.ThrowIfNull(content);
+
+        var areaByLine = content.Lines.ToDictionary(l => l.UnsLineId, l => l.UnsAreaId, StringComparer.OrdinalIgnoreCase);
+        var lineByEquipment = content.Equipment.ToDictionary(e => e.EquipmentId, e => e.UnsLineId, StringComparer.OrdinalIgnoreCase);
+
+        var index = new Dictionary<string, NodeScope>(StringComparer.Ordinal);
+
+        foreach (var tag in content.Tags)
+        {
+            // Null EquipmentId = SystemPlatform-namespace tag per decision #110 — skip; the
+            // cluster-only resolver fallback handles those without needing an index entry.
+            if (string.IsNullOrEmpty(tag.EquipmentId)) continue;
+
+            // Broken FK — Tag references a missing Equipment row. Skip rather than crash;
+            // sp_ValidateDraft should have caught this at publish, so any drift here is
+            // unexpected but non-fatal.
+            if (!lineByEquipment.TryGetValue(tag.EquipmentId, out var lineId)) continue;
+            if (!areaByLine.TryGetValue(lineId, out var areaId)) continue;
+
+            var scope = new NodeScope
+            {
+                ClusterId = clusterId,
+                NamespaceId = namespaceId,
+                UnsAreaId = areaId,
+                UnsLineId = lineId,
+                EquipmentId = tag.EquipmentId,
+                TagId = tag.TagConfig,
+                Kind = NodeHierarchyKind.Equipment,
+            };
+
+            if (!index.TryAdd(tag.TagConfig, scope))
+                throw new InvalidOperationException(
+                    $"Duplicate fullReference '{tag.TagConfig}' in Equipment namespace '{namespaceId}'. " +
+                    "Config data is corrupt — two Tag rows produced the same wire-level address.");
+        }
+
+        return index;
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/OpcUa/EquipmentNodeWalkerTests.cs

@@ -0,0 +1,221 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.OpcUa;
+
+[Trait("Category", "Unit")]
+public sealed class EquipmentNodeWalkerTests
+{
+    [Fact]
+    public void Walk_EmptyContent_EmitsNothing()
+    {
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, new EquipmentNamespaceContent([], [], [], []));
+
+        rec.Children.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Walk_EmitsArea_Line_Equipment_Folders_In_UnsOrder()
+    {
+        var content = new EquipmentNamespaceContent(
+            Areas: [Area("area-1", "warsaw"), Area("area-2", "berlin")],
+            Lines: [Line("line-1", "area-1", "oven-line"), Line("line-2", "area-2", "press-line")],
+            Equipment: [Eq("eq-1", "line-1", "oven-3"), Eq("eq-2", "line-2", "press-7")],
+            Tags: []);
+
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, content);
+
+        rec.Children.Select(c => c.BrowseName).ShouldBe(["berlin", "warsaw"]);   // ordered by Name
+        var warsaw = rec.Children.First(c => c.BrowseName == "warsaw");
+        warsaw.Children.Select(c => c.BrowseName).ShouldBe(["oven-line"]);
+        warsaw.Children[0].Children.Select(c => c.BrowseName).ShouldBe(["oven-3"]);
+    }
+
+    [Fact]
+    public void Walk_AddsFiveIdentifierProperties_OnEquipmentNode_Skipping_NullZTagSapid()
+    {
+        var uuid = Guid.NewGuid();
+        var eq = Eq("eq-1", "line-1", "oven-3");
+        eq.EquipmentUuid = uuid;
+        eq.MachineCode = "MC-42";
+        eq.ZTag = null;
+        eq.SAPID = null;
+        var content = new EquipmentNamespaceContent(
+            [Area("area-1", "warsaw")], [Line("line-1", "area-1", "line-a")], [eq], []);
+
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, content);
+
+        var equipmentNode = rec.Children[0].Children[0].Children[0];
+        var props = equipmentNode.Properties.Select(p => p.BrowseName).ToList();
+        props.ShouldContain("EquipmentId");
+        props.ShouldContain("EquipmentUuid");
+        props.ShouldContain("MachineCode");
+        props.ShouldNotContain("ZTag");
+        props.ShouldNotContain("SAPID");
+        equipmentNode.Properties.First(p => p.BrowseName == "EquipmentUuid").Value.ShouldBe(uuid.ToString());
+    }
+
+    [Fact]
+    public void Walk_Adds_ZTag_And_SAPID_When_Present()
+    {
+        var eq = Eq("eq-1", "line-1", "oven-3");
+        eq.ZTag = "ZT-0042";
+        eq.SAPID = "10000042";
+        var content = new EquipmentNamespaceContent(
+            [Area("area-1", "warsaw")], [Line("line-1", "area-1", "line-a")], [eq], []);
+
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, content);
+
+        var equipmentNode = rec.Children[0].Children[0].Children[0];
+        equipmentNode.Properties.First(p => p.BrowseName == "ZTag").Value.ShouldBe("ZT-0042");
+        equipmentNode.Properties.First(p => p.BrowseName == "SAPID").Value.ShouldBe("10000042");
+    }
+
+    [Fact]
+    public void Walk_Materializes_Identification_Subfolder_When_AnyFieldPresent()
+    {
+        var eq = Eq("eq-1", "line-1", "oven-3");
+        eq.Manufacturer = "Trumpf";
+        eq.Model = "TruLaser-3030";
+        var content = new EquipmentNamespaceContent(
+            [Area("area-1", "warsaw")], [Line("line-1", "area-1", "line-a")], [eq], []);
+
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, content);
+
+        var equipmentNode = rec.Children[0].Children[0].Children[0];
+        var identification = equipmentNode.Children.FirstOrDefault(c => c.BrowseName == "Identification");
+        identification.ShouldNotBeNull();
+        identification!.Properties.Select(p => p.BrowseName).ShouldContain("Manufacturer");
+        identification.Properties.Select(p => p.BrowseName).ShouldContain("Model");
+    }
+
+    [Fact]
+    public void Walk_Omits_Identification_Subfolder_When_AllFieldsNull()
+    {
+        var eq = Eq("eq-1", "line-1", "oven-3");  // no identification fields
+        var content = new EquipmentNamespaceContent(
+            [Area("area-1", "warsaw")], [Line("line-1", "area-1", "line-a")], [eq], []);
+
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, content);
+
+        var equipmentNode = rec.Children[0].Children[0].Children[0];
+        equipmentNode.Children.ShouldNotContain(c => c.BrowseName == "Identification");
+    }
+
+    [Fact]
+    public void Walk_Emits_Variable_Per_BoundTag_Under_Equipment()
+    {
+        var eq = Eq("eq-1", "line-1", "oven-3");
+        var tag1 = NewTag("tag-1", "Temperature", "Int32", "plcaddr-01", equipmentId: "eq-1");
+        var tag2 = NewTag("tag-2", "Setpoint", "Float32", "plcaddr-02", equipmentId: "eq-1");
+        var unboundTag = NewTag("tag-3", "Orphan", "Int32", "plcaddr-03", equipmentId: null); // SystemPlatform-style, walker skips
+        var content = new EquipmentNamespaceContent(
+            [Area("area-1", "warsaw")], [Line("line-1", "area-1", "line-a")],
+            [eq], [tag1, tag2, unboundTag]);
+
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, content);
+
+        var equipmentNode = rec.Children[0].Children[0].Children[0];
+        equipmentNode.Variables.Count.ShouldBe(2);
+        equipmentNode.Variables.Select(v => v.BrowseName).ShouldBe(["Setpoint", "Temperature"]);
+        equipmentNode.Variables.First(v => v.BrowseName == "Temperature").AttributeInfo.FullName.ShouldBe("plcaddr-01");
+        equipmentNode.Variables.First(v => v.BrowseName == "Setpoint").AttributeInfo.DriverDataType.ShouldBe(DriverDataType.Float32);
+    }
+
+    [Fact]
+    public void Walk_FallsBack_To_String_For_Unparseable_DataType()
+    {
+        var eq = Eq("eq-1", "line-1", "oven-3");
+        var tag = NewTag("tag-1", "Mystery", "NotARealType", "plcaddr-42", equipmentId: "eq-1");
+        var content = new EquipmentNamespaceContent(
+            [Area("area-1", "warsaw")], [Line("line-1", "area-1", "line-a")], [eq], [tag]);
+
+        var rec = new RecordingBuilder("root");
+        EquipmentNodeWalker.Walk(rec, content);
+
+        var variable = rec.Children[0].Children[0].Children[0].Variables.Single();
+        variable.AttributeInfo.DriverDataType.ShouldBe(DriverDataType.String);
+    }
+
+    // ----- builders for test seed rows -----
+
+    private static UnsArea Area(string id, string name) => new()
+    {
+        UnsAreaId = id, ClusterId = "c1", Name = name, GenerationId = 1,
+    };
+
+    private static UnsLine Line(string id, string areaId, string name) => new()
+    {
+        UnsLineId = id, UnsAreaId = areaId, Name = name, GenerationId = 1,
+    };
+
+    private static Equipment Eq(string equipmentId, string lineId, string name) => new()
+    {
+        EquipmentRowId = Guid.NewGuid(),
+        GenerationId = 1,
+        EquipmentId = equipmentId,
+        EquipmentUuid = Guid.NewGuid(),
+        DriverInstanceId = "drv",
+        UnsLineId = lineId,
+        Name = name,
+        MachineCode = "MC-" + name,
+    };
+
+    private static Tag NewTag(string tagId, string name, string dataType, string address, string? equipmentId) => new()
+    {
+        TagRowId = Guid.NewGuid(),
+        GenerationId = 1,
+        TagId = tagId,
+        DriverInstanceId = "drv",
+        EquipmentId = equipmentId,
+        Name = name,
+        DataType = dataType,
+        AccessLevel = ZB.MOM.WW.OtOpcUa.Configuration.Enums.TagAccessLevel.ReadWrite,
+        TagConfig = address,
+    };
+
+    // ----- recording IAddressSpaceBuilder -----
+
+    private sealed class RecordingBuilder(string browseName) : IAddressSpaceBuilder
+    {
+        public string BrowseName { get; } = browseName;
+        public List<RecordingBuilder> Children { get; } = new();
+        public List<RecordingVariable> Variables { get; } = new();
+        public List<RecordingProperty> Properties { get; } = new();
+
+        public IAddressSpaceBuilder Folder(string name, string _)
+        {
+            var child = new RecordingBuilder(name);
+            Children.Add(child);
+            return child;
+        }
+
+        public IVariableHandle Variable(string name, string _, DriverAttributeInfo attr)
+        {
+            var v = new RecordingVariable(name, attr);
+            Variables.Add(v);
+            return v;
+        }
+
+        public void AddProperty(string name, DriverDataType _, object? value) =>
+            Properties.Add(new RecordingProperty(name, value));
+    }
+
+    private sealed record RecordingProperty(string BrowseName, object? Value);
+
+    private sealed record RecordingVariable(string BrowseName, DriverAttributeInfo AttributeInfo) : IVariableHandle
+    {
+        public string FullReference => AttributeInfo.FullName;
+        public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info) => throw new NotSupportedException();
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbServerFixture.cs

@@ -1,139 +1,116 @@
-using System.Diagnostics;
+using System.Net.Sockets;
 using Xunit;
 using Xunit.Sdk;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests;
 
 /// <summary>
-///     Shared fixture that starts libplctag's <c>ab_server</c> simulator in the background for
-///     the duration of an integration test collection. The fixture takes an
-///     <see cref="AbServerProfile"/> (see <see cref="KnownProfiles"/>) so each AB family — ControlLogix,
-///     CompactLogix, Micro800, GuardLogix — starts the simulator with the right <c>--plc</c>
-///     mode + preseed tag set. Binary is expected on PATH; CI resolves that via a job step
-///     that downloads the pinned Windows build from libplctag GitHub Releases before
-///     <c>dotnet test</c> — see <c>docs/v2/test-data-sources.md §2.CI</c> for the exact step.
+///     Reachability probe for the <c>ab_server</c> Docker container (libplctag's CIP
+///     simulator built via <c>Docker/Dockerfile</c>) or any real AB PLC the
+///     <c>AB_SERVER_ENDPOINT</c> env var points at. Parses
+///     <c>AB_SERVER_ENDPOINT</c> (default <c>localhost:44818</c>) + TCP-connects
+///     once at fixture construction. Tests skip via <see cref="AbServerFactAttribute"/>
+///     / <see cref="AbServerTheoryAttribute"/> when the port isn't live, so
+///     <c>dotnet test</c> stays green on a fresh clone without Docker running.
+///     Matches the <see cref="ModbusSimulatorFixture"/> / <c>Snap7ServerFixture</c> /
+///     <c>OpcPlcFixture</c> shape.
 /// </summary>
 /// <remarks>
-///     <para><c>ab_server</c> is a C binary shipped in libplctag's repo (MIT). On developer
-///     workstations it's built once from source and placed on PATH; on CI the workflow file
-///     fetches a version-pinned prebuilt + stages it. Tests skip (via
-///     <see cref="AbServerFactAttribute"/>) when the binary is not on PATH so a fresh clone
-///     without the simulator still gets a green unit-test run.</para>
-///
-///     <para>Per-family profiles live in <see cref="KnownProfiles"/>. When a test wants a
-///     specific family, instantiate the fixture with that profile — either via a
-///     <see cref="IClassFixture{TFixture}"/> derived type or by constructing directly in a
-///     parametric test (the latter is used below for the smoke suite).</para>
+///     Docker is the only supported launch path — no native-binary spawn + no
+///     PATH lookup. Bring the container up before <c>dotnet test</c>:
+///     <c>docker compose -f Docker/docker-compose.yml --profile controllogix up</c>.
 /// </remarks>
 public sealed class AbServerFixture : IAsyncLifetime
 {
-    private Process? _proc;
+    private const string EndpointEnvVar = "AB_SERVER_ENDPOINT";
 
-    /// <summary>The profile the simulator was started with. Same instance the driver-side options should use.</summary>
+    /// <summary>The profile this fixture instance represents. Parallel family smoke tests
+    /// instantiate the fixture with the profile matching their compose-file service.</summary>
     public AbServerProfile Profile { get; }
-    public int Port { get; }
-    public bool IsAvailable { get; private set; }
 
-    public AbServerFixture() : this(KnownProfiles.ControlLogix, AbServerProfile.DefaultPort) { }
+    public string Host { get; } = "127.0.0.1";
+    public int Port { get; } = AbServerProfile.DefaultPort;
 
-    public AbServerFixture(AbServerProfile profile) : this(profile, AbServerProfile.DefaultPort) { }
+    public AbServerFixture() : this(KnownProfiles.ControlLogix) { }
 
-    public AbServerFixture(AbServerProfile profile, int port)
+    public AbServerFixture(AbServerProfile profile)
     {
         Profile = profile ?? throw new ArgumentNullException(nameof(profile));
-        Port = port;
-    }
 
-    public ValueTask InitializeAsync() => InitializeAsync(default);
-    public ValueTask DisposeAsync() => DisposeAsync(default);
-
-    public async ValueTask InitializeAsync(CancellationToken cancellationToken)
-    {
-        if (LocateBinary() is not string binary)
+        // Endpoint override applies to both host + port — targeting a real PLC at
+        // non-default host or port shouldn't need fixture changes.
+        if (Environment.GetEnvironmentVariable(EndpointEnvVar) is { Length: > 0 } raw)
         {
-            IsAvailable = false;
-            return;
+            var parts = raw.Split(':', 2);
+            Host = parts[0];
+            if (parts.Length == 2 && int.TryParse(parts[1], out var p)) Port = p;
         }
-        IsAvailable = true;
-
-        _proc = new Process
-        {
-            StartInfo = new ProcessStartInfo
-            {
-                FileName = binary,
-                Arguments = Profile.BuildCliArgs(Port),
-                RedirectStandardOutput = true,
-                RedirectStandardError = true,
-                UseShellExecute = false,
-                CreateNoWindow = true,
-            },
-        };
-        _proc.Start();
-
-        // Give the server a moment to accept its listen socket before tests try to connect.
-        await Task.Delay(500, cancellationToken).ConfigureAwait(false);
     }
 
-    public ValueTask DisposeAsync(CancellationToken cancellationToken)
+    public ValueTask InitializeAsync() => ValueTask.CompletedTask;
+    public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+
+    /// <summary>
+    ///     <c>true</c> when ab_server is reachable at this fixture's Host/Port. Used by
+    ///     <see cref="AbServerFactAttribute"/> / <see cref="AbServerTheoryAttribute"/>
+    ///     to decide whether to skip tests on a fresh clone without a running container.
+    /// </summary>
+    public static bool IsServerAvailable() =>
+        TcpProbe(ResolveHost(), ResolvePort());
+
+    private static string ResolveHost() =>
+        Environment.GetEnvironmentVariable(EndpointEnvVar)?.Split(':', 2)[0] ?? "127.0.0.1";
+
+    private static int ResolvePort()
+    {
+        var raw = Environment.GetEnvironmentVariable(EndpointEnvVar);
+        if (raw is null) return AbServerProfile.DefaultPort;
+        var parts = raw.Split(':', 2);
+        return parts.Length == 2 && int.TryParse(parts[1], out var p) ? p : AbServerProfile.DefaultPort;
+    }
+
+    /// <summary>One-shot TCP probe; 500 ms budget so a missing container fails the probe fast.</summary>
+    private static bool TcpProbe(string host, int port)
     {
         try
         {
-            if (_proc is { HasExited: false })
-            {
-                _proc.Kill(entireProcessTree: true);
-                _proc.WaitForExit(5_000);
-            }
+            using var client = new TcpClient();
+            var task = client.ConnectAsync(host, port);
+            return task.Wait(TimeSpan.FromMilliseconds(500)) && client.Connected;
         }
-        catch { /* best-effort cleanup */ }
-        _proc?.Dispose();
-        return ValueTask.CompletedTask;
-    }
-
-    /// <summary>
-    ///     Locate <c>ab_server</c> on PATH. Returns <c>null</c> when missing — tests that
-    ///     depend on it should use <see cref="AbServerFactAttribute"/> so CI runs without the binary
-    ///     simply skip rather than fail.
-    /// </summary>
-    public static string? LocateBinary()
-    {
-        var names = new[] { "ab_server.exe", "ab_server" };
-        var path = Environment.GetEnvironmentVariable("PATH") ?? "";
-        foreach (var dir in path.Split(Path.PathSeparator))
-        {
-            foreach (var name in names)
-            {
-                var candidate = Path.Combine(dir, name);
-                if (File.Exists(candidate)) return candidate;
-            }
-        }
-        return null;
+        catch { return false; }
     }
 }
 
 /// <summary>
-///     <c>[Fact]</c>-equivalent that skips when <c>ab_server</c> is not available on PATH.
-///     Integration tests use this instead of <c>[Fact]</c> so a developer box without
-///     <c>ab_server</c> installed still gets a green run.
+///     <c>[Fact]</c>-equivalent that skips when ab_server isn't reachable — accepts a
+///     live Docker listener on <c>localhost:44818</c> or an <c>AB_SERVER_ENDPOINT</c>
+///     override pointing at a real PLC.
 /// </summary>
 public sealed class AbServerFactAttribute : FactAttribute
 {
     public AbServerFactAttribute()
     {
-        if (AbServerFixture.LocateBinary() is null)
-            Skip = "ab_server not on PATH; install libplctag test binaries to run.";
+        if (!AbServerFixture.IsServerAvailable())
+            Skip = "ab_server not reachable. Start the Docker container " +
+                   "(docker compose -f Docker/docker-compose.yml --profile controllogix up) " +
+                   "or set AB_SERVER_ENDPOINT to a real PLC.";
     }
 }
 
 /// <summary>
-///     <c>[Theory]</c>-equivalent that skips when <c>ab_server</c> is not on PATH. Pair with
-///     <c>[MemberData(nameof(KnownProfiles.All))]</c>-style providers to run one theory row per
-///     profile so a single test covers all four families.
+///     <c>[Theory]</c>-equivalent with the same availability rules as
+///     <see cref="AbServerFactAttribute"/>. Pair with
+///     <c>[MemberData(nameof(KnownProfiles.All))]</c>-style providers to run one theory
+///     row per family.
 /// </summary>
 public sealed class AbServerTheoryAttribute : TheoryAttribute
 {
     public AbServerTheoryAttribute()
     {
-        if (AbServerFixture.LocateBinary() is null)
-            Skip = "ab_server not on PATH; install libplctag test binaries to run.";
+        if (!AbServerFixture.IsServerAvailable())
+            Skip = "ab_server not reachable. Start the Docker container " +
+                   "(docker compose -f Docker/docker-compose.yml --profile controllogix up) " +
+                   "or set AB_SERVER_ENDPOINT to a real PLC.";
     }
 }

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbServerProfile.cs

@@ -3,130 +3,51 @@ using ZB.MOM.WW.OtOpcUa.Driver.AbCip;
 namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests;
 
 /// <summary>
-///     Per-family provisioning profile for the <c>ab_server</c> simulator. Instead of hard-coding
-///     one fixture shape + one set of CLI args, each integration test picks a profile matching the
-///     family it wants to exercise — ControlLogix / CompactLogix / Micro800 / GuardLogix. The
-///     profile composes the CLI arg list passed to <c>ab_server</c> + the tag-definition set the
-///     driver uses to address the simulator's pre-provisioned tags.
+///     Per-family marker for the <c>ab_server</c> Docker compose profile a given test
+///     targets. The compose file (<c>Docker/docker-compose.yml</c>) is the canonical
+///     source of truth for which tags a family seeds + which <c>--plc</c> mode the
+///     simulator boots in; this record just ties a family enum to operator-facing
+///     notes so fixture + test code can filter / branch by family.
 /// </summary>
-/// <param name="Family">OtOpcUa driver family this profile targets. Drives
-///     <see cref="AbCipDeviceOptions.PlcFamily"/> + driver-side connection-parameter profile
-///     (ConnectionSize, unconnected-only, etc.) per decision #9.</param>
-/// <param name="AbServerPlcArg">The value passed to <c>ab_server --plc &lt;arg&gt;</c>. Some families
-///     map 1:1 (ControlLogix → "controllogix"); Micro800/GuardLogix fall back to the family whose
-///     CIP behavior ab_server emulates most faithfully (see per-profile Notes).</param>
-/// <param name="SeedTags">Tags to preseed on the simulator via <c>--tag &lt;name&gt;:&lt;type&gt;[:&lt;size&gt;]</c>
-///     flags. Each entry becomes one CLI arg; the driver-side <see cref="AbCipTagDefinition"/>
-///     list references the same names so tests can read/write without walking the @tags surface
-///     first.</param>
-/// <param name="Notes">Operator-facing description of what the profile covers + any quirks.</param>
+/// <param name="Family">OtOpcUa driver family this profile targets.</param>
+/// <param name="ComposeProfile">The <c>docker compose --profile</c> name that brings
+///     this family's ab_server up. Matches the service key in the compose file.</param>
+/// <param name="Notes">Operator-facing description of coverage + any quirks.</param>
 public sealed record AbServerProfile(
     AbCipPlcFamily Family,
-    string AbServerPlcArg,
-    IReadOnlyList<AbServerSeedTag> SeedTags,
+    string ComposeProfile,
     string Notes)
 {
-    /// <summary>Default port — every profile uses the same so parallel-runs-of-different-families
-    /// would conflict (deliberately — one simulator per test collection is the model).</summary>
+    /// <summary>Default ab_server port — matches the compose-file port-map + the
+    /// CIP / EtherNet/IP standard.</summary>
     public const int DefaultPort = 44818;
-
-    /// <summary>Compose the full <c>ab_server</c> CLI arg string for
-    /// <see cref="System.Diagnostics.ProcessStartInfo.Arguments"/>.</summary>
-    public string BuildCliArgs(int port)
-    {
-        var parts = new List<string>
-        {
-            "--port", port.ToString(),
-            "--plc", AbServerPlcArg,
-        };
-        foreach (var tag in SeedTags)
-        {
-            parts.Add("--tag");
-            parts.Add(tag.ToCliSpec());
-        }
-        return string.Join(' ', parts);
-    }
-}
-
-/// <summary>One tag the simulator pre-creates. ab_server spec format:
-/// <c>&lt;name&gt;:&lt;type&gt;[:&lt;array_size&gt;]</c>.</summary>
-public sealed record AbServerSeedTag(string Name, string AbServerType, int? ArraySize = null)
-{
-    public string ToCliSpec() => ArraySize is { } n ? $"{Name}:{AbServerType}:{n}" : $"{Name}:{AbServerType}";
 }
 
 /// <summary>Canonical profiles covering every AB CIP family shipped in PRs 9–12.</summary>
 public static class KnownProfiles
 {
-    /// <summary>
-    ///     ControlLogix — the widest-coverage family: full CIP capabilities, generous connection
-    ///     size, @tags controller-walk supported. Tag shape covers atomic types + a Program-scoped
-    ///     tag so the Symbol-Object decoder's scope-split path is exercised.
-    /// </summary>
     public static readonly AbServerProfile ControlLogix = new(
         Family: AbCipPlcFamily.ControlLogix,
-        AbServerPlcArg: "controllogix",
-        SeedTags: new AbServerSeedTag[]
-        {
-            new("TestDINT",  "DINT"),
-            new("TestREAL",  "REAL"),
-            new("TestBOOL",  "BOOL"),
-            new("TestSINT",  "SINT"),
-            new("TestString","STRING"),
-            new("TestArray", "DINT", ArraySize: 16),
-        },
-        Notes: "Widest-coverage profile — PR 9 baseline. UDTs live in PR 6-shipped Template Object tests; ab_server lacks full UDT emulation.");
+        ComposeProfile: "controllogix",
+        Notes: "Widest-coverage profile — PR 9 baseline. UDTs unit-tested via golden Template Object buffers; ab_server lacks full UDT emulation.");
 
-    /// <summary>
-    ///     CompactLogix — narrower ConnectionSize quirk exercised here. ab_server doesn't
-    ///     enforce the narrower limit itself; the driver-side profile caps it + this simulator
-    ///     honors whatever the client asks for. Tag set is a subset of ControlLogix.
-    /// </summary>
     public static readonly AbServerProfile CompactLogix = new(
         Family: AbCipPlcFamily.CompactLogix,
-        AbServerPlcArg: "compactlogix",
-        SeedTags: new AbServerSeedTag[]
-        {
-            new("TestDINT",  "DINT"),
-            new("TestREAL",  "REAL"),
-            new("TestBOOL",  "BOOL"),
-        },
-        Notes: "Narrower ConnectionSize than ControlLogix — driver-side profile caps it per PR 10. Tag set mirrors the CompactLogix atomic subset.");
+        ComposeProfile: "compactlogix",
+        Notes: "ab_server doesn't enforce the narrower ConnectionSize; driver-side profile caps it per PR 10.");
 
-    /// <summary>
-    ///     Micro800 — unconnected-only family. ab_server has no explicit micro800 plc mode so
-    ///     we fall back to the nearest CIP-compatible emulation (controllogix) + document the
-    ///     discrepancy. Driver-side path enforcement (empty routing path, unconnected-only
-    ///     sessions) is exercised in the unit suite; this integration profile smoke-tests that
-    ///     reads work end-to-end against the unconnected path.
-    /// </summary>
     public static readonly AbServerProfile Micro800 = new(
         Family: AbCipPlcFamily.Micro800,
-        AbServerPlcArg: "controllogix", // ab_server lacks dedicated micro800 mode — see Notes
-        SeedTags: new AbServerSeedTag[]
-        {
-            new("TestDINT",  "DINT"),
-            new("TestREAL",  "REAL"),
-        },
-        Notes: "ab_server has no --plc micro800 — falls back to controllogix emulation. Driver side still enforces empty path + unconnected-only per PR 11. Real Micro800 coverage requires a 2080 on a lab rig.");
+        ComposeProfile: "micro800",
+        Notes: "--plc=Micro800 mode (unconnected-only, empty path). Driver-side enforcement verified in the unit suite.");
 
-    /// <summary>
-    ///     GuardLogix — safety-capable ControlLogix variant with ViewOnly safety tags. ab_server
-    ///     doesn't emulate the safety subsystem; we preseed a safety-suffixed name (<c>_S</c>) so
-    ///     the driver's read-only classification path is exercised against a real tag.
-    /// </summary>
     public static readonly AbServerProfile GuardLogix = new(
         Family: AbCipPlcFamily.GuardLogix,
-        AbServerPlcArg: "controllogix",
-        SeedTags: new AbServerSeedTag[]
-        {
-            new("TestDINT",  "DINT"),
-            new("SafetyDINT_S", "DINT"), // _S-suffixed → driver classifies as safety-ViewOnly per PR 12
-        },
-        Notes: "ab_server has no safety subsystem — this profile emulates the tag-naming contract. Real safety-lock behavior requires a physical GuardLogix 1756-L8xS rig.");
+        ComposeProfile: "guardlogix",
+        Notes: "ab_server has no safety subsystem — _S-suffixed seed tag triggers driver-side ViewOnly classification only.");
 
     public static IReadOnlyList<AbServerProfile> All { get; } =
-        new[] { ControlLogix, CompactLogix, Micro800, GuardLogix };
+        [ControlLogix, CompactLogix, Micro800, GuardLogix];
 
     public static AbServerProfile ForFamily(AbCipPlcFamily family) =>
         All.FirstOrDefault(p => p.Family == family)

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbServerProfileGate.cs

@@ -0,0 +1,52 @@
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests;
+
+/// <summary>
+///     Runtime gate that lets an integration-test class declare which target-server tier
+///     it requires. Reads <c>AB_SERVER_PROFILE</c> from the environment; tests call
+///     <see cref="SkipUnless"/> with the profile names they support + skip otherwise.
+/// </summary>
+/// <remarks>
+///     <para>Two tiers today:</para>
+///     <list type="bullet">
+///       <item><c>abserver</c> (default) — the Dockerized libplctag <c>ab_server</c>
+///         simulator. Covers atomic reads / writes / basic discovery across the four
+///         families (ControlLogix / CompactLogix / Micro800 / GuardLogix).</item>
+///       <item><c>emulate</c> — Rockwell Studio 5000 Logix Emulate on an operator's
+///         Windows box, exposed via <c>AB_SERVER_ENDPOINT</c>. Adds real UDT / ALMD /
+///         AOI / Program-scoped-tag coverage that ab_server can't emulate. Tier-gated
+///         because Emulate is per-seat licensed + Windows-only + manually launched;
+///         a stock `dotnet test` run against ab_server must skip Emulate-only classes
+///         cleanly.</item>
+///     </list>
+///     <para>Tests assert their target tier at the top of each <c>[Fact]</c> /
+///     <c>[Theory]</c> body, mirroring the <c>MODBUS_SIM_PROFILE</c> gate pattern in
+///     <c>tests/.../Modbus.IntegrationTests/DL205/DL205StringQuirkTests.cs</c>.</para>
+/// </remarks>
+public static class AbServerProfileGate
+{
+    public const string Default = "abserver";
+    public const string Emulate = "emulate";
+
+    /// <summary>Active profile from <c>AB_SERVER_PROFILE</c>; defaults to <see cref="Default"/>.</summary>
+    public static string CurrentProfile =>
+        Environment.GetEnvironmentVariable("AB_SERVER_PROFILE") is { Length: > 0 } raw
+            ? raw.Trim().ToLowerInvariant()
+            : Default;
+
+    /// <summary>
+    ///     Skip the calling test via <c>Assert.Skip</c> when <see cref="CurrentProfile"/>
+    ///     isn't in <paramref name="requiredProfiles"/>. Case-insensitive match.
+    /// </summary>
+    public static void SkipUnless(params string[] requiredProfiles)
+    {
+        foreach (var p in requiredProfiles)
+            if (string.Equals(p, CurrentProfile, StringComparison.OrdinalIgnoreCase))
+                return;
+        Assert.Skip(
+            $"Test requires AB_SERVER_PROFILE in {{{string.Join(", ", requiredProfiles)}}}; " +
+            $"current value is '{CurrentProfile}'. " +
+            $"Set AB_SERVER_PROFILE=emulate + point AB_SERVER_ENDPOINT at a Logix Emulate instance to run the golden-box-tier tests.");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbServerProfileTests.cs

@@ -5,61 +5,23 @@ using ZB.MOM.WW.OtOpcUa.Driver.AbCip;
 namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests;
 
 /// <summary>
-///     Pure-unit tests for the profile → CLI arg composition. Runs without <c>ab_server</c>
-///     on PATH so CI without the binary still exercises these contracts + catches any
-///     profile-definition drift (e.g. a typo in <c>--plc</c> mapping would silently make the
-///     simulator boot with the wrong family).
+///     Pure-unit tests for the profile catalog. Verifies <see cref="KnownProfiles"/>
+///     stays in sync with <see cref="AbCipPlcFamily"/> + with the compose-file service
+///     names — a typo in either would surface as a test failure rather than a silent
+///     "wrong family booted" at runtime. Runs without Docker, so CI without the
+///     container still exercises these contracts.
 /// </summary>
 [Trait("Category", "Unit")]
 public sealed class AbServerProfileTests
 {
-    [Fact]
-    public void BuildCliArgs_Emits_Port_And_Plc_And_TagFlags()
-    {
-        var profile = new AbServerProfile(
-            Family: AbCipPlcFamily.ControlLogix,
-            AbServerPlcArg: "controllogix",
-            SeedTags: new AbServerSeedTag[]
-            {
-                new("A", "DINT"),
-                new("B", "REAL"),
-            },
-            Notes: "test");
-
-        profile.BuildCliArgs(44818).ShouldBe("--port 44818 --plc controllogix --tag A:DINT --tag B:REAL");
-    }
-
-    [Fact]
-    public void BuildCliArgs_NoSeedTags_Emits_Just_Port_And_Plc()
-    {
-        var profile = new AbServerProfile(
-            AbCipPlcFamily.ControlLogix, "controllogix", [], "empty");
-
-        profile.BuildCliArgs(5000).ShouldBe("--port 5000 --plc controllogix");
-    }
-
-    [Fact]
-    public void AbServerSeedTag_ArraySize_FormatsAsThirdSegment()
-    {
-        new AbServerSeedTag("TestArray", "DINT", ArraySize: 16)
-            .ToCliSpec().ShouldBe("TestArray:DINT:16");
-    }
-
-    [Fact]
-    public void AbServerSeedTag_NoArraySize_TwoSegments()
-    {
-        new AbServerSeedTag("TestScalar", "REAL")
-            .ToCliSpec().ShouldBe("TestScalar:REAL");
-    }
-
     [Theory]
     [InlineData(AbCipPlcFamily.ControlLogix, "controllogix")]
     [InlineData(AbCipPlcFamily.CompactLogix, "compactlogix")]
-    [InlineData(AbCipPlcFamily.Micro800,     "controllogix")] // falls back — ab_server lacks dedicated mode
-    [InlineData(AbCipPlcFamily.GuardLogix,   "controllogix")] // falls back — ab_server lacks safety subsystem
-    public void KnownProfiles_ForFamily_Returns_Expected_AbServerPlcArg(AbCipPlcFamily family, string expected)
+    [InlineData(AbCipPlcFamily.Micro800,     "micro800")]
+    [InlineData(AbCipPlcFamily.GuardLogix,   "guardlogix")]
+    public void KnownProfiles_ForFamily_Returns_Expected_ComposeProfile(AbCipPlcFamily family, string expected)
     {
-        KnownProfiles.ForFamily(family).AbServerPlcArg.ShouldBe(expected);
+        KnownProfiles.ForFamily(family).ComposeProfile.ShouldBe(expected);
     }
 
     [Fact]
@@ -71,20 +33,8 @@ public sealed class AbServerProfileTests
     }
 
     [Fact]
-    public void KnownProfiles_ControlLogix_Includes_AllAtomicTypes()
+    public void DefaultPort_Matches_EtherNetIP_Standard()
     {
-        var tags = KnownProfiles.ControlLogix.SeedTags.Select(t => t.AbServerType).ToHashSet();
-        tags.ShouldContain("DINT");
-        tags.ShouldContain("REAL");
-        tags.ShouldContain("BOOL");
-        tags.ShouldContain("SINT");
-        tags.ShouldContain("STRING");
-    }
-
-    [Fact]
-    public void KnownProfiles_GuardLogix_SeedsSafetySuffixedTag()
-    {
-        KnownProfiles.GuardLogix.SeedTags
-            .ShouldContain(t => t.Name.EndsWith("_S"), "GuardLogix profile must seed at least one _S-suffixed tag for safety-classification coverage.");
+        AbServerProfile.DefaultPort.ShouldBe(44818);
     }
 }

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/Dockerfile

@@ -0,0 +1,43 @@
+# ab_server container for the AB CIP integration suite.
+#
+# ab_server is a C program in libplctag/libplctag under src/tools/ab_server.
+# We clone at a pinned commit, build just the ab_server target via CMake,
+# and copy the resulting binary into a slim runtime stage so the published
+# image stays small (~60MB vs ~350MB for the build stage).
+
+# -------- stage 1: build ab_server from source --------
+FROM debian:bookworm-slim AS build
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        git \
+        build-essential \
+        cmake \
+        ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+# Pinned tag matches the `ab_server` version AbServerFixture + CI treat as
+# canonical. Bump deliberately alongside a driver-side change that needs
+# something newer.
+ARG LIBPLCTAG_TAG=release
+RUN git clone --depth 1 --branch "${LIBPLCTAG_TAG}" https://github.com/libplctag/libplctag.git /src
+
+WORKDIR /src
+RUN cmake -S . -B build -DCMAKE_BUILD_TYPE=Release \
+ && cmake --build build --target ab_server --parallel
+
+# -------- stage 2: runtime --------
+FROM debian:bookworm-slim
+
+LABEL org.opencontainers.image.source="https://github.com/dohertj2/lmxopcua" \
+      org.opencontainers.image.description="libplctag ab_server for OtOpcUa AB CIP driver integration tests"
+
+# libplctag's ab_server is statically linked against libc / libstdc++ on
+# Debian bookworm; no runtime dependencies beyond what the slim image
+# already has.
+COPY --from=build /src/build/bin_dist/ab_server /usr/local/bin/ab_server
+
+EXPOSE 44818
+
+# docker-compose.yml overrides the command with per-family flags.
+CMD ["ab_server", "--plc=ControlLogix", "--path=1,0", "--port=44818", \
+     "--tag=TestDINT:DINT[1]", "--tag=TestREAL:REAL[1]", "--tag=TestBOOL:BOOL[1]"]

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/README.md

@@ -0,0 +1,89 @@
+# AB CIP integration-test fixture — `ab_server` (Docker)
+
+[libplctag](https://github.com/libplctag/libplctag)'s `ab_server` — a
+MIT-licensed C program that emulates a ControlLogix / CompactLogix CIP
+endpoint over EtherNet/IP. Docker is the only supported launch path;
+`ab_server` ships as a source-only tool under libplctag's
+`src/tools/ab_server/` so the Dockerfile's multi-stage build is the only
+reproducible way to get a working binary across developer boxes. A fresh
+clone needs Docker Desktop and nothing else.
+
+| File | Purpose |
+|---|---|
+| [`Dockerfile`](Dockerfile) | Multi-stage: build from libplctag at pinned tag → copy binary into `debian:bookworm-slim` runtime image |
+| [`docker-compose.yml`](docker-compose.yml) | One service per family (`controllogix` / `compactlogix` / `micro800` / `guardlogix`); all bind `:44818` |
+
+## Run
+
+From the repo root:
+
+```powershell
+# ControlLogix — widest-coverage profile
+docker compose -f tests\ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests\Docker\docker-compose.yml --profile controllogix up
+
+# Per-family
+docker compose -f tests\...\Docker\docker-compose.yml --profile compactlogix up
+docker compose -f tests\...\Docker\docker-compose.yml --profile micro800 up
+docker compose -f tests\...\Docker\docker-compose.yml --profile guardlogix up
+```
+
+Detached + stop:
+
+```powershell
+docker compose -f tests\...\Docker\docker-compose.yml --profile controllogix up -d
+docker compose -f tests\...\Docker\docker-compose.yml --profile controllogix down
+```
+
+First run builds the image (~3-5 minutes — clones libplctag + compiles
+`ab_server` + its dependencies). Subsequent runs are fast because the
+multi-stage build layer-caches the checkout + compile.
+
+## Endpoint
+
+- Default: `localhost:44818` (EtherNet/IP standard; non-privileged)
+- Override with `AB_SERVER_ENDPOINT=host:port` to point at a real PLC.
+
+## Run the integration tests
+
+In a separate shell with a container up:
+
+```powershell
+cd C:\Users\dohertj2\Desktop\lmxopcua
+dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests
+```
+
+`AbServerFixture` TCP-probes `localhost:44818` at collection init +
+records a skip reason when unreachable, so tests stay green on a fresh
+clone without the container running. Tests use `[AbServerFact]` /
+`[AbServerTheory]` which check the same probe.
+
+## What each family seeds
+
+Tag sets match `AbServerProfile.cs` exactly — changing seeds in one
+place means updating both.
+
+| Family | Seeded tags | Notes |
+|---|---|---|
+| ControlLogix | `TestDINT` `TestREAL` `TestBOOL` `TestSINT` `TestString` `TestArray` | Widest-coverage; PR 9 baseline. UDT emulation missing from ab_server |
+| CompactLogix | `TestDINT` `TestREAL` `TestBOOL` | Narrow ConnectionSize cap enforced driver-side; ab_server accepts any size |
+| Micro800 | `TestDINT` `TestREAL` | ab_server has no `micro800` mode; falls back to `controllogix` emulation |
+| GuardLogix | `TestDINT` `SafetyDINT_S` | ab_server has no safety subsystem; `_S` suffix triggers driver-side classification only |
+
+## Known limitations
+
+- **No UDT / CIP Template Object emulation** — `ab_server` covers atomic
+  types only. UDT reads + task #194 whole-UDT optimization verify via
+  unit tests with golden byte buffers.
+- **Family-specific quirks trust driver-side code** — ab_server emulates
+  a generic Logix CPU; the ConnectionSize cap, empty-path unconnected
+  mode, and safety-partition write rejection all need lab rigs for
+  wire-level proof.
+
+See [`docs/drivers/AbServer-Test-Fixture.md`](../../../docs/drivers/AbServer-Test-Fixture.md)
+for the full coverage map.
+
+## References
+
+- [libplctag on GitHub](https://github.com/libplctag/libplctag)
+- [`docs/drivers/AbServer-Test-Fixture.md`](../../../docs/drivers/AbServer-Test-Fixture.md) — coverage map
+- [`docs/v2/dev-environment.md`](../../../docs/v2/dev-environment.md) §Docker fixtures

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/docker-compose.yml

@@ -0,0 +1,97 @@
+# AB CIP integration-test fixture — ab_server (libplctag).
+#
+# One service per family. All bind :44818 on the host; only one runs at a
+# time. Commands mirror the CLI args AbServerProfile.cs constructs for the
+# native-binary path.
+#
+# Usage:
+#   docker compose --profile controllogix up
+#   docker compose --profile compactlogix up
+#   docker compose --profile micro800 up
+#   docker compose --profile guardlogix up
+services:
+  controllogix:
+    profiles: ["controllogix"]
+    build:
+      context: .
+      dockerfile: Dockerfile
+    image: otopcua-ab-server:libplctag-release
+    container_name: otopcua-ab-server-controllogix
+    restart: "no"
+    ports:
+      - "44818:44818"
+    command: [
+      "ab_server",
+      "--plc=ControlLogix",
+      "--path=1,0",
+      "--port=44818",
+      "--tag=TestDINT:DINT[1]",
+      "--tag=TestREAL:REAL[1]",
+      "--tag=TestBOOL:BOOL[1]",
+      "--tag=TestSINT:SINT[1]",
+      "--tag=TestString:STRING[1]",
+      "--tag=TestArray:DINT[16]"
+    ]
+
+  compactlogix:
+    profiles: ["compactlogix"]
+    image: otopcua-ab-server:libplctag-release
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: otopcua-ab-server-compactlogix
+    restart: "no"
+    ports:
+      - "44818:44818"
+    # ab_server doesn't distinguish CompactLogix from ControlLogix — no
+    # dedicated --plc mode. Driver-side ConnectionSize cap is enforced
+    # separately (see AbServerProfile.CompactLogix Notes).
+    command: [
+      "ab_server",
+      "--plc=ControlLogix",
+      "--path=1,0",
+      "--port=44818",
+      "--tag=TestDINT:DINT[1]",
+      "--tag=TestREAL:REAL[1]",
+      "--tag=TestBOOL:BOOL[1]"
+    ]
+
+  micro800:
+    profiles: ["micro800"]
+    image: otopcua-ab-server:libplctag-release
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: otopcua-ab-server-micro800
+    restart: "no"
+    ports:
+      - "44818:44818"
+    # ab_server does have a Micro800 plc mode (unconnected-only, empty path).
+    command: [
+      "ab_server",
+      "--plc=Micro800",
+      "--port=44818",
+      "--tag=TestDINT:DINT[1]",
+      "--tag=TestREAL:REAL[1]"
+    ]
+
+  guardlogix:
+    profiles: ["guardlogix"]
+    image: otopcua-ab-server:libplctag-release
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: otopcua-ab-server-guardlogix
+    restart: "no"
+    ports:
+      - "44818:44818"
+    # ab_server has no safety subsystem — _S suffix triggers driver-side
+    # classification only.
+    command: [
+      "ab_server",
+      "--plc=ControlLogix",
+      "--path=1,0",
+      "--port=44818",
+      "--tag=TestDINT:DINT[1]",
+      "--tag=SafetyDINT_S:DINT[1]"
+    ]

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Emulate/AbCipEmulateAlmdTests.cs

@@ -0,0 +1,105 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.Emulate;
+
+/// <summary>
+///     Golden-box-tier ALMD alarm projection tests against Logix Emulate.
+///     Promotes the feature-flagged ALMD projection (task #177) from unit-only coverage
+///     (<c>AbCipAlarmProjectionTests</c> with faked InFaulted sequences) to end-to-end
+///     wire-level coverage — Emulate runs the real ALMD instruction, with real
+///     rising-edge semantics on <c>InFaulted</c> + <c>Ack</c>, so the driver's poll-based
+///     projection gets validated against the actual behaviour shops running FT View see.
+/// </summary>
+/// <remarks>
+///     <para><b>Required Emulate project state</b> (see <c>LogixProject/README.md</c>):</para>
+///     <list type="bullet">
+///       <item>Controller-scope ALMD tag <c>HighTempAlarm</c> — a standard ALMD instruction
+///         with default member set (<c>In</c>, <c>InFaulted</c>, <c>Acked</c>,
+///         <c>Severity</c>, <c>Cfg_ProgTime</c>, …).</item>
+///       <item>A periodic task that drives <c>HighTempAlarm.In</c> false→true→false at a
+///         cadence the operator can script via a one-shot routine (e.g. a
+///         <c>SimulateAlarm</c> bit the test case pulses through
+///         <c>IWritable.WriteAsync</c>).</item>
+///       <item>Operator writes <c>1</c> to <c>SimulateAlarm</c> to trigger the rising
+///         edge on <c>HighTempAlarm.In</c>; ladder uses that as the alarm input.</item>
+///     </list>
+///     <para>Runs only when <c>AB_SERVER_PROFILE=emulate</c>. ab_server has no ALMD
+///     instruction + no alarm subsystem, so this tier-gated class couldn't produce a
+///     meaningful result against the default simulator.</para>
+/// </remarks>
+[Collection("AbServerEmulate")]
+[Trait("Category", "Integration")]
+[Trait("Tier", "Emulate")]
+public sealed class AbCipEmulateAlmdTests
+{
+    [AbServerFact]
+    public async Task Real_ALMD_raise_fires_OnAlarmEvent_through_the_driver_projection()
+    {
+        AbServerProfileGate.SkipUnless(AbServerProfileGate.Emulate);
+
+        var endpoint = Environment.GetEnvironmentVariable("AB_SERVER_ENDPOINT")
+            ?? throw new InvalidOperationException(
+                "AB_SERVER_ENDPOINT must be set to the Logix Emulate instance when AB_SERVER_PROFILE=emulate.");
+
+        var options = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions($"ab://{endpoint}/1,0")],
+            EnableAlarmProjection = true,
+            AlarmPollInterval = TimeSpan.FromMilliseconds(200),
+            Tags = [
+                new AbCipTagDefinition(
+                    Name: "HighTempAlarm",
+                    DeviceHostAddress: $"ab://{endpoint}/1,0",
+                    TagPath: "HighTempAlarm",
+                    DataType: AbCipDataType.Structure,
+                    Members: [
+                        new AbCipStructureMember("InFaulted", AbCipDataType.DInt),
+                        new AbCipStructureMember("Acked",     AbCipDataType.DInt),
+                        new AbCipStructureMember("Severity",  AbCipDataType.DInt),
+                        new AbCipStructureMember("In",        AbCipDataType.DInt),
+                    ]),
+                // The "simulate the alarm input" bit the ladder watches.
+                new AbCipTagDefinition(
+                    Name: "SimulateAlarm",
+                    DeviceHostAddress: $"ab://{endpoint}/1,0",
+                    TagPath: "SimulateAlarm",
+                    DataType: AbCipDataType.Bool,
+                    Writable: true),
+            ],
+        };
+
+        await using var drv = new AbCipDriver(options, driverInstanceId: "emulate-almd");
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        var raised = new TaskCompletionSource<AlarmEventArgs>(TaskCreationOptions.RunContinuationsAsynchronously);
+        drv.OnAlarmEvent += (_, e) =>
+        {
+            if (e.Message.Contains("raised")) raised.TrySetResult(e);
+        };
+
+        var sub = await drv.SubscribeAlarmsAsync(
+            ["HighTempAlarm"], TestContext.Current.CancellationToken);
+
+        // Pulse the input bit the ladder watches, then wait for the driver's poll loop
+        // to see InFaulted rise + fire the raise event.
+        _ = await drv.WriteAsync(
+            [new WriteRequest("SimulateAlarm", true)],
+            TestContext.Current.CancellationToken);
+
+        var got = await Task.WhenAny(raised.Task, Task.Delay(TimeSpan.FromSeconds(5)));
+        got.ShouldBe(raised.Task, "driver must surface the ALMD raise within 5 s of the ladder-driven edge");
+        var args = await raised.Task;
+        args.SourceNodeId.ShouldBe("HighTempAlarm");
+        args.AlarmType.ShouldBe("ALMD");
+
+        await drv.UnsubscribeAlarmsAsync(sub, TestContext.Current.CancellationToken);
+
+        // Reset the bit so the next test run starts from a known state.
+        _ = await drv.WriteAsync(
+            [new WriteRequest("SimulateAlarm", false)],
+            TestContext.Current.CancellationToken);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Emulate/AbCipEmulateUdtReadTests.cs

@@ -0,0 +1,81 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.Emulate;
+
+/// <summary>
+///     Golden-box-tier UDT read tests against Rockwell Studio 5000 Logix Emulate.
+///     Promotes the whole-UDT-read optimization (task #194) from unit-only coverage
+///     (golden Template Object byte buffers + <see cref="AbCipUdtMemberLayoutTests"/>)
+///     to end-to-end wire-level coverage — Emulate's firmware speaks the same CIP
+///     Template Object responses real hardware does, so the member-offset math + the
+///     <c>AbCipUdtReadPlanner</c> grouping get validated against production semantics.
+/// </summary>
+/// <remarks>
+///     <para><b>Required Emulate project state</b> (see <c>LogixProject/README.md</c>
+///     for the L5X export that seeds this; ship the project once Emulate is on the
+///     integration host):</para>
+///     <list type="bullet">
+///       <item>UDT <c>Motor_UDT</c> with members <c>Speed : DINT</c>, <c>Torque : REAL</c>,
+///         <c>Status : DINT</c> — the member set <see cref="AbCipUdtMemberLayoutTests"/>
+///         uses as its declared-layout golden reference.</item>
+///       <item>Controller-scope tag <c>Motor1 : Motor_UDT</c> with seed values
+///         Speed=<c>1800</c>, Torque=<c>42.5f</c>, Status=<c>0x0001</c>.</item>
+///     </list>
+///     <para>Runs only when <c>AB_SERVER_PROFILE=emulate</c>. With ab_server
+///     (the default), skips cleanly — ab_server lacks UDT / Template Object emulation
+///     so this wire-level test couldn't pass against it regardless.</para>
+/// </remarks>
+[Collection("AbServerEmulate")]
+[Trait("Category", "Integration")]
+[Trait("Tier", "Emulate")]
+public sealed class AbCipEmulateUdtReadTests
+{
+    [AbServerFact]
+    public async Task WholeUdt_read_decodes_each_member_at_its_Template_Object_offset()
+    {
+        AbServerProfileGate.SkipUnless(AbServerProfileGate.Emulate);
+
+        var endpoint = Environment.GetEnvironmentVariable("AB_SERVER_ENDPOINT")
+            ?? throw new InvalidOperationException(
+                "AB_SERVER_ENDPOINT must be set to the Logix Emulate instance " +
+                "(e.g. '10.0.0.42:44818') when AB_SERVER_PROFILE=emulate.");
+
+        var options = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions($"ab://{endpoint}/1,0")],
+            Tags = [
+                new AbCipTagDefinition(
+                    Name: "Motor1",
+                    DeviceHostAddress: $"ab://{endpoint}/1,0",
+                    TagPath: "Motor1",
+                    DataType: AbCipDataType.Structure,
+                    Members: [
+                        new AbCipStructureMember("Speed",  AbCipDataType.DInt),
+                        new AbCipStructureMember("Torque", AbCipDataType.Real),
+                        new AbCipStructureMember("Status", AbCipDataType.DInt),
+                    ]),
+            ],
+            Timeout = TimeSpan.FromSeconds(5),
+        };
+
+        await using var drv = new AbCipDriver(options, driverInstanceId: "emulate-udt-smoke");
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        // Whole-UDT read optimization from task #194: one libplctag read on the
+        // parent tag, three decodes from the buffer at member offsets. Asserts
+        // Emulate's Template Object response matches what AbCipUdtMemberLayout
+        // computes from the declared member set.
+        var snapshots = await drv.ReadAsync(
+            ["Motor1.Speed", "Motor1.Torque", "Motor1.Status"],
+            TestContext.Current.CancellationToken);
+
+        snapshots.Count.ShouldBe(3);
+        foreach (var s in snapshots) s.StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        Convert.ToInt32(snapshots[0].Value).ShouldBe(1800);
+        Convert.ToSingle(snapshots[1].Value).ShouldBe(42.5f, tolerance: 0.001f);
+        Convert.ToInt32(snapshots[2].Value).ShouldBe(0x0001);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/LogixProject/README.md

@@ -0,0 +1,102 @@
+# Logix Emulate project stub
+
+This folder holds the Studio 5000 project that Logix Emulate loads when running
+the Emulate-tier integration tests
+(`tests/.../AbCip.IntegrationTests/Emulate/*.cs`, gated on
+`AB_SERVER_PROFILE=emulate`).
+
+**Status today**: stub. The actual `.L5X` export isn't committed yet; once
+the Emulate PC is running + a project with the required state exists,
+export to L5X + drop it here as `OtOpcUaAbCipFixture.L5X`.
+
+## Why L5X, not .ACD
+
+Studio 5000 ships two save formats: `.ACD` (binary, the runtime project)
+and `.L5X` (XML export). Ship the L5X because:
+
+- Text format — reviewable in PR diffs, diffable in git
+- Reproducible import across Studio 5000 versions
+- Doesn't carry per-installation state (license watermarks, revision history)
+
+Reconstruction workflow: Studio 5000 → open project → File → Save As
+→ `.L5X`. On a fresh Emulate install: File → Open → select the L5X → it
+rebuilds the ACD from the XML.
+
+## Required project state
+
+The Emulate-tier tests rely on this exact tag / UDT set. Missing any of
+these makes the dependent test fail loudly (TagNotFound, wrong value,
+wrong type), not skip silently — Emulate is a tier above the Docker
+simulator; operators who opted into it get opt-in-level coverage
+expectations.
+
+### UDT definitions
+
+| UDT name | Members | Notes |
+|---|---|---|
+| `Motor_UDT` | `Speed : DINT`, `Torque : REAL`, `Status : DINT` | Matches `AbCipUdtMemberLayoutTests` declared-layout golden. Member order fixed — Logix Template Object offsets depend on it |
+
+### Controller tags
+
+| Tag | Type | Seed value | Purpose |
+|---|---|---|---|
+| `Motor1` | `Motor_UDT` | `{Speed=1800, Torque=42.5, Status=0x0001}` | `AbCipEmulateUdtReadTests.WholeUdt_read_decodes_each_member_at_its_Template_Object_offset` |
+| `HighTempAlarm` | `ALMD` | default ALMD config, `In` tied to `SimulateAlarm` bit | `AbCipEmulateAlmdTests.Real_ALMD_raise_fires_OnAlarmEvent_through_the_driver_projection` |
+| `SimulateAlarm` | `BOOL` | `0` | Operator-writable bit the ladder routes into `HighTempAlarm.In` — gives the test a clean way to drive the alarm edge without scripting Emulate directly |
+
+### Program structure
+
+- One periodic task `MainTask` @ 100 ms
+- One program `MainProgram`
+- One routine `MainRoutine` (Ladder) with a single rung:
+  `XIC SimulateAlarm OTE HighTempAlarm.In`
+
+That's enough ladder for `SimulateAlarm := 1` to raise the alarm + for
+`SimulateAlarm := 0` to clear it.
+
+## Tier-level behaviours this project enables
+
+Coverage the existing Dockerized `ab_server` fixture can't produce —
+each verified by an `Emulate/*Tests.cs` class gated on
+`AB_SERVER_PROFILE=emulate`:
+
+- **CIP Template Object round-trip** — real Logix template bytes,
+  reads produce the same offset layout the CIP Symbol Object decoder +
+  `AbCipUdtMemberLayout` expect.
+- **ALMD rising-edge semantics** — real Logix ALMD instruction fires
+  `InFaulted` / `Acked` transitions at cycle boundaries, not at our
+  unit-test fake's timer boundaries.
+- **Optimized vs unoptimized DB behaviour** — Logix 5380/5580 series
+  runs the Studio 5000 project with optimized-DB-equivalent member
+  access; the driver's read path exercises that wire surface.
+
+Not in scope even with Emulate — needs real hardware:
+
+- EtherNet/IP embedded-switch behaviour (Stratix 5700, 1756-EN4TR)
+- CIP Safety across partitions (Emulate 5580 emulates safety within
+  the chassis but not across nodes)
+- Redundant chassis failover (1756-RM)
+- Motion control timing
+- High-speed discrete-input scheduling
+
+## How to run the Emulate-tier tests
+
+On the dev box:
+
+```powershell
+$env:AB_SERVER_PROFILE  = 'emulate'
+$env:AB_SERVER_ENDPOINT = '10.0.0.42:44818'   # replace with the Emulate PC IP
+dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests
+```
+
+With `AB_SERVER_PROFILE` unset or `abserver`, the `Emulate/*Tests.cs`
+classes skip cleanly; ab_server-backed tests run as usual.
+
+## See also
+
+- [`docs/drivers/AbServer-Test-Fixture.md`](../../../docs/drivers/AbServer-Test-Fixture.md)
+  §Logix Emulate golden-box tier — coverage map
+- [`docs/v2/dev-environment.md`](../../../docs/v2/dev-environment.md)
+  §Integration host — license + networking notes
+- Studio 5000 Logix Designer + Logix Emulate product pages on the
+  Rockwell TechConnect portal (licensed; internal link only).

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.csproj

@@ -23,6 +23,11 @@
         <ProjectReference Include="..\..\src\ZB.MOM.WW.OtOpcUa.Driver.AbCip\ZB.MOM.WW.OtOpcUa.Driver.AbCip.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <None Update="Docker\**\*" CopyToOutputDirectory="PreserveNewest"/>
+        <None Update="LogixProject\**\*" CopyToOutputDirectory="PreserveNewest"/>
+    </ItemGroup>
+
     <ItemGroup>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipAlarmProjectionTests.cs

@@ -0,0 +1,190 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+/// <summary>
+///     Task #177 — tests covering ALMD projection detection, feature-flag gate,
+///     subscribe/unsubscribe lifecycle, state-transition event emission, and acknowledge.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class AbCipAlarmProjectionTests
+{
+    private const string Device = "ab://10.0.0.5/1,0";
+
+    private static AbCipTagDefinition AlmdTag(string name) => new(
+        name, Device, name, AbCipDataType.Structure, Members:
+        [
+            new AbCipStructureMember("InFaulted", AbCipDataType.DInt), // Logix stores ALMD bools as DINT
+            new AbCipStructureMember("Acked", AbCipDataType.DInt),
+            new AbCipStructureMember("Severity", AbCipDataType.DInt),
+            new AbCipStructureMember("In", AbCipDataType.DInt),
+        ]);
+
+    [Fact]
+    public void AbCipAlarmDetector_Flags_AlmdSignature_As_Alarm()
+    {
+        var almd = AlmdTag("HighTemp");
+        AbCipAlarmDetector.IsAlmd(almd).ShouldBeTrue();
+
+        var plainUdt = new AbCipTagDefinition("Plain", Device, "Plain", AbCipDataType.Structure, Members:
+            [new AbCipStructureMember("X", AbCipDataType.DInt)]);
+        AbCipAlarmDetector.IsAlmd(plainUdt).ShouldBeFalse();
+
+        var atomic = new AbCipTagDefinition("Plain", Device, "Plain", AbCipDataType.DInt);
+        AbCipAlarmDetector.IsAlmd(atomic).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void Severity_Mapping_Matches_OPC_UA_Convention()
+    {
+        // Logix severity 1–1000 — mirror the OpcUaClient ACAndC bucketing.
+        AbCipAlarmProjection.MapSeverity(100).ShouldBe(AlarmSeverity.Low);
+        AbCipAlarmProjection.MapSeverity(400).ShouldBe(AlarmSeverity.Medium);
+        AbCipAlarmProjection.MapSeverity(600).ShouldBe(AlarmSeverity.High);
+        AbCipAlarmProjection.MapSeverity(900).ShouldBe(AlarmSeverity.Critical);
+    }
+
+    [Fact]
+    public async Task FeatureFlag_Off_SubscribeAlarms_Returns_Handle_But_Never_Polls()
+    {
+        var factory = new FakeAbCipTagFactory();
+        var opts = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Device)],
+            Tags = [AlmdTag("HighTemp")],
+            EnableAlarmProjection = false, // explicit; also the default
+        };
+        var drv = new AbCipDriver(opts, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var handle = await drv.SubscribeAlarmsAsync(["HighTemp"], CancellationToken.None);
+        handle.ShouldNotBeNull();
+        handle.DiagnosticId.ShouldContain("abcip-alarm-sub-");
+
+        // Wait a touch — if polling were active, a fake member-read would be triggered.
+        await Task.Delay(100);
+        factory.Tags.ShouldNotContainKey("HighTemp.InFaulted");
+        factory.Tags.ShouldNotContainKey("HighTemp.Severity");
+
+        await drv.UnsubscribeAlarmsAsync(handle, CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task FeatureFlag_On_Subscribe_Starts_Polling_And_Fires_Raise_On_0_to_1()
+    {
+        var factory = new FakeAbCipTagFactory();
+        var opts = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Device)],
+            Tags = [AlmdTag("HighTemp")],
+            EnableAlarmProjection = true,
+            AlarmPollInterval = TimeSpan.FromMilliseconds(20),
+        };
+        var drv = new AbCipDriver(opts, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new List<AlarmEventArgs>();
+        drv.OnAlarmEvent += (_, e) => { lock (events) events.Add(e); };
+
+        var handle = await drv.SubscribeAlarmsAsync(["HighTemp"], CancellationToken.None);
+
+        // The ALMD UDT is declared so whole-UDT grouping kicks in; the parent HighTemp runtime
+        // gets created + polled. Set InFaulted offset-value to 0 first (clear), wait a tick,
+        // then flip to 1 (fault) + wait for the raise event.
+        await WaitForTagCreation(factory, "HighTemp");
+        factory.Tags["HighTemp"].ValuesByOffset[0] = 0;  // InFaulted=false at offset 0
+        factory.Tags["HighTemp"].ValuesByOffset[8] = 500; // Severity at offset 8 (after InFaulted+Acked)
+        await Task.Delay(80); // let a tick seed the "last-seen false" state
+
+        factory.Tags["HighTemp"].ValuesByOffset[0] = 1; // flip to faulted
+        await Task.Delay(200); // allow several polls to be safe
+
+        lock (events)
+        {
+            events.ShouldContain(e => e.SourceNodeId == "HighTemp" && e.AlarmType == "ALMD"
+                && e.Message.Contains("raised"));
+        }
+
+        await drv.UnsubscribeAlarmsAsync(handle, CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Clear_Event_Fires_On_1_to_0_Transition()
+    {
+        var factory = new FakeAbCipTagFactory();
+        var opts = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Device)],
+            Tags = [AlmdTag("HighTemp")],
+            EnableAlarmProjection = true,
+            AlarmPollInterval = TimeSpan.FromMilliseconds(20),
+        };
+        var drv = new AbCipDriver(opts, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new List<AlarmEventArgs>();
+        drv.OnAlarmEvent += (_, e) => { lock (events) events.Add(e); };
+
+        var handle = await drv.SubscribeAlarmsAsync(["HighTemp"], CancellationToken.None);
+        await WaitForTagCreation(factory, "HighTemp");
+
+        factory.Tags["HighTemp"].ValuesByOffset[0] = 1;
+        factory.Tags["HighTemp"].ValuesByOffset[8] = 500;
+        await Task.Delay(80); // observe raise
+
+        factory.Tags["HighTemp"].ValuesByOffset[0] = 0;
+        await Task.Delay(200);
+
+        lock (events)
+        {
+            events.ShouldContain(e => e.Message.Contains("raised"));
+            events.ShouldContain(e => e.Message.Contains("cleared"));
+        }
+
+        await drv.UnsubscribeAlarmsAsync(handle, CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Unsubscribe_Stops_The_Poll_Loop()
+    {
+        var factory = new FakeAbCipTagFactory();
+        var opts = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Device)],
+            Tags = [AlmdTag("HighTemp")],
+            EnableAlarmProjection = true,
+            AlarmPollInterval = TimeSpan.FromMilliseconds(20),
+        };
+        var drv = new AbCipDriver(opts, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var handle = await drv.SubscribeAlarmsAsync(["HighTemp"], CancellationToken.None);
+        await WaitForTagCreation(factory, "HighTemp");
+        var preUnsubReadCount = factory.Tags["HighTemp"].ReadCount;
+
+        await drv.UnsubscribeAlarmsAsync(handle, CancellationToken.None);
+        await Task.Delay(100); // well past several poll intervals if the loop were still alive
+
+        var postDelayReadCount = factory.Tags["HighTemp"].ReadCount;
+        // Allow at most one straggler read between the unsubscribe-cancel + the loop exit.
+        (postDelayReadCount - preUnsubReadCount).ShouldBeLessThanOrEqualTo(1);
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    private static async Task WaitForTagCreation(FakeAbCipTagFactory factory, string tagName)
+    {
+        var deadline = DateTime.UtcNow.AddSeconds(2);
+        while (DateTime.UtcNow < deadline)
+        {
+            if (factory.Tags.ContainsKey(tagName)) return;
+            await Task.Delay(10);
+        }
+        throw new TimeoutException($"Tag {tagName} was never created by the fake factory.");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipDriverWholeUdtReadTests.cs

@@ -0,0 +1,130 @@
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+/// <summary>
+///     Task #194 — ReadAsync integration tests for the whole-UDT grouping path. The fake
+///     runtime records ReadCount + surfaces member values by byte offset so we can assert
+///     both "one read per parent UDT" and "each member decoded at the correct offset."
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class AbCipDriverWholeUdtReadTests
+{
+    private const string Device = "ab://10.0.0.5/1,0";
+
+    private static (AbCipDriver drv, FakeAbCipTagFactory factory) NewDriver(params AbCipTagDefinition[] tags)
+    {
+        var factory = new FakeAbCipTagFactory();
+        var opts = new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Device)],
+            Tags = tags,
+        };
+        return (new AbCipDriver(opts, "drv-1", factory), factory);
+    }
+
+    private static AbCipTagDefinition MotorUdt() => new(
+        "Motor", Device, "Motor", AbCipDataType.Structure, Members:
+        [
+            new AbCipStructureMember("Speed", AbCipDataType.DInt),   // offset 0
+            new AbCipStructureMember("Torque", AbCipDataType.Real),  // offset 4
+        ]);
+
+    [Fact]
+    public async Task Two_members_of_same_udt_trigger_one_parent_read()
+    {
+        var (drv, factory) = NewDriver(MotorUdt());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snapshots = await drv.ReadAsync(["Motor.Speed", "Motor.Torque"], CancellationToken.None);
+
+        snapshots.Count.ShouldBe(2);
+        snapshots[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        snapshots[1].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+
+        // Factory should have created ONE runtime (for the parent "Motor") + issued ONE read.
+        // Without the optimization two runtimes (one per member) + two reads would appear.
+        factory.Tags.Count.ShouldBe(1);
+        factory.Tags.ShouldContainKey("Motor");
+        factory.Tags["Motor"].ReadCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Each_member_decodes_at_its_own_offset()
+    {
+        var (drv, factory) = NewDriver(MotorUdt());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        // Arrange the offset-keyed values before the read fires — the planner places
+        // Speed at offset 0 (DInt) and Torque at offset 4 (Real).
+        // The fake records CreationParams so we fetch it up front by the parent name.
+        var snapshotsTask = drv.ReadAsync(["Motor.Speed", "Motor.Torque"], CancellationToken.None);
+        // The factory creates the runtime inside ReadAsync; we need to set the offset map
+        // AFTER creation. Easier path: create the runtime on demand by reading once then
+        // re-arming. Instead: seed via a pre-read by constructing the fake in the factory's
+        // customise hook.
+        var snapshots = await snapshotsTask;
+
+        // First run establishes the runtime + gives the fake a chance to hold its reference.
+        factory.Tags["Motor"].ValuesByOffset[0] = 1234; // Speed
+        factory.Tags["Motor"].ValuesByOffset[4] = 9.5f; // Torque
+
+        snapshots = await drv.ReadAsync(["Motor.Speed", "Motor.Torque"], CancellationToken.None);
+        snapshots[0].Value.ShouldBe(1234);
+        snapshots[1].Value.ShouldBe(9.5f);
+    }
+
+    [Fact]
+    public async Task Parent_read_failure_stamps_every_grouped_member_Bad()
+    {
+        var (drv, factory) = NewDriver(MotorUdt());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        // Prime runtime existence via a first (successful) read so we can flip it to error.
+        await drv.ReadAsync(["Motor.Speed", "Motor.Torque"], CancellationToken.None);
+        factory.Tags["Motor"].Status = -3; // libplctag BadTimeout — mapped in AbCipStatusMapper
+
+        var snapshots = await drv.ReadAsync(["Motor.Speed", "Motor.Torque"], CancellationToken.None);
+
+        snapshots.Count.ShouldBe(2);
+        snapshots[0].StatusCode.ShouldNotBe(AbCipStatusMapper.Good);
+        snapshots[0].Value.ShouldBeNull();
+        snapshots[1].StatusCode.ShouldNotBe(AbCipStatusMapper.Good);
+        snapshots[1].Value.ShouldBeNull();
+    }
+
+    [Fact]
+    public async Task Mixed_batch_groups_udt_and_falls_back_atomics()
+    {
+        var plain = new AbCipTagDefinition("PlainDint", Device, "PlainDint", AbCipDataType.DInt);
+        var (drv, factory) = NewDriver(MotorUdt(), plain);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snapshots = await drv.ReadAsync(
+            ["Motor.Speed", "PlainDint", "Motor.Torque"], CancellationToken.None);
+
+        snapshots.Count.ShouldBe(3);
+        // Motor parent ran one read, PlainDint ran its own read = 2 runtimes, 2 reads total.
+        factory.Tags.Count.ShouldBe(2);
+        factory.Tags.ShouldContainKey("Motor");
+        factory.Tags.ShouldContainKey("PlainDint");
+        factory.Tags["Motor"].ReadCount.ShouldBe(1);
+        factory.Tags["PlainDint"].ReadCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Single_member_of_Udt_uses_per_tag_read_path()
+    {
+        // One member of a UDT doesn't benefit from grouping — the planner demotes to
+        // fallback so the member-level runtime (distinct from the parent runtime) is used,
+        // matching pre-#194 behavior.
+        var (drv, factory) = NewDriver(MotorUdt());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["Motor.Speed"], CancellationToken.None);
+
+        factory.Tags.ShouldContainKey("Motor.Speed");
+        factory.Tags.ShouldNotContainKey("Motor");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipUdtMemberLayoutTests.cs

@@ -0,0 +1,72 @@
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class AbCipUdtMemberLayoutTests
+{
+    [Fact]
+    public void Packed_Atomics_Get_Natural_Alignment_Offsets()
+    {
+        // DInt (4 align) + Real (4) + Int (2) + LInt (8 — forces 2-byte pad before it)
+        var members = new[]
+        {
+            new AbCipStructureMember("A", AbCipDataType.DInt),
+            new AbCipStructureMember("B", AbCipDataType.Real),
+            new AbCipStructureMember("C", AbCipDataType.Int),
+            new AbCipStructureMember("D", AbCipDataType.LInt),
+        };
+
+        var offsets = AbCipUdtMemberLayout.TryBuild(members);
+        offsets.ShouldNotBeNull();
+        offsets!["A"].ShouldBe(0);
+        offsets["B"].ShouldBe(4);
+        offsets["C"].ShouldBe(8);
+        // cursor at 10 after Int; LInt needs 8-byte alignment → pad to 16
+        offsets["D"].ShouldBe(16);
+    }
+
+    [Fact]
+    public void SInt_Packed_Without_Padding()
+    {
+        var members = new[]
+        {
+            new AbCipStructureMember("X", AbCipDataType.SInt),
+            new AbCipStructureMember("Y", AbCipDataType.SInt),
+            new AbCipStructureMember("Z", AbCipDataType.SInt),
+        };
+        var offsets = AbCipUdtMemberLayout.TryBuild(members);
+        offsets!["X"].ShouldBe(0);
+        offsets["Y"].ShouldBe(1);
+        offsets["Z"].ShouldBe(2);
+    }
+
+    [Fact]
+    public void Returns_Null_When_Member_Is_Bool()
+    {
+        // BOOL storage in Logix UDTs is packed into a hidden host byte; declaration-only
+        // layout can't place it. Grouping opts out; per-tag read path handles the member.
+        var members = new[]
+        {
+            new AbCipStructureMember("A", AbCipDataType.DInt),
+            new AbCipStructureMember("Flag", AbCipDataType.Bool),
+        };
+        AbCipUdtMemberLayout.TryBuild(members).ShouldBeNull();
+    }
+
+    [Fact]
+    public void Returns_Null_When_Member_Is_String_Or_Structure()
+    {
+        AbCipUdtMemberLayout.TryBuild(
+            new[] { new AbCipStructureMember("Name", AbCipDataType.String) }).ShouldBeNull();
+        AbCipUdtMemberLayout.TryBuild(
+            new[] { new AbCipStructureMember("Nested", AbCipDataType.Structure) }).ShouldBeNull();
+    }
+
+    [Fact]
+    public void Returns_Null_On_Empty_Members()
+    {
+        AbCipUdtMemberLayout.TryBuild(Array.Empty<AbCipStructureMember>()).ShouldBeNull();
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipUdtReadPlannerTests.cs

@@ -0,0 +1,123 @@
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class AbCipUdtReadPlannerTests
+{
+    private const string Device = "ab://10.0.0.1/1,0";
+
+    [Fact]
+    public void Groups_Two_Members_Of_The_Same_Udt_Parent()
+    {
+        var tags = BuildUdtTagMap(out var _);
+        var plan = AbCipUdtReadPlanner.Build(new[] { "Motor.Speed", "Motor.Torque" }, tags);
+
+        plan.Groups.Count.ShouldBe(1);
+        plan.Groups[0].ParentName.ShouldBe("Motor");
+        plan.Groups[0].Members.Count.ShouldBe(2);
+        plan.Fallbacks.Count.ShouldBe(0);
+    }
+
+    [Fact]
+    public void Single_Member_Reference_Falls_Back_To_Per_Tag_Path()
+    {
+        // Reading just one member of a UDT gains nothing from grouping — one whole-UDT read
+        // vs one member read is equivalent cost but more client-side work. Planner demotes.
+        var tags = BuildUdtTagMap(out var _);
+        var plan = AbCipUdtReadPlanner.Build(new[] { "Motor.Speed" }, tags);
+
+        plan.Groups.ShouldBeEmpty();
+        plan.Fallbacks.Count.ShouldBe(1);
+        plan.Fallbacks[0].Reference.ShouldBe("Motor.Speed");
+    }
+
+    [Fact]
+    public void Unknown_References_Fall_Back_Without_Affecting_Groups()
+    {
+        var tags = BuildUdtTagMap(out var _);
+        var plan = AbCipUdtReadPlanner.Build(
+            new[] { "Motor.Speed", "Motor.Torque", "DoesNotExist", "Motor.NonMember" }, tags);
+
+        plan.Groups.Count.ShouldBe(1);
+        plan.Groups[0].Members.Count.ShouldBe(2);
+        plan.Fallbacks.Count.ShouldBe(2);
+        plan.Fallbacks.ShouldContain(f => f.Reference == "DoesNotExist");
+        plan.Fallbacks.ShouldContain(f => f.Reference == "Motor.NonMember");
+    }
+
+    [Fact]
+    public void Atomic_Top_Level_Tag_Falls_Back_Untouched()
+    {
+        var tags = BuildUdtTagMap(out var _);
+        tags = new Dictionary<string, AbCipTagDefinition>(tags, StringComparer.OrdinalIgnoreCase)
+        {
+            ["PlainDint"] = new("PlainDint", Device, "PlainDint", AbCipDataType.DInt),
+        };
+        var plan = AbCipUdtReadPlanner.Build(new[] { "Motor.Speed", "Motor.Torque", "PlainDint" }, tags);
+
+        plan.Groups.Count.ShouldBe(1);
+        plan.Fallbacks.Count.ShouldBe(1);
+        plan.Fallbacks[0].Reference.ShouldBe("PlainDint");
+    }
+
+    [Fact]
+    public void Udt_With_Bool_Member_Does_Not_Group()
+    {
+        // Any BOOL in the declared members disqualifies the group — offset rules for BOOL
+        // can't be determined from declaration alone (Logix packs them into a hidden host
+        // byte). Fallback path reads each member individually.
+        var members = new[]
+        {
+            new AbCipStructureMember("Run", AbCipDataType.Bool),
+            new AbCipStructureMember("Speed", AbCipDataType.DInt),
+        };
+        var parent = new AbCipTagDefinition("Motor", Device, "Motor", AbCipDataType.Structure,
+            Members: members);
+        var tags = new Dictionary<string, AbCipTagDefinition>(StringComparer.OrdinalIgnoreCase)
+        {
+            ["Motor"] = parent,
+            ["Motor.Run"] = new("Motor.Run", Device, "Motor.Run", AbCipDataType.Bool),
+            ["Motor.Speed"] = new("Motor.Speed", Device, "Motor.Speed", AbCipDataType.DInt),
+        };
+
+        var plan = AbCipUdtReadPlanner.Build(new[] { "Motor.Run", "Motor.Speed" }, tags);
+
+        plan.Groups.ShouldBeEmpty();
+        plan.Fallbacks.Count.ShouldBe(2);
+    }
+
+    [Fact]
+    public void Original_Indices_Preserved_For_Out_Of_Order_Batches()
+    {
+        var tags = BuildUdtTagMap(out var _);
+        var plan = AbCipUdtReadPlanner.Build(
+            new[] { "Other", "Motor.Speed", "DoesNotExist", "Motor.Torque" }, tags);
+
+        // Motor.Speed was at index 1, Motor.Torque at 3 — must survive through the plan so
+        // ReadAsync can write decoded values back at the right output slot.
+        plan.Groups.ShouldHaveSingleItem();
+        var group = plan.Groups[0];
+        group.Members.ShouldContain(m => m.OriginalIndex == 1 && m.Definition.Name == "Motor.Speed");
+        group.Members.ShouldContain(m => m.OriginalIndex == 3 && m.Definition.Name == "Motor.Torque");
+        plan.Fallbacks.ShouldContain(f => f.OriginalIndex == 0 && f.Reference == "Other");
+        plan.Fallbacks.ShouldContain(f => f.OriginalIndex == 2 && f.Reference == "DoesNotExist");
+    }
+
+    private static Dictionary<string, AbCipTagDefinition> BuildUdtTagMap(out AbCipTagDefinition parent)
+    {
+        var members = new[]
+        {
+            new AbCipStructureMember("Speed", AbCipDataType.DInt),
+            new AbCipStructureMember("Torque", AbCipDataType.Real),
+        };
+        parent = new AbCipTagDefinition("Motor", Device, "Motor", AbCipDataType.Structure, Members: members);
+        return new Dictionary<string, AbCipTagDefinition>(StringComparer.OrdinalIgnoreCase)
+        {
+            ["Motor"] = parent,
+            ["Motor.Speed"] = new("Motor.Speed", Device, "Motor.Speed", AbCipDataType.DInt),
+            ["Motor.Torque"] = new("Motor.Torque", Device, "Motor.Torque", AbCipDataType.Real),
+        };
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/FakeAbCipTag.cs

@@ -47,6 +47,21 @@ internal class FakeAbCipTag : IAbCipTagRuntime
 
     public virtual object? DecodeValue(AbCipDataType type, int? bitIndex) => Value;
 
+    /// <summary>
+    ///     Task #194 whole-UDT read support. Tests drive multi-member decoding by setting
+    ///     <see cref="ValuesByOffset"/> — keyed by member byte offset — before invoking
+    ///     <see cref="AbCipDriver.ReadAsync"/>. Falls back to <see cref="Value"/> when the
+    ///     offset is zero or unmapped so existing tests that never set the offset map keep
+    ///     working unchanged.
+    /// </summary>
+    public Dictionary<int, object?> ValuesByOffset { get; } = new();
+
+    public virtual object? DecodeValueAt(AbCipDataType type, int offset, int? bitIndex)
+    {
+        if (ValuesByOffset.TryGetValue(offset, out var v)) return v;
+        return offset == 0 ? Value : null;
+    }
+
     public virtual void EncodeValue(AbCipDataType type, int? bitIndex, object? value) => Value = value;
 
     public virtual void Dispose() => Disposed = true;

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyReadSmokeTests.cs

@@ -0,0 +1,93 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests;
+
+/// <summary>
+///     End-to-end smoke tests against the <c>ab_server</c> PCCC Docker container.
+///     Promotes the AB Legacy driver from unit-only coverage (<c>FakeAbLegacyTag</c>)
+///     to wire-level: real libplctag PCCC stack over real TCP against the ab_server
+///     simulator. Parametrised over all three families (SLC 500 / MicroLogix / PLC-5)
+///     via <c>[AbLegacyTheory]</c> + <c>[MemberData]</c>.
+/// </summary>
+[Collection(AbLegacyServerCollection.Name)]
+[Trait("Category", "Integration")]
+[Trait("Simulator", "ab_server-PCCC")]
+public sealed class AbLegacyReadSmokeTests(AbLegacyServerFixture sim)
+{
+    public static IEnumerable<object[]> Profiles =>
+        KnownProfiles.All.Select(p => new object[] { p });
+
+    [AbLegacyTheory]
+    [MemberData(nameof(Profiles))]
+    public async Task Driver_reads_seeded_N_file_from_ab_server_PCCC(AbLegacyServerProfile profile)
+    {
+        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
+
+        // PCCC PLCs use empty cip-path, but AbLegacyHostAddress still requires the
+        // /cip-path suffix to parse.
+        var deviceUri = $"ab://{sim.Host}:{sim.Port}/";
+        await using var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions(deviceUri, profile.Family)],
+            Tags = [
+                new AbLegacyTagDefinition(
+                    Name: "IntCounter",
+                    DeviceHostAddress: deviceUri,
+                    Address: "N7:0",
+                    DataType: AbLegacyDataType.Int),
+            ],
+            Timeout = TimeSpan.FromSeconds(5),
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, driverInstanceId: $"ablegacy-smoke-{profile.Family}");
+
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        var snapshots = await drv.ReadAsync(
+            ["IntCounter"], TestContext.Current.CancellationToken);
+
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good,
+            $"N7:0 read must succeed against the {profile.Family} compose profile");
+        drv.GetHealth().State.ShouldBe(DriverState.Healthy);
+    }
+
+    [AbLegacyFact]
+    public async Task Slc500_write_then_read_round_trip_on_N7_scratch_register()
+    {
+        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
+
+        // PCCC PLCs use empty cip-path, but AbLegacyHostAddress still requires the
+        // /cip-path suffix to parse.
+        var deviceUri = $"ab://{sim.Host}:{sim.Port}/";
+        await using var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions(deviceUri, AbLegacyPlcFamily.Slc500)],
+            Tags = [
+                new AbLegacyTagDefinition(
+                    Name: "Scratch",
+                    DeviceHostAddress: deviceUri,
+                    Address: "N7:5",
+                    DataType: AbLegacyDataType.Int,
+                    Writable: true),
+            ],
+            Timeout = TimeSpan.FromSeconds(5),
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, driverInstanceId: "ablegacy-smoke-rw");
+
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        const short probe = 0x1234;
+        var writeResults = await drv.WriteAsync(
+            [new WriteRequest("Scratch", probe)],
+            TestContext.Current.CancellationToken);
+        writeResults.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good,
+            "PCCC N7:5 write must succeed end-to-end");
+
+        var readResults = await drv.ReadAsync(
+            ["Scratch"], TestContext.Current.CancellationToken);
+        readResults.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+        Convert.ToInt32(readResults.Single().Value).ShouldBe(probe);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyServerFixture.cs

@@ -0,0 +1,157 @@
+using System.Net.Sockets;
+using Xunit;
+using Xunit.Sdk;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests;
+
+/// <summary>
+///     Reachability probe for the <c>ab_server</c> Docker container running in a PCCC
+///     plc mode (<c>SLC500</c> / <c>Micrologix</c> / <c>PLC/5</c>). Same container image
+///     the AB CIP integration suite uses — libplctag's <c>ab_server</c> supports both
+///     CIP + PCCC families from one binary. Tests skip via
+///     <see cref="AbLegacyFactAttribute"/> / <see cref="AbLegacyTheoryAttribute"/> when
+///     the port isn't live, so <c>dotnet test</c> stays green on a fresh clone without
+///     Docker running.
+/// </summary>
+/// <remarks>
+///     Env-var overrides:
+///     <list type="bullet">
+///       <item><c>AB_LEGACY_ENDPOINT</c> — <c>host:port</c> of the PCCC-mode simulator.
+///         Defaults to <c>localhost:44818</c> (EtherNet/IP port; ab_server's PCCC
+///         emulation exposes PCCC-over-CIP on the same port as CIP itself).</item>
+///     </list>
+///     Distinct from <c>AB_SERVER_ENDPOINT</c> used by the AB CIP fixture so both
+///     can point at different containers simultaneously during a combined test run.
+/// </remarks>
+public sealed class AbLegacyServerFixture : IAsyncLifetime
+{
+    private const string EndpointEnvVar = "AB_LEGACY_ENDPOINT";
+
+    /// <summary>Standard EtherNet/IP port. PCCC-over-CIP rides on the same port as
+    /// native CIP; the differentiator is the <c>--plc</c> flag ab_server was started
+    /// with, not a different TCP listener.</summary>
+    public const int DefaultPort = 44818;
+
+    public string Host { get; } = "127.0.0.1";
+    public int Port { get; } = DefaultPort;
+    public string? SkipReason { get; }
+
+    public AbLegacyServerFixture()
+    {
+        if (Environment.GetEnvironmentVariable(EndpointEnvVar) is { Length: > 0 } raw)
+        {
+            var parts = raw.Split(':', 2);
+            Host = parts[0];
+            if (parts.Length == 2 && int.TryParse(parts[1], out var p)) Port = p;
+        }
+
+        if (!TcpProbe(Host, Port))
+        {
+            SkipReason =
+                $"AB Legacy PCCC simulator at {Host}:{Port} not reachable within 2 s. " +
+                $"Start the Docker container (docker compose -f Docker/docker-compose.yml " +
+                $"--profile slc500 up -d) or override {EndpointEnvVar}.";
+        }
+    }
+
+    public ValueTask InitializeAsync() => ValueTask.CompletedTask;
+    public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+
+    public static bool IsServerAvailable()
+    {
+        var (host, port) = ResolveEndpoint();
+        return TcpProbe(host, port);
+    }
+
+    private static (string Host, int Port) ResolveEndpoint()
+    {
+        var raw = Environment.GetEnvironmentVariable(EndpointEnvVar);
+        if (raw is null) return ("127.0.0.1", DefaultPort);
+        var parts = raw.Split(':', 2);
+        var port = parts.Length == 2 && int.TryParse(parts[1], out var p) ? p : DefaultPort;
+        return (parts[0], port);
+    }
+
+    private static bool TcpProbe(string host, int port)
+    {
+        try
+        {
+            using var client = new TcpClient();
+            var task = client.ConnectAsync(host, port);
+            return task.Wait(TimeSpan.FromSeconds(2)) && client.Connected;
+        }
+        catch { return false; }
+    }
+}
+
+/// <summary>
+///     Per-family marker for the PCCC-mode compose profile a given test targets. The
+///     compose file (<c>Docker/docker-compose.yml</c>) is the canonical source of truth
+///     for which <c>--plc</c> mode + tags each family seeds; this record just ties a
+///     family enum to its compose-profile name + operator-facing notes.
+/// </summary>
+public sealed record AbLegacyServerProfile(
+    AbLegacyPlcFamily Family,
+    string ComposeProfile,
+    string Notes);
+
+/// <summary>Canonical profiles covering every PCCC family the driver supports.</summary>
+public static class KnownProfiles
+{
+    public static readonly AbLegacyServerProfile Slc500 = new(
+        Family: AbLegacyPlcFamily.Slc500,
+        ComposeProfile: "slc500",
+        Notes: "SLC 500 / 5/05 family. ab_server SLC500 mode covers N/F/B/L files.");
+
+    public static readonly AbLegacyServerProfile MicroLogix = new(
+        Family: AbLegacyPlcFamily.MicroLogix,
+        ComposeProfile: "micrologix",
+        Notes: "MicroLogix 1000 / 1100 / 1400. Shares N/F/B file-type coverage with SLC500; ST (ASCII strings) included.");
+
+    public static readonly AbLegacyServerProfile Plc5 = new(
+        Family: AbLegacyPlcFamily.Plc5,
+        ComposeProfile: "plc5",
+        Notes: "PLC-5 family. ab_server PLC/5 mode covers N/F/B; per-family quirks on ST / timer file layouts unit-tested only.");
+
+    public static IReadOnlyList<AbLegacyServerProfile> All { get; } =
+        [Slc500, MicroLogix, Plc5];
+
+    public static AbLegacyServerProfile ForFamily(AbLegacyPlcFamily family) =>
+        All.FirstOrDefault(p => p.Family == family)
+        ?? throw new ArgumentOutOfRangeException(nameof(family), family, "No integration profile for this family.");
+}
+
+[Xunit.CollectionDefinition(Name)]
+public sealed class AbLegacyServerCollection : Xunit.ICollectionFixture<AbLegacyServerFixture>
+{
+    public const string Name = "AbLegacyServer";
+}
+
+/// <summary>
+///     <c>[Fact]</c>-equivalent that skips when the PCCC simulator isn't reachable.
+/// </summary>
+public sealed class AbLegacyFactAttribute : FactAttribute
+{
+    public AbLegacyFactAttribute()
+    {
+        if (!AbLegacyServerFixture.IsServerAvailable())
+            Skip = "AB Legacy PCCC simulator not reachable. Start the Docker container " +
+                   "(docker compose -f Docker/docker-compose.yml --profile slc500 up -d) " +
+                   "or set AB_LEGACY_ENDPOINT.";
+    }
+}
+
+/// <summary>
+///     <c>[Theory]</c>-equivalent with the same gate as <see cref="AbLegacyFactAttribute"/>.
+/// </summary>
+public sealed class AbLegacyTheoryAttribute : TheoryAttribute
+{
+    public AbLegacyTheoryAttribute()
+    {
+        if (!AbLegacyServerFixture.IsServerAvailable())
+            Skip = "AB Legacy PCCC simulator not reachable. Start the Docker container " +
+                   "(docker compose -f Docker/docker-compose.yml --profile slc500 up -d) " +
+                   "or set AB_LEGACY_ENDPOINT.";
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/README.md

@@ -0,0 +1,140 @@
+# AB Legacy PCCC integration-test fixture — `ab_server` (Docker)
+
+[libplctag](https://github.com/libplctag/libplctag)'s `ab_server` supports
+both CIP (ControlLogix / CompactLogix / Micro800) and PCCC (SLC 500 /
+MicroLogix / PLC-5) families from one binary. This fixture reuses the AB
+CIP Docker image (`otopcua-ab-server:libplctag-release`) with different
+`--plc` flags. No new Dockerfile needed — the compose file's `build:`
+block points at the AB CIP `Docker/` folder so `docker compose build`
+from here reuses the same multi-stage build.
+
+**Docker is the only supported launch path**; a fresh clone needs Docker
+Desktop and nothing else.
+
+| File | Purpose |
+|---|---|
+| [`docker-compose.yml`](docker-compose.yml) | Three per-family services (`slc500` / `micrologix` / `plc5`); all bind `:44818` |
+
+## Run
+
+From the repo root:
+
+```powershell
+# SLC 500 family — widest PCCC coverage
+docker compose -f tests\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests\Docker\docker-compose.yml --profile slc500 up
+
+# Per-family
+docker compose -f tests\...\Docker\docker-compose.yml --profile micrologix up
+docker compose -f tests\...\Docker\docker-compose.yml --profile plc5 up
+```
+
+Detached + stop:
+
+```powershell
+docker compose -f tests\...\Docker\docker-compose.yml --profile slc500 up -d
+docker compose -f tests\...\Docker\docker-compose.yml --profile slc500 down
+```
+
+First run builds the `otopcua-ab-server:libplctag-release` image (~3-5
+min — clones libplctag + compiles `ab_server`). If the AB CIP fixture
+already built the image locally, docker reuses the cached layers + this
+runs in seconds. Only one family binds `:44818` at a time; to switch
+families stop the current service + start another.
+
+## Endpoint
+
+- Default: `localhost:44818` (EtherNet/IP standard)
+- Override with `AB_LEGACY_ENDPOINT=host:port` to point at a real SLC /
+  MicroLogix / PLC-5 PLC on its native port.
+
+## Run the integration tests
+
+In a separate shell with a container up:
+
+```powershell
+cd C:\Users\dohertj2\Desktop\lmxopcua
+dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests
+```
+
+`AbLegacyServerFixture` TCP-probes `localhost:44818` at collection init +
+records a skip reason when unreachable. Tests use `[AbLegacyFact]` /
+`[AbLegacyTheory]` which check the same probe.
+
+## What each family seeds
+
+PCCC tag format is `<file>[<size>]` without a type suffix — file letter
+implies type:
+
+- `N` = 16-bit signed integer
+- `F` = 32-bit IEEE 754 float
+- `B` = 1-bit boolean (stored as uint16, bit-addressable via `/n`)
+- `L` = 32-bit signed integer (SLC 5/05 V15+ only)
+- `ST` = 82-byte ASCII string (MicroLogix-specific extension)
+
+| Family | Seeded tags | Notes |
+|---|---|---|
+| SLC 500 | `N7[10]`, `F8[10]`, `B3[10]`, `L19[10]` | Baseline; covers the four numeric file types a typical SLC project uses |
+| MicroLogix | `B3[10]`, `N7[10]`, `L19[10]` | No `F8` — MicroLogix 1000 has no float file; use L19 when scaled integers aren't enough |
+| PLC-5 | `N7[10]`, `F8[10]`, `B3[10]` | No `L` — PLC-5 predates the L file type; DINT equivalents went in integer files |
+
+## Known limitations
+
+### ab_server PCCC read/write round-trip (verified 2026-04-20)
+
+**Scaffold is in place; wire-level round-trip does NOT currently pass
+against `ab_server --plc=SLC500`.** With the SLC500 compose profile up,
+TCP 44818 accepts connections and libplctag negotiates the session,
+but the three smoke tests in `AbLegacyReadSmokeTests.cs` all fail at
+read/write with `BadCommunicationError` (libplctag status `0x80050000`).
+Possible root causes:
+
+- ab_server's PCCC server-side opcode coverage may be narrower than
+  libplctag's PCCC client expects — the tool is primarily a CIP
+  server; PCCC was added later + is noted in libplctag docs as less
+  mature.
+- libplctag's PCCC-over-CIP encapsulation may assume a real SLC 5/05
+  EtherNet/IP NIC's framing that ab_server doesn't emit.
+
+The scaffold ships **as-is** because:
+
+1. The Docker infrastructure + fixture pattern works cleanly (probe
+   passes, container lifecycle is clean, tests skip when absent).
+2. The test classes target the correct shape for what the AB Legacy
+   driver would do against real hardware.
+3. Pointing `AB_LEGACY_ENDPOINT` at a real SLC 5/05 / MicroLogix
+   1100 / 1400 should make the tests pass outright — the failure
+   mode is ab_server-specific, not driver-specific.
+
+Resolution paths (pick one):
+
+1. **File an ab_server bug** in `libplctag/libplctag` to expand PCCC
+   server-side coverage.
+2. **Golden-box tier** via Rockwell RSEmulate 500 — closer to real
+   firmware, but license-gated + RSLinx-dependent.
+3. **Lab rig** — used SLC 5/05 / MicroLogix 1100 on a dedicated
+   network; the authoritative path.
+
+### Other known gaps (unchanged from ab_server)
+
+- **Timer / Counter file decomposition** — PCCC T4 / C5 files contain
+  three-field structs (`.ACC` / `.PRE` / `.DN`). Not in ab_server's
+  scope; tests targeting `T4:0.ACC` stay unit-only.
+- **ST (ASCII string) files** — real MicroLogix ST files have a length
+  field plus CRLF-sensitive semantics that don't round-trip cleanly.
+- **Indirect addressing** (`N7:[N10:5]`) — not in ab_server's scope.
+- **DF1 serial wire behaviour** — the whole ab_server path is TCP;
+  DF1 radio / serial fidelity needs real hardware.
+
+See [`docs/drivers/AbLegacy-Test-Fixture.md`](../../../docs/drivers/AbLegacy-Test-Fixture.md)
+for the full coverage map.
+
+## References
+
+- [libplctag on GitHub](https://github.com/libplctag/libplctag) — `ab_server`
+  lives under `src/tools/ab_server/`
+- [`docs/drivers/AbLegacy-Test-Fixture.md`](../../../docs/drivers/AbLegacy-Test-Fixture.md)
+  — coverage map + gap inventory
+- [`docs/v2/dev-environment.md`](../../../docs/v2/dev-environment.md)
+  §Docker fixtures — full fixture inventory
+- [`../../ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/`](../../ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/)
+  — the shared Dockerfile this compose file's `build:` block references

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/docker-compose.yml

@@ -0,0 +1,74 @@
+# AB Legacy PCCC integration-test fixture — ab_server in PCCC mode.
+#
+# Same image as the AB CIP fixture (otopcua-ab-server:libplctag-release).
+# The build context points at the AB CIP Docker folder one directory over
+# so `docker compose build` from here produces the same image if it
+# doesn't already exist; if it does, docker's cache reuses the layer.
+#
+# One service per PCCC family. All bind :44818 on the host; run one at a
+# time. PCCC tag format differs from CIP: `<file>[<size>]` without a
+# type suffix since the type is implicit in the file letter (N = INT,
+# F = REAL, B = bit-packed, L = DINT).
+#
+# Usage:
+#   docker compose --profile slc500 up
+#   docker compose --profile micrologix up
+#   docker compose --profile plc5 up
+services:
+  slc500:
+    profiles: ["slc500"]
+    build:
+      context: ../../ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker
+      dockerfile: Dockerfile
+    image: otopcua-ab-server:libplctag-release
+    container_name: otopcua-ab-server-slc500
+    restart: "no"
+    ports:
+      - "44818:44818"
+    command: [
+      "ab_server",
+      "--plc=SLC500",
+      "--port=44818",
+      "--tag=N7[10]",
+      "--tag=F8[10]",
+      "--tag=B3[10]",
+      "--tag=L19[10]"
+    ]
+
+  micrologix:
+    profiles: ["micrologix"]
+    image: otopcua-ab-server:libplctag-release
+    build:
+      context: ../../ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker
+      dockerfile: Dockerfile
+    container_name: otopcua-ab-server-micrologix
+    restart: "no"
+    ports:
+      - "44818:44818"
+    command: [
+      "ab_server",
+      "--plc=Micrologix",
+      "--port=44818",
+      "--tag=B3[10]",
+      "--tag=N7[10]",
+      "--tag=L19[10]"
+    ]
+
+  plc5:
+    profiles: ["plc5"]
+    image: otopcua-ab-server:libplctag-release
+    build:
+      context: ../../ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker
+      dockerfile: Dockerfile
+    container_name: otopcua-ab-server-plc5
+    restart: "no"
+    ports:
+      - "44818:44818"
+    command: [
+      "ab_server",
+      "--plc=PLC/5",
+      "--port=44818",
+      "--tag=N7[10]",
+      "--tag=F8[10]",
+      "--tag=B3[10]"
+    ]

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests.csproj

@@ -0,0 +1,35 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="xunit.v3" Version="1.1.0"/>
+        <PackageReference Include="Shouldly" Version="4.3.0"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\src\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <None Update="Docker\**\*" CopyToOutputDirectory="PreserveNewest"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+    </ItemGroup>
+
+</Project>

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests/FwlibFrameHandlerTests.cs

@@ -0,0 +1,200 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using Serilog;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Backend;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests
+{
+    /// <summary>
+    ///     Validates that <see cref="FwlibFrameHandler"/> correctly dispatches each
+    ///     <see cref="FocasMessageKind"/> to the corresponding <see cref="IFocasBackend"/>
+    ///     method and serializes the response into the expected response kind. Uses
+    ///     <see cref="FakeFocasBackend"/> so no hardware is needed.
+    /// </summary>
+    [Trait("Category", "Unit")]
+    public sealed class FwlibFrameHandlerTests
+    {
+        private static async Task RoundTripAsync<TReq, TResp>(
+            IFrameHandler handler, FocasMessageKind reqKind, TReq req, FocasMessageKind expectedRespKind,
+            Action<TResp> assertResponse)
+        {
+            using var buffer = new MemoryStream();
+            using var writer = new FrameWriter(buffer, leaveOpen: true);
+            await handler.HandleAsync(reqKind, MessagePackSerializer.Serialize(req), writer, CancellationToken.None);
+
+            buffer.Position = 0;
+            using var reader = new FrameReader(buffer, leaveOpen: true);
+            var frame = await reader.ReadFrameAsync(CancellationToken.None);
+            frame.HasValue.ShouldBeTrue();
+            frame!.Value.Kind.ShouldBe(expectedRespKind);
+            assertResponse(MessagePackSerializer.Deserialize<TResp>(frame.Value.Body));
+        }
+
+        private static FwlibFrameHandler BuildHandler() =>
+            new(new FakeFocasBackend(), new LoggerConfiguration().CreateLogger());
+
+        [Fact]
+        public async Task OpenSession_returns_a_new_session_id()
+        {
+            long sessionId = 0;
+            await RoundTripAsync<OpenSessionRequest, OpenSessionResponse>(
+                BuildHandler(),
+                FocasMessageKind.OpenSessionRequest,
+                new OpenSessionRequest { HostAddress = "h:8193" },
+                FocasMessageKind.OpenSessionResponse,
+                resp => { resp.Success.ShouldBeTrue(); resp.SessionId.ShouldBeGreaterThan(0L); sessionId = resp.SessionId; });
+            sessionId.ShouldBeGreaterThan(0L);
+        }
+
+        [Fact]
+        public async Task Read_without_open_session_returns_internal_error()
+        {
+            await RoundTripAsync<ReadRequest, ReadResponse>(
+                BuildHandler(),
+                FocasMessageKind.ReadRequest,
+                new ReadRequest
+                {
+                    SessionId = 999,
+                    Address = new FocasAddressDto { Kind = 0, PmcLetter = "R", Number = 100 },
+                    DataType = FocasDataTypeCode.Int32,
+                },
+                FocasMessageKind.ReadResponse,
+                resp => { resp.Success.ShouldBeFalse(); resp.Error.ShouldContain("session-not-open"); });
+        }
+
+        [Fact]
+        public async Task Full_open_write_read_round_trip_preserves_value()
+        {
+            var handler = BuildHandler();
+
+            // Open.
+            using var buffer = new MemoryStream();
+            using var writer = new FrameWriter(buffer, leaveOpen: true);
+            await handler.HandleAsync(FocasMessageKind.OpenSessionRequest,
+                MessagePackSerializer.Serialize(new OpenSessionRequest { HostAddress = "h:8193" }), writer, CancellationToken.None);
+
+            buffer.Position = 0;
+            using var reader = new FrameReader(buffer, leaveOpen: true);
+            var openFrame = await reader.ReadFrameAsync(CancellationToken.None);
+            var openResp = MessagePackSerializer.Deserialize<OpenSessionResponse>(openFrame!.Value.Body);
+            var sessionId = openResp.SessionId;
+
+            // Write 42 at MACRO:500 as Int32.
+            buffer.Position = 0;
+            buffer.SetLength(0);
+            await handler.HandleAsync(FocasMessageKind.WriteRequest,
+                MessagePackSerializer.Serialize(new WriteRequest
+                {
+                    SessionId = sessionId,
+                    Address = new FocasAddressDto { Kind = 2, Number = 500 },
+                    DataType = FocasDataTypeCode.Int32,
+                    ValueTypeCode = FocasDataTypeCode.Int32,
+                    ValueBytes = MessagePackSerializer.Serialize((int)42),
+                }), writer, CancellationToken.None);
+
+            // Read back.
+            buffer.Position = 0;
+            buffer.SetLength(0);
+            await handler.HandleAsync(FocasMessageKind.ReadRequest,
+                MessagePackSerializer.Serialize(new ReadRequest
+                {
+                    SessionId = sessionId,
+                    Address = new FocasAddressDto { Kind = 2, Number = 500 },
+                    DataType = FocasDataTypeCode.Int32,
+                }), writer, CancellationToken.None);
+
+            buffer.Position = 0;
+            var readFrame = await reader.ReadFrameAsync(CancellationToken.None);
+            readFrame.HasValue.ShouldBeTrue();
+            readFrame!.Value.Kind.ShouldBe(FocasMessageKind.ReadResponse);
+            // With buffer reuse there may be multiple queued frames; we want the last one.
+            var lastResp = MessagePackSerializer.Deserialize<ReadResponse>(readFrame.Value.Body);
+            // If the Write frame is first, drain it.
+            if (lastResp.ValueBytes is null)
+            {
+                var next = await reader.ReadFrameAsync(CancellationToken.None);
+                lastResp = MessagePackSerializer.Deserialize<ReadResponse>(next!.Value.Body);
+            }
+            lastResp.Success.ShouldBeTrue();
+            MessagePackSerializer.Deserialize<int>(lastResp.ValueBytes!).ShouldBe(42);
+        }
+
+        [Fact]
+        public async Task PmcBitWrite_sets_specified_bit()
+        {
+            var handler = BuildHandler();
+            using var buffer = new MemoryStream();
+            using var writer = new FrameWriter(buffer, leaveOpen: true);
+
+            await handler.HandleAsync(FocasMessageKind.OpenSessionRequest,
+                MessagePackSerializer.Serialize(new OpenSessionRequest { HostAddress = "h:8193" }), writer, CancellationToken.None);
+            buffer.Position = 0;
+            using var reader = new FrameReader(buffer, leaveOpen: true);
+            var openFrame = await reader.ReadFrameAsync(CancellationToken.None);
+            var sessionId = MessagePackSerializer.Deserialize<OpenSessionResponse>(openFrame!.Value.Body).SessionId;
+
+            buffer.Position = 0; buffer.SetLength(0);
+            await handler.HandleAsync(FocasMessageKind.PmcBitWriteRequest,
+                MessagePackSerializer.Serialize(new PmcBitWriteRequest
+                {
+                    SessionId = sessionId,
+                    Address = new FocasAddressDto { Kind = 0, PmcLetter = "R", Number = 100 },
+                    BitIndex = 3,
+                    Value = true,
+                }), writer, CancellationToken.None);
+
+            buffer.Position = 0;
+            var resp = MessagePackSerializer.Deserialize<PmcBitWriteResponse>(
+                (await reader.ReadFrameAsync(CancellationToken.None))!.Value.Body);
+            resp.Success.ShouldBeTrue();
+            resp.StatusCode.ShouldBe(0u);
+        }
+
+        [Fact]
+        public async Task Probe_reports_healthy_when_session_open()
+        {
+            var handler = BuildHandler();
+            using var buffer = new MemoryStream();
+            using var writer = new FrameWriter(buffer, leaveOpen: true);
+            await handler.HandleAsync(FocasMessageKind.OpenSessionRequest,
+                MessagePackSerializer.Serialize(new OpenSessionRequest { HostAddress = "h:8193" }), writer, CancellationToken.None);
+            buffer.Position = 0;
+            using var reader = new FrameReader(buffer, leaveOpen: true);
+            var sessionId = MessagePackSerializer.Deserialize<OpenSessionResponse>(
+                (await reader.ReadFrameAsync(CancellationToken.None))!.Value.Body).SessionId;
+
+            buffer.Position = 0; buffer.SetLength(0);
+            await handler.HandleAsync(FocasMessageKind.ProbeRequest,
+                MessagePackSerializer.Serialize(new ProbeRequest { SessionId = sessionId }), writer, CancellationToken.None);
+            buffer.Position = 0;
+            var resp = MessagePackSerializer.Deserialize<ProbeResponse>(
+                (await reader.ReadFrameAsync(CancellationToken.None))!.Value.Body);
+            resp.Healthy.ShouldBeTrue();
+        }
+
+        [Fact]
+        public async Task Unconfigured_backend_returns_pointed_error_message()
+        {
+            var handler = new FwlibFrameHandler(new UnconfiguredFocasBackend(), new LoggerConfiguration().CreateLogger());
+            await RoundTripAsync<OpenSessionRequest, OpenSessionResponse>(
+                handler,
+                FocasMessageKind.OpenSessionRequest,
+                new OpenSessionRequest { HostAddress = "h:8193" },
+                FocasMessageKind.OpenSessionResponse,
+                resp =>
+                {
+                    resp.Success.ShouldBeFalse();
+                    resp.Error.ShouldContain("Fwlib32");
+                    resp.ErrorCode.ShouldBe("NoFwlibBackend");
+                });
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests/IpcHandshakeIntegrationTests.cs

@@ -0,0 +1,157 @@
+using System;
+using System.IO;
+using System.IO.Pipes;
+using System.Security.Principal;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using Serilog;
+using Serilog.Core;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Ipc;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests
+{
+    /// <summary>
+    ///     Direct FOCAS Host IPC handshake test. Drives <see cref="PipeServer"/> through a
+    ///     hand-rolled pipe client built on <see cref="FrameReader"/> / <see cref="FrameWriter"/>
+    ///     from FOCAS.Shared. Skipped on Administrator shells because <c>PipeAcl</c> denies
+    ///     the BuiltinAdministrators group.
+    /// </summary>
+    [Trait("Category", "Integration")]
+    public sealed class IpcHandshakeIntegrationTests
+    {
+        private static bool IsAdministrator()
+        {
+            using var identity = WindowsIdentity.GetCurrent();
+            return new WindowsPrincipal(identity).IsInRole(WindowsBuiltInRole.Administrator);
+        }
+
+        private static async Task<(NamedPipeClientStream Stream, FrameReader Reader, FrameWriter Writer)>
+            ConnectAndHelloAsync(string pipeName, string secret, CancellationToken ct)
+        {
+            var stream = new NamedPipeClientStream(".", pipeName, PipeDirection.InOut, PipeOptions.Asynchronous);
+            await stream.ConnectAsync(5_000, ct);
+
+            var reader = new FrameReader(stream, leaveOpen: true);
+            var writer = new FrameWriter(stream, leaveOpen: true);
+            await writer.WriteAsync(FocasMessageKind.Hello,
+                new Hello { PeerName = "test-client", SharedSecret = secret }, ct);
+
+            var ack = await reader.ReadFrameAsync(ct);
+            if (ack is null) throw new EndOfStreamException("no HelloAck");
+            if (ack.Value.Kind != FocasMessageKind.HelloAck)
+                throw new InvalidOperationException("unexpected first frame kind " + ack.Value.Kind);
+            var ackMsg = MessagePackSerializer.Deserialize<HelloAck>(ack.Value.Body);
+            if (!ackMsg.Accepted) throw new UnauthorizedAccessException(ackMsg.RejectReason);
+
+            return (stream, reader, writer);
+        }
+
+        [Fact]
+        public async Task Handshake_with_correct_secret_succeeds_and_heartbeat_round_trips()
+        {
+            if (IsAdministrator()) return;
+
+            using var identity = WindowsIdentity.GetCurrent();
+            var sid = identity.User!;
+            var pipe = $"OtOpcUaFocasTest-{Guid.NewGuid():N}";
+            const string secret = "test-secret-2026";
+            Logger log = new LoggerConfiguration().CreateLogger();
+            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
+
+            var server = new PipeServer(pipe, sid, secret, log);
+            var serverTask = Task.Run(() => server.RunOneConnectionAsync(new StubFrameHandler(), cts.Token));
+
+            var (stream, reader, writer) = await ConnectAndHelloAsync(pipe, secret, cts.Token);
+            using (stream)
+            using (reader)
+            using (writer)
+            {
+                await writer.WriteAsync(FocasMessageKind.Heartbeat,
+                    new Heartbeat { MonotonicTicks = 42 }, cts.Token);
+
+                var hbAck = await reader.ReadFrameAsync(cts.Token);
+                hbAck.HasValue.ShouldBeTrue();
+                hbAck!.Value.Kind.ShouldBe(FocasMessageKind.HeartbeatAck);
+                MessagePackSerializer.Deserialize<HeartbeatAck>(hbAck.Value.Body).MonotonicTicks.ShouldBe(42L);
+            }
+
+            cts.Cancel();
+            try { await serverTask; } catch { }
+            server.Dispose();
+        }
+
+        [Fact]
+        public async Task Handshake_with_wrong_secret_is_rejected()
+        {
+            if (IsAdministrator()) return;
+
+            using var identity = WindowsIdentity.GetCurrent();
+            var sid = identity.User!;
+            var pipe = $"OtOpcUaFocasTest-{Guid.NewGuid():N}";
+            Logger log = new LoggerConfiguration().CreateLogger();
+            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
+
+            var server = new PipeServer(pipe, sid, "real-secret", log);
+            var serverTask = Task.Run(() => server.RunOneConnectionAsync(new StubFrameHandler(), cts.Token));
+
+            await Should.ThrowAsync<UnauthorizedAccessException>(async () =>
+            {
+                var (s, r, w) = await ConnectAndHelloAsync(pipe, "wrong-secret", cts.Token);
+                s.Dispose();
+                r.Dispose();
+                w.Dispose();
+            });
+
+            cts.Cancel();
+            try { await serverTask; } catch { }
+            server.Dispose();
+        }
+
+        [Fact]
+        public async Task Stub_handler_returns_not_implemented_for_data_plane_request()
+        {
+            if (IsAdministrator()) return;
+
+            using var identity = WindowsIdentity.GetCurrent();
+            var sid = identity.User!;
+            var pipe = $"OtOpcUaFocasTest-{Guid.NewGuid():N}";
+            const string secret = "stub-test";
+            Logger log = new LoggerConfiguration().CreateLogger();
+            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
+
+            var server = new PipeServer(pipe, sid, secret, log);
+            var serverTask = Task.Run(() => server.RunOneConnectionAsync(new StubFrameHandler(), cts.Token));
+
+            var (stream, reader, writer) = await ConnectAndHelloAsync(pipe, secret, cts.Token);
+            using (stream)
+            using (reader)
+            using (writer)
+            {
+                await writer.WriteAsync(FocasMessageKind.ReadRequest,
+                    new ReadRequest
+                    {
+                        SessionId = 1,
+                        Address = new FocasAddressDto { Kind = 0, PmcLetter = "R", Number = 100 },
+                        DataType = FocasDataTypeCode.Int32,
+                    },
+                    cts.Token);
+
+                var resp = await reader.ReadFrameAsync(cts.Token);
+                resp.HasValue.ShouldBeTrue();
+                resp!.Value.Kind.ShouldBe(FocasMessageKind.ErrorResponse);
+                var err = MessagePackSerializer.Deserialize<ErrorResponse>(resp.Value.Body);
+                err.Code.ShouldBe("not-implemented");
+                err.Message.ShouldContain("PR C");
+            }
+
+            cts.Cancel();
+            try { await serverTask; } catch { }
+            server.Dispose();
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests.csproj

@@ -0,0 +1,33 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net48</TargetFramework>
+        <PlatformTarget>x86</PlatformTarget>
+        <Prefer32Bit>true</Prefer32Bit>
+        <Nullable>enable</Nullable>
+        <LangVersion>latest</LangVersion>
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.Tests</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="xunit" Version="2.9.2"/>
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+        <PackageReference Include="Shouldly" Version="4.3.0"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\src\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+    </ItemGroup>
+
+</Project>

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests/ContractRoundTripTests.cs

@@ -0,0 +1,280 @@
+using MessagePack;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests;
+
+/// <summary>
+///     MessagePack round-trip coverage for every FOCAS IPC contract. Ensures
+///     <c>[Key]</c>-tagged fields survive serialize -> deserialize without loss so the
+///     wire format stays stable across Proxy (.NET 10) and Host (.NET 4.8) processes.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class ContractRoundTripTests
+{
+    private static T RoundTrip<T>(T value)
+    {
+        var bytes = MessagePackSerializer.Serialize(value);
+        return MessagePackSerializer.Deserialize<T>(bytes);
+    }
+
+    [Fact]
+    public void Hello_round_trips()
+    {
+        var original = new Hello
+        {
+            ProtocolMajor = 1,
+            ProtocolMinor = 2,
+            PeerName = "OtOpcUa.Server",
+            SharedSecret = "abc-123",
+            Features = ["bulk-read", "pmc-rmw"],
+        };
+        var decoded = RoundTrip(original);
+        decoded.ProtocolMajor.ShouldBe(1);
+        decoded.ProtocolMinor.ShouldBe(2);
+        decoded.PeerName.ShouldBe("OtOpcUa.Server");
+        decoded.SharedSecret.ShouldBe("abc-123");
+        decoded.Features.ShouldBe(["bulk-read", "pmc-rmw"]);
+    }
+
+    [Fact]
+    public void HelloAck_rejected_carries_reason()
+    {
+        var original = new HelloAck { Accepted = false, RejectReason = "bad secret" };
+        var decoded = RoundTrip(original);
+        decoded.Accepted.ShouldBeFalse();
+        decoded.RejectReason.ShouldBe("bad secret");
+    }
+
+    [Fact]
+    public void Heartbeat_and_ack_preserve_ticks()
+    {
+        var hb = RoundTrip(new Heartbeat { MonotonicTicks = 987654321 });
+        hb.MonotonicTicks.ShouldBe(987654321);
+
+        var ack = RoundTrip(new HeartbeatAck { MonotonicTicks = 987654321, HostUtcUnixMs = 1_700_000_000_000 });
+        ack.MonotonicTicks.ShouldBe(987654321);
+        ack.HostUtcUnixMs.ShouldBe(1_700_000_000_000);
+    }
+
+    [Fact]
+    public void ErrorResponse_preserves_code_and_message()
+    {
+        var decoded = RoundTrip(new ErrorResponse { Code = "Fwlib32Crashed", Message = "EW_UNEXPECTED" });
+        decoded.Code.ShouldBe("Fwlib32Crashed");
+        decoded.Message.ShouldBe("EW_UNEXPECTED");
+    }
+
+    [Fact]
+    public void OpenSessionRequest_preserves_series_and_timeout()
+    {
+        var decoded = RoundTrip(new OpenSessionRequest
+        {
+            HostAddress = "192.168.1.50:8193",
+            TimeoutMs = 3500,
+            CncSeries = 5,
+        });
+        decoded.HostAddress.ShouldBe("192.168.1.50:8193");
+        decoded.TimeoutMs.ShouldBe(3500);
+        decoded.CncSeries.ShouldBe(5);
+    }
+
+    [Fact]
+    public void OpenSessionResponse_failure_carries_error_code()
+    {
+        var decoded = RoundTrip(new OpenSessionResponse
+        {
+            Success = false,
+            SessionId = 0,
+            Error = "unreachable",
+            ErrorCode = "EW_SOCKET",
+        });
+        decoded.Success.ShouldBeFalse();
+        decoded.Error.ShouldBe("unreachable");
+        decoded.ErrorCode.ShouldBe("EW_SOCKET");
+    }
+
+    [Fact]
+    public void FocasAddressDto_carries_pmc_with_bit_index()
+    {
+        var decoded = RoundTrip(new FocasAddressDto
+        {
+            Kind = 0,
+            PmcLetter = "R",
+            Number = 100,
+            BitIndex = 3,
+        });
+        decoded.Kind.ShouldBe(0);
+        decoded.PmcLetter.ShouldBe("R");
+        decoded.Number.ShouldBe(100);
+        decoded.BitIndex.ShouldBe(3);
+    }
+
+    [Fact]
+    public void FocasAddressDto_macro_omits_letter_and_bit()
+    {
+        var decoded = RoundTrip(new FocasAddressDto { Kind = 2, Number = 500 });
+        decoded.Kind.ShouldBe(2);
+        decoded.PmcLetter.ShouldBeNull();
+        decoded.Number.ShouldBe(500);
+        decoded.BitIndex.ShouldBeNull();
+    }
+
+    [Fact]
+    public void ReadRequest_and_response_round_trip()
+    {
+        var req = RoundTrip(new ReadRequest
+        {
+            SessionId = 42,
+            Address = new FocasAddressDto { Kind = 1, Number = 1815 },
+            DataType = FocasDataTypeCode.Int32,
+            TimeoutMs = 1500,
+        });
+        req.SessionId.ShouldBe(42);
+        req.Address.Number.ShouldBe(1815);
+        req.DataType.ShouldBe(FocasDataTypeCode.Int32);
+
+        var resp = RoundTrip(new ReadResponse
+        {
+            Success = true,
+            StatusCode = 0,
+            ValueBytes = MessagePackSerializer.Serialize((int)12345),
+            ValueTypeCode = FocasDataTypeCode.Int32,
+            SourceTimestampUtcUnixMs = 1_700_000_000_000,
+        });
+        resp.Success.ShouldBeTrue();
+        resp.StatusCode.ShouldBe(0u);
+        MessagePackSerializer.Deserialize<int>(resp.ValueBytes!).ShouldBe(12345);
+        resp.ValueTypeCode.ShouldBe(FocasDataTypeCode.Int32);
+    }
+
+    [Fact]
+    public void WriteRequest_and_response_round_trip()
+    {
+        var req = RoundTrip(new WriteRequest
+        {
+            SessionId = 1,
+            Address = new FocasAddressDto { Kind = 2, Number = 500 },
+            DataType = FocasDataTypeCode.Float64,
+            ValueBytes = MessagePackSerializer.Serialize(3.14159),
+            ValueTypeCode = FocasDataTypeCode.Float64,
+        });
+        MessagePackSerializer.Deserialize<double>(req.ValueBytes!).ShouldBe(3.14159);
+
+        var resp = RoundTrip(new WriteResponse { Success = true, StatusCode = 0 });
+        resp.Success.ShouldBeTrue();
+        resp.StatusCode.ShouldBe(0u);
+    }
+
+    [Fact]
+    public void PmcBitWriteRequest_preserves_bit_and_value()
+    {
+        var req = RoundTrip(new PmcBitWriteRequest
+        {
+            SessionId = 7,
+            Address = new FocasAddressDto { Kind = 0, PmcLetter = "Y", Number = 12 },
+            BitIndex = 5,
+            Value = true,
+        });
+        req.BitIndex.ShouldBe(5);
+        req.Value.ShouldBeTrue();
+    }
+
+    [Fact]
+    public void SubscribeRequest_round_trips_multiple_items()
+    {
+        var original = new SubscribeRequest
+        {
+            SessionId = 1,
+            SubscriptionId = 100,
+            IntervalMs = 250,
+            Items =
+            [
+                new() { MonitoredItemId = 1, Address = new() { Kind = 0, PmcLetter = "R", Number = 100 }, DataType = FocasDataTypeCode.Bit },
+                new() { MonitoredItemId = 2, Address = new() { Kind = 2, Number = 500 }, DataType = FocasDataTypeCode.Float64 },
+            ],
+        };
+        var decoded = RoundTrip(original);
+        decoded.Items.Length.ShouldBe(2);
+        decoded.Items[0].MonitoredItemId.ShouldBe(1);
+        decoded.Items[0].Address.PmcLetter.ShouldBe("R");
+        decoded.Items[1].DataType.ShouldBe(FocasDataTypeCode.Float64);
+    }
+
+    [Fact]
+    public void SubscribeResponse_rejected_items_survive()
+    {
+        var decoded = RoundTrip(new SubscribeResponse
+        {
+            Success = true,
+            RejectedMonitoredItemIds = [2, 7],
+        });
+        decoded.RejectedMonitoredItemIds.ShouldBe([2, 7]);
+    }
+
+    [Fact]
+    public void UnsubscribeRequest_round_trips()
+    {
+        var decoded = RoundTrip(new UnsubscribeRequest { SubscriptionId = 42 });
+        decoded.SubscriptionId.ShouldBe(42);
+    }
+
+    [Fact]
+    public void OnDataChangeNotification_round_trips()
+    {
+        var original = new OnDataChangeNotification
+        {
+            SubscriptionId = 100,
+            Changes =
+            [
+                new()
+                {
+                    MonitoredItemId = 1,
+                    StatusCode = 0,
+                    ValueBytes = MessagePackSerializer.Serialize(true),
+                    ValueTypeCode = FocasDataTypeCode.Bit,
+                    SourceTimestampUtcUnixMs = 1_700_000_000_000,
+                },
+            ],
+        };
+        var decoded = RoundTrip(original);
+        decoded.Changes.Length.ShouldBe(1);
+        MessagePackSerializer.Deserialize<bool>(decoded.Changes[0].ValueBytes!).ShouldBeTrue();
+    }
+
+    [Fact]
+    public void ProbeRequest_and_response_round_trip()
+    {
+        var req = RoundTrip(new ProbeRequest { SessionId = 1, TimeoutMs = 500 });
+        req.TimeoutMs.ShouldBe(500);
+
+        var resp = RoundTrip(new ProbeResponse { Healthy = true, ObservedAtUtcUnixMs = 1_700_000_000_000 });
+        resp.Healthy.ShouldBeTrue();
+        resp.ObservedAtUtcUnixMs.ShouldBe(1_700_000_000_000);
+    }
+
+    [Fact]
+    public void RuntimeStatusChangeNotification_round_trips()
+    {
+        var decoded = RoundTrip(new RuntimeStatusChangeNotification
+        {
+            SessionId = 5,
+            RuntimeStatus = "Stopped",
+            ObservedAtUtcUnixMs = 1_700_000_000_000,
+        });
+        decoded.RuntimeStatus.ShouldBe("Stopped");
+    }
+
+    [Fact]
+    public void RecycleHostRequest_and_response_round_trip()
+    {
+        var req = RoundTrip(new RecycleHostRequest { Kind = "Hard", Reason = "wedge-detected" });
+        req.Kind.ShouldBe("Hard");
+        req.Reason.ShouldBe("wedge-detected");
+
+        var resp = RoundTrip(new RecycleStatusResponse { Accepted = true, GraceSeconds = 20 });
+        resp.Accepted.ShouldBeTrue();
+        resp.GraceSeconds.ShouldBe(20);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests/FramingTests.cs

@@ -0,0 +1,107 @@
+using System.IO;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class FramingTests
+{
+    [Fact]
+    public async Task FrameWriter_round_trips_single_frame_through_FrameReader()
+    {
+        var buffer = new MemoryStream();
+        using (var writer = new FrameWriter(buffer, leaveOpen: true))
+        {
+            await writer.WriteAsync(FocasMessageKind.Hello,
+                new Hello { PeerName = "proxy", SharedSecret = "s3cr3t" }, TestContext.Current.CancellationToken);
+        }
+
+        buffer.Position = 0;
+        using var reader = new FrameReader(buffer, leaveOpen: true);
+        var frame = await reader.ReadFrameAsync(TestContext.Current.CancellationToken);
+        frame.ShouldNotBeNull();
+        frame!.Value.Kind.ShouldBe(FocasMessageKind.Hello);
+        var hello = FrameReader.Deserialize<Hello>(frame.Value.Body);
+        hello.PeerName.ShouldBe("proxy");
+        hello.SharedSecret.ShouldBe("s3cr3t");
+    }
+
+    [Fact]
+    public async Task FrameReader_returns_null_on_clean_EOF_at_frame_boundary()
+    {
+        using var empty = new MemoryStream();
+        using var reader = new FrameReader(empty, leaveOpen: true);
+        var frame = await reader.ReadFrameAsync(TestContext.Current.CancellationToken);
+        frame.ShouldBeNull();
+    }
+
+    [Fact]
+    public async Task FrameReader_throws_on_oversized_length_prefix()
+    {
+        var hostile = new byte[] { 0x7F, 0xFF, 0xFF, 0xFF, 0x01 }; // length > 16 MiB
+        using var stream = new MemoryStream(hostile);
+        using var reader = new FrameReader(stream, leaveOpen: true);
+        await Should.ThrowAsync<InvalidDataException>(async () =>
+            await reader.ReadFrameAsync(TestContext.Current.CancellationToken));
+    }
+
+    [Fact]
+    public async Task FrameReader_throws_on_mid_frame_eof()
+    {
+        var buffer = new MemoryStream();
+        using (var writer = new FrameWriter(buffer, leaveOpen: true))
+        {
+            await writer.WriteAsync(FocasMessageKind.Hello, new Hello { PeerName = "x" },
+                TestContext.Current.CancellationToken);
+        }
+        // Truncate so body is incomplete.
+        var truncated = buffer.ToArray()[..(buffer.ToArray().Length - 2)];
+        using var partial = new MemoryStream(truncated);
+        using var reader = new FrameReader(partial, leaveOpen: true);
+        await Should.ThrowAsync<EndOfStreamException>(async () =>
+            await reader.ReadFrameAsync(TestContext.Current.CancellationToken));
+    }
+
+    [Fact]
+    public async Task FrameWriter_serializes_concurrent_writes()
+    {
+        var buffer = new MemoryStream();
+        using var writer = new FrameWriter(buffer, leaveOpen: true);
+
+        var tasks = Enumerable.Range(0, 20).Select(i => writer.WriteAsync(
+            FocasMessageKind.Heartbeat,
+            new Heartbeat { MonotonicTicks = i },
+            TestContext.Current.CancellationToken)).ToArray();
+        await Task.WhenAll(tasks);
+
+        buffer.Position = 0;
+        using var reader = new FrameReader(buffer, leaveOpen: true);
+        var seen = new List<long>();
+        while (await reader.ReadFrameAsync(TestContext.Current.CancellationToken) is { } frame)
+        {
+            frame.Kind.ShouldBe(FocasMessageKind.Heartbeat);
+            seen.Add(FrameReader.Deserialize<Heartbeat>(frame.Body).MonotonicTicks);
+        }
+        seen.Count.ShouldBe(20);
+        seen.OrderBy(x => x).ShouldBe(Enumerable.Range(0, 20).Select(x => (long)x));
+    }
+
+    [Fact]
+    public void MessageKind_values_are_stable()
+    {
+        // Guardrail — if someone reorders/renumbers, the wire format breaks for deployed peers.
+        ((byte)FocasMessageKind.Hello).ShouldBe((byte)0x01);
+        ((byte)FocasMessageKind.Heartbeat).ShouldBe((byte)0x03);
+        ((byte)FocasMessageKind.OpenSessionRequest).ShouldBe((byte)0x10);
+        ((byte)FocasMessageKind.ReadRequest).ShouldBe((byte)0x30);
+        ((byte)FocasMessageKind.WriteRequest).ShouldBe((byte)0x32);
+        ((byte)FocasMessageKind.PmcBitWriteRequest).ShouldBe((byte)0x34);
+        ((byte)FocasMessageKind.SubscribeRequest).ShouldBe((byte)0x40);
+        ((byte)FocasMessageKind.OnDataChangeNotification).ShouldBe((byte)0x43);
+        ((byte)FocasMessageKind.ProbeRequest).ShouldBe((byte)0x70);
+        ((byte)FocasMessageKind.ErrorResponse).ShouldBe((byte)0xFE);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests.csproj

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Tests</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="xunit.v3" Version="1.1.0"/>
+        <PackageReference Include="Shouldly" Version="4.3.0"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\src\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+    </ItemGroup>
+
+</Project>

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasCapabilityMatrixTests.cs

@@ -0,0 +1,156 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+/// <summary>
+///     Version-matrix coverage for <see cref="FocasCapabilityMatrix"/>. Encodes the
+///     documented Fanuc FOCAS Developer Kit support boundaries per CNC series so a
+///     config-time change that widens or narrows a range without updating
+///     <c>docs/v2/focas-version-matrix.md</c> fails a test. Every assertion cites the
+///     specific matrix row it reflects.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class FocasCapabilityMatrixTests
+{
+    // ---- Macro ranges ----
+
+    [Theory]
+    [InlineData(FocasCncSeries.Sixteen_i,     999,   true)]
+    [InlineData(FocasCncSeries.Sixteen_i,     1000,  false)]  // above legacy ceiling
+    [InlineData(FocasCncSeries.Zero_i_D,      999,   true)]
+    [InlineData(FocasCncSeries.Zero_i_D,      9999,  false)]  // 0i-D is still legacy-ceiling
+    [InlineData(FocasCncSeries.Zero_i_F,      9999,  true)]   // widened on 0i-F
+    [InlineData(FocasCncSeries.Zero_i_F,      10000, false)]
+    [InlineData(FocasCncSeries.Thirty_i,      99999, true)]   // highest-end
+    [InlineData(FocasCncSeries.Thirty_i,      100000, false)]
+    [InlineData(FocasCncSeries.PowerMotion_i, 999,   true)]
+    [InlineData(FocasCncSeries.PowerMotion_i, 1000,  false)]  // atypical coverage
+    public void Macro_range_matches_series(FocasCncSeries series, int number, bool accepted)
+    {
+        var address = new FocasAddress(FocasAreaKind.Macro, null, number, null);
+        var result = FocasCapabilityMatrix.Validate(series, address);
+        (result is null).ShouldBe(accepted,
+            $"Macro #{number} on {series}: expected {(accepted ? "accept" : "reject")}, got {(result ?? "accept")}");
+    }
+
+    // ---- Parameter ranges ----
+
+    [Theory]
+    [InlineData(FocasCncSeries.Sixteen_i, 9999,  true)]
+    [InlineData(FocasCncSeries.Sixteen_i, 10000, false)]  // 16i capped at 9999
+    [InlineData(FocasCncSeries.Zero_i_F,  14999, true)]
+    [InlineData(FocasCncSeries.Zero_i_F,  15000, false)]
+    [InlineData(FocasCncSeries.Thirty_i,  29999, true)]
+    [InlineData(FocasCncSeries.Thirty_i,  30000, false)]
+    public void Parameter_range_matches_series(FocasCncSeries series, int number, bool accepted)
+    {
+        var address = new FocasAddress(FocasAreaKind.Parameter, null, number, null);
+        var result = FocasCapabilityMatrix.Validate(series, address);
+        (result is null).ShouldBe(accepted);
+    }
+
+    // ---- PMC letters ----
+
+    [Theory]
+    [InlineData(FocasCncSeries.Sixteen_i,  "X", true)]
+    [InlineData(FocasCncSeries.Sixteen_i,  "Y", true)]
+    [InlineData(FocasCncSeries.Sixteen_i,  "R", true)]
+    [InlineData(FocasCncSeries.Sixteen_i,  "F", false)]  // 16i has no F/G signal groups
+    [InlineData(FocasCncSeries.Sixteen_i,  "G", false)]
+    [InlineData(FocasCncSeries.Sixteen_i,  "K", false)]
+    [InlineData(FocasCncSeries.Zero_i_D,   "E", true)]   // widened since 0i-D
+    [InlineData(FocasCncSeries.Zero_i_D,   "F", false)]  // still no F on 0i-D
+    [InlineData(FocasCncSeries.Zero_i_F,   "F", true)]   // F/G added on 0i-F
+    [InlineData(FocasCncSeries.Zero_i_F,   "K", false)]  // K/T still 30i-only
+    [InlineData(FocasCncSeries.Thirty_i,   "K", true)]
+    [InlineData(FocasCncSeries.Thirty_i,   "T", true)]
+    [InlineData(FocasCncSeries.Thirty_i,   "Q", false)]  // unsupported even on 30i
+    public void Pmc_letter_matches_series(FocasCncSeries series, string letter, bool accepted)
+    {
+        var address = new FocasAddress(FocasAreaKind.Pmc, letter, 0, null);
+        var result = FocasCapabilityMatrix.Validate(series, address);
+        (result is null).ShouldBe(accepted,
+            $"PMC letter '{letter}' on {series}: expected {(accepted ? "accept" : "reject")}, got {(result ?? "accept")}");
+    }
+
+    // ---- PMC number ceiling ----
+
+    [Theory]
+    [InlineData(FocasCncSeries.Sixteen_i,  "R", 999,  true)]
+    [InlineData(FocasCncSeries.Sixteen_i,  "R", 1000, false)]
+    [InlineData(FocasCncSeries.Zero_i_D,   "R", 1999, true)]
+    [InlineData(FocasCncSeries.Zero_i_D,   "R", 2000, false)]
+    [InlineData(FocasCncSeries.Zero_i_F,   "R", 9999, true)]
+    [InlineData(FocasCncSeries.Zero_i_F,   "R", 10000, false)]
+    [InlineData(FocasCncSeries.Thirty_i,   "R", 59999, true)]
+    [InlineData(FocasCncSeries.Thirty_i,   "R", 60000, false)]
+    public void Pmc_number_ceiling_matches_series(FocasCncSeries series, string letter, int number, bool accepted)
+    {
+        var address = new FocasAddress(FocasAreaKind.Pmc, letter, number, null);
+        var result = FocasCapabilityMatrix.Validate(series, address);
+        (result is null).ShouldBe(accepted);
+    }
+
+    // ---- Unknown series is permissive ----
+
+    [Theory]
+    [InlineData("Z", 999_999)]   // absurd PMC address
+    [InlineData("Q", 0)]         // non-existent letter
+    public void Unknown_series_accepts_any_PMC(string letter, int number)
+    {
+        var address = new FocasAddress(FocasAreaKind.Pmc, letter, number, null);
+        FocasCapabilityMatrix.Validate(FocasCncSeries.Unknown, address).ShouldBeNull();
+    }
+
+    [Fact]
+    public void Unknown_series_accepts_any_macro_number()
+    {
+        var address = new FocasAddress(FocasAreaKind.Macro, null, 999_999, null);
+        FocasCapabilityMatrix.Validate(FocasCncSeries.Unknown, address).ShouldBeNull();
+    }
+
+    [Fact]
+    public void Unknown_series_accepts_any_parameter_number()
+    {
+        var address = new FocasAddress(FocasAreaKind.Parameter, null, 999_999, null);
+        FocasCapabilityMatrix.Validate(FocasCncSeries.Unknown, address).ShouldBeNull();
+    }
+
+    // ---- Reason messages include enough context to diagnose ----
+
+    [Fact]
+    public void Rejection_message_names_series_and_limit()
+    {
+        var address = new FocasAddress(FocasAreaKind.Macro, null, 100_000, null);
+        var reason = FocasCapabilityMatrix.Validate(FocasCncSeries.Zero_i_F, address);
+        reason.ShouldNotBeNull();
+        reason.ShouldContain("100000");
+        reason.ShouldContain("Zero_i_F");
+        reason.ShouldContain("9999");
+    }
+
+    [Fact]
+    public void Pmc_rejection_lists_accepted_letters()
+    {
+        var address = new FocasAddress(FocasAreaKind.Pmc, "Q", 0, null);
+        var reason = FocasCapabilityMatrix.Validate(FocasCncSeries.Thirty_i, address);
+        reason.ShouldNotBeNull();
+        reason.ShouldContain("'Q'");
+        reason.ShouldContain("X");  // some accepted letter should appear
+        reason.ShouldContain("Y");
+    }
+
+    // ---- PMC address letter is case-insensitive ----
+
+    [Theory]
+    [InlineData("x")]
+    [InlineData("X")]
+    [InlineData("f")]
+    public void Pmc_letter_match_is_case_insensitive_on_30i(string letter)
+    {
+        var address = new FocasAddress(FocasAreaKind.Pmc, letter, 0, null);
+        FocasCapabilityMatrix.Validate(FocasCncSeries.Thirty_i, address).ShouldBeNull();
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/IpcFocasClientTests.cs

@@ -0,0 +1,265 @@
+using MessagePack;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Ipc;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+/// <summary>
+///     End-to-end IPC round-trips over an in-memory loopback: <c>IpcFocasClient</c> talks
+///     to a test fake that plays the Host's role by reading frames, dispatching on kind,
+///     and responding with canned DTOs. Validates that every <see cref="IFocasClient"/>
+///     method translates to the right wire frame + decodes the response correctly.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class IpcFocasClientTests
+{
+    private const string Secret = "test-secret";
+
+    private static async Task ServerLoopAsync(Stream serverSide, Func<FocasMessageKind, byte[], FrameWriter, Task> dispatch, CancellationToken ct)
+    {
+        using var reader = new FrameReader(serverSide, leaveOpen: true);
+        using var writer = new FrameWriter(serverSide, leaveOpen: true);
+
+        // Hello handshake.
+        var first = await reader.ReadFrameAsync(ct);
+        if (first is null) return;
+        var hello = MessagePackSerializer.Deserialize<Hello>(first.Value.Body);
+        var accepted = hello.SharedSecret == Secret;
+        await writer.WriteAsync(FocasMessageKind.HelloAck,
+            new HelloAck { Accepted = accepted, RejectReason = accepted ? null : "wrong-secret" }, ct);
+        if (!accepted) return;
+
+        while (!ct.IsCancellationRequested)
+        {
+            var frame = await reader.ReadFrameAsync(ct);
+            if (frame is null) return;
+            await dispatch(frame.Value.Kind, frame.Value.Body, writer);
+        }
+    }
+
+    [Fact]
+    public async Task Connect_sends_OpenSessionRequest_and_caches_session_id()
+    {
+        await using var loop = new IpcLoopback();
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+
+        OpenSessionRequest? received = null;
+        var server = Task.Run(() => ServerLoopAsync(loop.ServerSide, async (kind, body, writer) =>
+        {
+            if (kind == FocasMessageKind.OpenSessionRequest)
+            {
+                received = MessagePackSerializer.Deserialize<OpenSessionRequest>(body);
+                await writer.WriteAsync(FocasMessageKind.OpenSessionResponse,
+                    new OpenSessionResponse { Success = true, SessionId = 42 }, cts.Token);
+            }
+        }, cts.Token));
+
+        var ipc = await FocasIpcClient.ConnectAsync(loop.ClientSide, Secret, cts.Token);
+        var client = new IpcFocasClient(ipc, FocasCncSeries.Thirty_i);
+        await client.ConnectAsync(new FocasHostAddress("192.168.1.50", 8193), TimeSpan.FromSeconds(2), cts.Token);
+
+        client.IsConnected.ShouldBeTrue();
+        received.ShouldNotBeNull();
+        received!.HostAddress.ShouldBe("192.168.1.50:8193");
+        received.CncSeries.ShouldBe((int)FocasCncSeries.Thirty_i);
+
+        cts.Cancel();
+        try { await server; } catch { }
+    }
+
+    [Fact]
+    public async Task Connect_throws_when_host_rejects()
+    {
+        await using var loop = new IpcLoopback();
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+
+        var server = Task.Run(() => ServerLoopAsync(loop.ServerSide, async (kind, body, writer) =>
+        {
+            if (kind == FocasMessageKind.OpenSessionRequest)
+            {
+                await writer.WriteAsync(FocasMessageKind.OpenSessionResponse,
+                    new OpenSessionResponse { Success = false, Error = "unreachable", ErrorCode = "EW_SOCKET" }, cts.Token);
+            }
+        }, cts.Token));
+
+        var ipc = await FocasIpcClient.ConnectAsync(loop.ClientSide, Secret, cts.Token);
+        var client = new IpcFocasClient(ipc);
+        await Should.ThrowAsync<InvalidOperationException>(async () =>
+            await client.ConnectAsync(new FocasHostAddress("10.0.0.1", 8193), TimeSpan.FromSeconds(1), cts.Token));
+
+        cts.Cancel();
+        try { await server; } catch { }
+    }
+
+    [Fact]
+    public async Task Read_sends_ReadRequest_and_decodes_response()
+    {
+        await using var loop = new IpcLoopback();
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+
+        ReadRequest? received = null;
+        var server = Task.Run(() => ServerLoopAsync(loop.ServerSide, async (kind, body, writer) =>
+        {
+            switch (kind)
+            {
+                case FocasMessageKind.OpenSessionRequest:
+                    await writer.WriteAsync(FocasMessageKind.OpenSessionResponse,
+                        new OpenSessionResponse { Success = true, SessionId = 1 }, cts.Token);
+                    break;
+                case FocasMessageKind.ReadRequest:
+                    received = MessagePackSerializer.Deserialize<ReadRequest>(body);
+                    await writer.WriteAsync(FocasMessageKind.ReadResponse,
+                        new ReadResponse
+                        {
+                            Success = true,
+                            StatusCode = 0,
+                            ValueBytes = MessagePackSerializer.Serialize((int)12345),
+                            ValueTypeCode = FocasDataTypeCode.Int32,
+                        }, cts.Token);
+                    break;
+            }
+        }, cts.Token));
+
+        var ipc = await FocasIpcClient.ConnectAsync(loop.ClientSide, Secret, cts.Token);
+        var client = new IpcFocasClient(ipc);
+        await client.ConnectAsync(new FocasHostAddress("h", 8193), TimeSpan.FromSeconds(1), cts.Token);
+
+        var addr = new FocasAddress(FocasAreaKind.Parameter, null, 1815, null);
+        var (value, status) = await client.ReadAsync(addr, FocasDataType.Int32, cts.Token);
+        status.ShouldBe(0u);
+        value.ShouldBe(12345);
+        received!.Address.Number.ShouldBe(1815);
+
+        cts.Cancel();
+        try { await server; } catch { }
+    }
+
+    [Fact]
+    public async Task Write_sends_WriteRequest_and_returns_status()
+    {
+        await using var loop = new IpcLoopback();
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+
+        var server = Task.Run(() => ServerLoopAsync(loop.ServerSide, async (kind, body, writer) =>
+        {
+            switch (kind)
+            {
+                case FocasMessageKind.OpenSessionRequest:
+                    await writer.WriteAsync(FocasMessageKind.OpenSessionResponse,
+                        new OpenSessionResponse { Success = true, SessionId = 1 }, cts.Token);
+                    break;
+                case FocasMessageKind.WriteRequest:
+                    var req = MessagePackSerializer.Deserialize<WriteRequest>(body);
+                    MessagePackSerializer.Deserialize<double>(req.ValueBytes!).ShouldBe(3.14);
+                    await writer.WriteAsync(FocasMessageKind.WriteResponse,
+                        new WriteResponse { Success = true, StatusCode = 0 }, cts.Token);
+                    break;
+            }
+        }, cts.Token));
+
+        var ipc = await FocasIpcClient.ConnectAsync(loop.ClientSide, Secret, cts.Token);
+        var client = new IpcFocasClient(ipc);
+        await client.ConnectAsync(new FocasHostAddress("h", 8193), TimeSpan.FromSeconds(1), cts.Token);
+
+        var status = await client.WriteAsync(new FocasAddress(FocasAreaKind.Macro, null, 500, null),
+            FocasDataType.Float64, 3.14, cts.Token);
+        status.ShouldBe(0u);
+
+        cts.Cancel();
+        try { await server; } catch { }
+    }
+
+    [Fact]
+    public async Task Write_pmc_bit_sends_first_class_RMW_frame()
+    {
+        await using var loop = new IpcLoopback();
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+
+        PmcBitWriteRequest? received = null;
+        var server = Task.Run(() => ServerLoopAsync(loop.ServerSide, async (kind, body, writer) =>
+        {
+            switch (kind)
+            {
+                case FocasMessageKind.OpenSessionRequest:
+                    await writer.WriteAsync(FocasMessageKind.OpenSessionResponse,
+                        new OpenSessionResponse { Success = true, SessionId = 1 }, cts.Token);
+                    break;
+                case FocasMessageKind.PmcBitWriteRequest:
+                    received = MessagePackSerializer.Deserialize<PmcBitWriteRequest>(body);
+                    await writer.WriteAsync(FocasMessageKind.PmcBitWriteResponse,
+                        new PmcBitWriteResponse { Success = true, StatusCode = 0 }, cts.Token);
+                    break;
+            }
+        }, cts.Token));
+
+        var ipc = await FocasIpcClient.ConnectAsync(loop.ClientSide, Secret, cts.Token);
+        var client = new IpcFocasClient(ipc);
+        await client.ConnectAsync(new FocasHostAddress("h", 8193), TimeSpan.FromSeconds(1), cts.Token);
+
+        var addr = new FocasAddress(FocasAreaKind.Pmc, "R", 100, BitIndex: 5);
+        var status = await client.WriteAsync(addr, FocasDataType.Bit, true, cts.Token);
+        status.ShouldBe(0u);
+        received.ShouldNotBeNull();
+        received!.BitIndex.ShouldBe(5);
+        received.Value.ShouldBeTrue();
+        received.Address.PmcLetter.ShouldBe("R");
+
+        cts.Cancel();
+        try { await server; } catch { }
+    }
+
+    [Fact]
+    public async Task Probe_round_trips_health_from_host()
+    {
+        await using var loop = new IpcLoopback();
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+
+        var server = Task.Run(() => ServerLoopAsync(loop.ServerSide, async (kind, body, writer) =>
+        {
+            switch (kind)
+            {
+                case FocasMessageKind.OpenSessionRequest:
+                    await writer.WriteAsync(FocasMessageKind.OpenSessionResponse,
+                        new OpenSessionResponse { Success = true, SessionId = 1 }, cts.Token);
+                    break;
+                case FocasMessageKind.ProbeRequest:
+                    await writer.WriteAsync(FocasMessageKind.ProbeResponse,
+                        new ProbeResponse { Healthy = true, ObservedAtUtcUnixMs = 1_700_000_000_000 }, cts.Token);
+                    break;
+            }
+        }, cts.Token));
+
+        var ipc = await FocasIpcClient.ConnectAsync(loop.ClientSide, Secret, cts.Token);
+        var client = new IpcFocasClient(ipc);
+        await client.ConnectAsync(new FocasHostAddress("h", 8193), TimeSpan.FromSeconds(1), cts.Token);
+        (await client.ProbeAsync(cts.Token)).ShouldBeTrue();
+
+        cts.Cancel();
+        try { await server; } catch { }
+    }
+
+    [Fact]
+    public async Task Error_response_from_host_surfaces_as_FocasIpcException()
+    {
+        await using var loop = new IpcLoopback();
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+
+        var server = Task.Run(() => ServerLoopAsync(loop.ServerSide, async (kind, body, writer) =>
+        {
+            await writer.WriteAsync(FocasMessageKind.ErrorResponse,
+                new ErrorResponse { Code = "backend-exception", Message = "simulated" }, cts.Token);
+        }, cts.Token));
+
+        var ipc = await FocasIpcClient.ConnectAsync(loop.ClientSide, Secret, cts.Token);
+        var client = new IpcFocasClient(ipc);
+        var ex = await Should.ThrowAsync<FocasIpcException>(async () =>
+            await client.ConnectAsync(new FocasHostAddress("h", 8193), TimeSpan.FromSeconds(1), cts.Token));
+        ex.Code.ShouldBe("backend-exception");
+
+        cts.Cancel();
+        try { await server; } catch { }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/IpcLoopback.cs

@@ -0,0 +1,72 @@
+using System.IO.Pipelines;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+/// <summary>
+///     Bidirectional in-memory stream pair for IPC tests. Two <c>System.IO.Pipelines.Pipe</c>
+///     instances — one per direction — exposed as <see cref="System.IO.Stream"/> endpoints
+///     via <c>PipeReader.AsStream</c> / <c>PipeWriter.AsStream</c>. Lets the test set up a
+///     <c>FocasIpcClient</c> on one end and a minimal fake server loop on the other without
+///     standing up a real named pipe.
+/// </summary>
+internal sealed class IpcLoopback : IAsyncDisposable
+{
+    public Stream ClientSide { get; }
+    public Stream ServerSide { get; }
+
+    public IpcLoopback()
+    {
+        var clientToServer = new Pipe();
+        var serverToClient = new Pipe();
+
+        ClientSide = new DuplexPipeStream(serverToClient.Reader.AsStream(), clientToServer.Writer.AsStream());
+        ServerSide = new DuplexPipeStream(clientToServer.Reader.AsStream(), serverToClient.Writer.AsStream());
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await ClientSide.DisposeAsync();
+        await ServerSide.DisposeAsync();
+    }
+
+    private sealed class DuplexPipeStream(Stream read, Stream write) : Stream
+    {
+        public override bool CanRead => true;
+        public override bool CanWrite => true;
+        public override bool CanSeek => false;
+        public override long Length => throw new NotSupportedException();
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public override int Read(byte[] buffer, int offset, int count) => read.Read(buffer, offset, count);
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken ct) =>
+            read.ReadAsync(buffer, offset, count, ct);
+        public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken ct = default) =>
+            read.ReadAsync(buffer, ct);
+
+        public override void Write(byte[] buffer, int offset, int count) => write.Write(buffer, offset, count);
+        public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken ct) =>
+            write.WriteAsync(buffer, offset, count, ct);
+        public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken ct = default) =>
+            write.WriteAsync(buffer, ct);
+
+        public override void Flush() => write.Flush();
+        public override Task FlushAsync(CancellationToken ct) => write.FlushAsync(ct);
+
+        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
+        public override void SetLength(long value) => throw new NotSupportedException();
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                read.Dispose();
+                write.Dispose();
+            }
+            base.Dispose(disposing);
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/DL205/DL205Profile.cs

@@ -2,7 +2,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests.DL205;
 
 /// <summary>
 ///     Tag map for the AutomationDirect DL205 device class. Mirrors what the pymodbus
-///     <c>dl205.json</c> profile in <c>Pymodbus/dl205.json</c> exposes (or the real PLC, when
+///     <c>dl205.json</c> profile in <c>Docker/profiles/dl205.json</c> exposes (or the real PLC, when
 ///     <see cref="ModbusSimulatorFixture"/> is pointed at one).
 /// </summary>
 /// <remarks>
@@ -16,8 +16,8 @@ public static class DL205Profile
 {
     /// <summary>
     ///     Holding register the smoke test writes + reads. Address 200 is the first cell of the
-    ///     scratch HR range in both <c>Pymodbus/standard.json</c> (HR[200..209] = 0) and
-    ///     <c>Pymodbus/dl205.json</c> (HR[4096..4103] added in PR 43 for the same purpose), so
+    ///     scratch HR range in both <c>Docker/profiles/standard.json</c> (HR[200..209] = 0) and
+    ///     <c>Docker/profiles/dl205.json</c> (HR[4096..4103] added in PR 43 for the same purpose), so
     ///     the smoke test runs identically against either simulator profile. Originally
     ///     targeted HR[100] — moved to HR[200] when the standard profile claimed HR[100] as
     ///     the auto-incrementing register that drives subscribe-and-receive tests.

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/DL205/DL205StringQuirkTests.cs

@@ -12,7 +12,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests.DL205;
 /// </summary>
 /// <remarks>
 ///     <para>
-///         Requires the dl205 profile (<c>Pymodbus\serve.ps1 -Profile dl205</c>). The standard
+///         Requires the dl205 profile (<c>docker compose -f Docker/docker-compose.yml --profile dl205 up</c>). The standard
 ///         profile does not seed HR[1040..1042] with string bytes, so running this against the
 ///         standard profile returns <c>"\0\0\0\0\0"</c> and the test fails. Skip when the env
 ///         var <c>MODBUS_SIM_PROFILE</c> is not set to <c>dl205</c>.

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/Dockerfile

@@ -0,0 +1,27 @@
+# pymodbus simulator container for the Modbus integration suite.
+#
+# Pinned base + package version so the fixture surface is reproducible —
+# matches the version referenced in docs/drivers/Modbus-Test-Fixture.md.
+FROM python:3.12-slim-bookworm
+
+LABEL org.opencontainers.image.source="https://github.com/dohertj2/lmxopcua" \
+      org.opencontainers.image.description="pymodbus simulator for OtOpcUa Modbus driver integration tests"
+
+RUN pip install --no-cache-dir "pymodbus[simulator]==3.13.0"
+
+# Ship every profile in the image so one container can serve whichever
+# family a test run needs; the compose file picks which JSON is active via
+# the command override.
+WORKDIR /fixtures
+COPY profiles/ /fixtures/
+
+EXPOSE 5020
+
+# Default to the standard profile; docker-compose.yml overrides per service.
+# --http_port intentionally omitted; pymodbus 3.13's web UI binds on a
+# container-local default we don't publish, so it's not reachable from the
+# host and costs nothing.
+CMD ["pymodbus.simulator", \
+     "--modbus_server", "srv", \
+     "--modbus_device",  "dev", \
+     "--json_file",      "/fixtures/standard.json"]

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/README.md

@@ -0,0 +1,67 @@
+# Modbus integration-test fixture — pymodbus simulator
+
+The Modbus driver's integration tests talk to a
+[`pymodbus`](https://pymodbus.readthedocs.io/) simulator running as a
+pinned Docker container. One image, per-profile service in compose, same
+port binding (`5020`) regardless of which profile is live. Docker is the
+only supported launch path — a fresh clone needs Docker Desktop and
+nothing else.
+
+| File | Purpose |
+|---|---|
+| [`Dockerfile`](Dockerfile) | `python:3.12-slim-bookworm` + `pymodbus[simulator]==3.13.0` + the four profile JSONs |
+| [`docker-compose.yml`](docker-compose.yml) | One service per profile (`standard` / `dl205` / `mitsubishi` / `s7_1500`); all bind `:5020` so only one runs at a time |
+| [`profiles/*.json`](profiles/) | Same seed-register definitions the native launcher uses — canonical source |
+
+## Run
+
+From the repo root:
+
+```powershell
+# Build + start the standard profile
+docker compose -f tests\ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests\Docker\docker-compose.yml --profile standard up
+
+# DL205 quirks
+docker compose -f tests\ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests\Docker\docker-compose.yml --profile dl205 up
+
+# Mitsubishi MELSEC quirks
+docker compose -f tests\ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests\Docker\docker-compose.yml --profile mitsubishi up
+
+# Siemens S7-1500 MB_SERVER quirks
+docker compose -f tests\ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests\Docker\docker-compose.yml --profile s7_1500 up
+```
+
+Detached + stop:
+
+```powershell
+docker compose -f tests\...\Docker\docker-compose.yml --profile dl205 up -d
+docker compose -f tests\...\Docker\docker-compose.yml --profile dl205 down
+```
+
+Only one profile binds `:5020` at a time; switch by stopping the current
+service + starting another. The integration tests discriminate by a
+separate `MODBUS_SIM_PROFILE` env var so they skip correctly when the
+wrong profile is live.
+
+## Endpoint
+
+- Default: `localhost:5020`
+- Override with `MODBUS_SIM_ENDPOINT` (e.g. a real PLC on `:502`).
+
+## Run the integration tests
+
+In a separate shell with one profile live:
+
+```powershell
+cd C:\Users\dohertj2\Desktop\lmxopcua
+dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests
+```
+
+`ModbusSimulatorFixture` probes `localhost:5020` at collection init +
+records a `SkipReason` when unreachable, so tests stay green on a fresh
+clone without Docker running.
+
+## References
+
+- [`docs/drivers/Modbus-Test-Fixture.md`](../../../docs/drivers/Modbus-Test-Fixture.md) — coverage map + gap inventory
+- [`docs/v2/dev-environment.md`](../../../docs/v2/dev-environment.md) §Docker fixtures — full fixture inventory

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/docker-compose.yml

@@ -0,0 +1,79 @@
+# Modbus integration-test fixture — pymodbus simulator.
+#
+# One service per profile. Bring up only the profile a test class needs;
+# they all bind :5020 on the host so can't run concurrently. The compose
+# `profiles:` feature gates which service spins up via `--profile <name>`.
+#
+# Usage:
+#   docker compose --profile standard up
+#   docker compose --profile dl205 up
+#   docker compose --profile mitsubishi up
+#   docker compose --profile s7_1500 up
+services:
+  standard:
+    profiles: ["standard"]
+    build:
+      context: .
+      dockerfile: Dockerfile
+    image: otopcua-pymodbus:3.13.0
+    container_name: otopcua-pymodbus-standard
+    restart: "no"
+    ports:
+      - "5020:5020"
+    command: [
+      "pymodbus.simulator",
+      "--modbus_server", "srv",
+      "--modbus_device",  "dev",
+      "--json_file",      "/fixtures/standard.json"
+    ]
+
+  dl205:
+    profiles: ["dl205"]
+    image: otopcua-pymodbus:3.13.0
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: otopcua-pymodbus-dl205
+    restart: "no"
+    ports:
+      - "5020:5020"
+    command: [
+      "pymodbus.simulator",
+      "--modbus_server", "srv",
+      "--modbus_device",  "dev",
+      "--json_file",      "/fixtures/dl205.json"
+    ]
+
+  mitsubishi:
+    profiles: ["mitsubishi"]
+    image: otopcua-pymodbus:3.13.0
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: otopcua-pymodbus-mitsubishi
+    restart: "no"
+    ports:
+      - "5020:5020"
+    command: [
+      "pymodbus.simulator",
+      "--modbus_server", "srv",
+      "--modbus_device",  "dev",
+      "--json_file",      "/fixtures/mitsubishi.json"
+    ]
+
+  s7_1500:
+    profiles: ["s7_1500"]
+    image: otopcua-pymodbus:3.13.0
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: otopcua-pymodbus-s7_1500
+    restart: "no"
+    ports:
+      - "5020:5020"
+    command: [
+      "pymodbus.simulator",
+      "--modbus_server", "srv",
+      "--modbus_device",  "dev",
+      "--json_file",      "/fixtures/s7_1500.json"
+    ]

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/ModbusSimulatorFixture.cs

@@ -3,8 +3,8 @@ using System.Net.Sockets;
 namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests;
 
 /// <summary>
-///     Reachability probe for a Modbus TCP simulator (pymodbus-driven, see
-///     <c>Pymodbus/serve.ps1</c>) or a real PLC. Parses
+///     Reachability probe for a Modbus TCP simulator (pymodbus in Docker, see
+///     <c>Docker/docker-compose.yml</c>) or a real PLC. Parses
 ///     <c>MODBUS_SIM_ENDPOINT</c> (default <c>localhost:5020</c> per PR 43) and TCP-connects once at
 ///     fixture construction. Each test checks <see cref="SkipReason"/> and calls
 ///     <c>Assert.Skip</c> when the endpoint was unreachable, so a dev box without a running
@@ -28,7 +28,7 @@ public sealed class ModbusSimulatorFixture : IAsyncDisposable
 {
     // PR 43: default port is 5020 (pymodbus convention) instead of 502 (Modbus standard).
     // Picking 5020 sidesteps the privileged-port admin requirement on Windows + matches the
-    // port baked into the pymodbus simulator JSON profiles in Pymodbus/. Override with
+    // port baked into the pymodbus simulator JSON profiles in Docker/profiles/. Override with
     // MODBUS_SIM_ENDPOINT to point at a real PLC on its native port 502.
     private const string DefaultEndpoint = "localhost:5020";
     private const string EndpointEnvVar = "MODBUS_SIM_ENDPOINT";
@@ -61,15 +61,15 @@ public sealed class ModbusSimulatorFixture : IAsyncDisposable
             if (!task.Wait(TimeSpan.FromSeconds(2)) || !client.Connected)
             {
                 SkipReason = $"Modbus simulator at {Host}:{Port} did not accept a TCP connection within 2s. " +
-                             $"Start the pymodbus simulator (Pymodbus\\serve.ps1 -Profile standard) " +
+                             $"Start the pymodbus Docker container (docker compose -f Docker/docker-compose.yml --profile standard up -d) " +
                              $"or override {EndpointEnvVar}, then re-run.";
             }
         }
         catch (Exception ex)
         {
             SkipReason = $"Modbus simulator at {Host}:{Port} unreachable: {ex.GetType().Name}: {ex.Message}. " +
-                         $"Start the pymodbus simulator (Pymodbus\\serve.ps1 -Profile standard) " +
-                             $"or override {EndpointEnvVar}, then re-run.";
+                         $"Start the pymodbus Docker container (docker compose -f Docker/docker-compose.yml --profile standard up -d) " +
+                         $"or override {EndpointEnvVar}, then re-run.";
         }
     }