PR 3.3 — Wonderware sidecar pipe protocol + dispatcher

Sidecar now serves a length-prefixed, kind-tagged MessagePack pipe protocol
mirroring Galaxy.Host's: 4-byte BE length + 1-byte MessageKind + body, 16 MiB
cap. Hello handshake validates per-process shared secret + protocol major
version + caller SID via ImpersonateNamedPipeClient before any work frame
runs.

Five contract pairs ship in this PR:

  ReadRawRequest          ↔ ReadRawReply
  ReadProcessedRequest    ↔ ReadProcessedReply
  ReadAtTimeRequest       ↔ ReadAtTimeReply
  ReadEventsRequest       ↔ ReadEventsReply
  WriteAlarmEventsRequest ↔ WriteAlarmEventsReply

Timestamps cross the wire as DateTime ticks (long) to dodge MessagePack's
DateTime kind/timezone quirks; both sides convert with DateTime(ticks, Utc).
Sample values cross as MessagePack-serialized byte[] so the .NET 10 client
(PR 3.4) deserializes per the tag's mx_data_type without the sidecar needing
to know OPC UA types.

HistorianFrameHandler dispatches by MessageKind to IHistorianDataSource (the
PR 3.2 lifted interface) for reads, and to a new IAlarmEventWriter strategy
for the alarm-event persistence path. Per-call exceptions surface as
Success=false replies so a single bad request doesn't kill the connection.
WriteAlarmEvents replies carry per-event success flags; the SQLite
store-and-forward sink retries failed slots on the next drain tick.

Program.cs spins the pipe server when OTOPCUA_HISTORIAN_ENABLED=true. Pipe-
only mode (default false) preserves PR 3.1's smoke-test behaviour: the host
still validates env vars and waits for Ctrl-C, but doesn't initialize the
Wonderware SDK.

Sidecar test project gains 8 round-trip tests (37 total now): every contract
pair round-trips through FrameReader/FrameWriter via in-memory streams, the
handler surfaces historian exceptions cleanly, WriteAlarmEvents per-event
status flows through, and the no-writer-configured path returns a clean
error reply.

Added MessagePack 2.5.187 to the sidecar csproj.

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

docs/v2/modbus-addressing.md

@@ -169,6 +169,31 @@ Beyond per-tag addressing, `ModbusDriverOptions` exposes (#139–#143):
   bridge between adjacent register tags. With `MaxReadGap=10`, three tags
   at HR 100/102/110 collapse into one FC03 of quantity 11.
 
+### Coalescing auto-recovery (#148 / #150 / #151 / #152)
+- A coalesced read that fails with a Modbus exception (write-only or
+  protected register mid-block) records the failed range as
+  auto-prohibited. The planner stops re-coalescing across the range; the
+  per-tag fallback path keeps healthy members working in the same scan.
+- **Bisection (#150)**: every re-probe pass narrows multi-register
+  prohibitions by trying the two halves separately. Over log2(span)
+  ticks the prohibition pins at the actual offending register(s);
+  intermediate halves that succeed get cleared.
+- **Periodic re-probe (#151)**: opt in via
+  `AutoProhibitReprobeInterval` (TimeSpan?). Default null = disabled
+  (prohibitions persist for the driver lifetime; clear on
+  `ReinitializeAsync`).
+- **Per-tag escape hatch**: `CoalesceProhibited` (bool, default false)
+  on `ModbusTagDefinition`. The planner reads such tags in isolation
+  regardless of `MaxReadGap`. Use for known-bad addresses you want to
+  exclude from the auto-discovery loop.
+- **Diagnostics (#152)**: `ModbusDriver.GetAutoProhibitedRanges()`
+  returns a snapshot of every active prohibition as
+  `ModbusAutoProhibition` records (UnitId / Region / StartAddress /
+  EndAddress / LastProbedUtc / BisectionPending). Surface in the
+  driver-diagnostics RPC channel when that wiring lands; for now
+  consumable by in-process callers (Server health endpoints, log
+  aggregation).
+
 ## JSON DTO shape
 
 The factory accepts both the structured form (legacy) and the new

lmx_backend.md

@@ -0,0 +1,274 @@
+# Galaxy / LMX Backend — Restructuring Options
+
+## Context
+
+Today the Galaxy driver is structured very differently from every other driver
+in this repo:
+
+- **Galaxy.Proxy** (.NET 10, in-process): tiny shim that frames IPC to the host.
+- **Galaxy.Host** (.NET Framework 4.8 **x86**, NSSM-wrapped Windows service):
+  owns MXAccess COM, the STA pump, the ZB Galaxy Repository SQL queries, the
+  Wonderware Historian SDK plugin, the per-platform `ScanState` probe manager,
+  the alarm tracker (`.InAlarm`/`.Priority`/`.DescAttrName`/`.Acked` state
+  machine + ack writer), recycle policy, and post-mortem MMF.
+
+Other drivers (Modbus, S7, AB CIP, OpcUaClient, TwinCAT, FOCAS Tier-C) are
+**in-process Tier-A drivers** in the .NET 10 server. They do data + browse
+only; historian and alarming are driver-agnostic concerns at the server layer.
+
+A sibling project, **mxaccessgw**
+(`C:\Users\dohertj2\Desktop\mxaccessgw`), already provides:
+
+- A .NET 10 x64 gRPC gateway in front of per-session .NET 4.8 x86 worker
+  processes that own MXAccess COM, the STA, and event sinks
+  (`MxGateway.Server` + `MxGateway.Worker`).
+- A full MXAccess command + event surface (`Register`, `AddItem`, `Advise`,
+  `Write`, `WriteSecured`, `OnDataChange`, `OnWriteComplete`, etc.).
+- A cached, deploy-gated, paged **Galaxy Repository browse** RPC
+  (`galaxy_repository.v1`) reading the same ZB tables we read today, with the
+  query bodies kept byte-identical to OtOpcUa.
+- A .NET client library (`clients/dotnet/MxGateway.Client`).
+- API-key auth, Blazor dashboard, structured logs, metrics, watchdog/recycle.
+
+The proposal is to **strip Galaxy down to data + browse** — push historian and
+alarming out to server-level subsystems where they live for every other driver
+— and pick how the slimmed-down driver talks to MXAccess.
+
+---
+
+## What "push historian and alarming out" means
+
+Both options below assume the same scope reduction; they only differ in how
+the driver reaches MXAccess.
+
+| Concern | Today (Galaxy.Host) | After |
+|---|---|---|
+| Galaxy hierarchy browse | `GalaxyRepository` (SQL) inside Host | Driver (Option 1: via gw browse RPC; Option 2: own SQL or worker) |
+| Live read / write / subscribe | `MxAccessClient` + STA pump in Host | gw (Option 1) or embedded worker (Option 2) |
+| Wonderware Historian SDK | `HistorianDataSource` in Host (x86) | Separate Historian data source plugged into the server's HA service. Likely stays its own .NET 4.8 x86 sidecar because the SDK is x86-only; **independent of the Galaxy driver lifecycle**. |
+| Alarm state machine (`.InAlarm`/`.Acked` quartet, transitions, ack writer) | `GalaxyAlarmTracker` in Host | Server-level A&E subsystem subscribes to alarm-bearing attributes the driver advertises and runs the AlarmCondition state machine generically. Driver only flags `IsAlarm=true` in node metadata. |
+| `ScanState` per-platform probes | `GalaxyRuntimeProbeManager` in Host | Driver-side: ScanState is just another tag subscription; the driver re-advises one per discovered `$WinPlatform`/`$AppEngine` and reports `HostConnectivityStatus` from the value stream. No special host-side machinery. |
+
+After the strip-down, the Galaxy driver looks like Modbus or OpcUaClient: it
+discovers nodes, reads/writes/subscribes, and reports per-host transport
+health. Everything else is the server's problem.
+
+---
+
+## Option 1 — Tier-A driver against the MxAccess Gateway
+
+`Driver.Galaxy` becomes a regular **in-process .NET 10 driver** in the OtOpcUa
+server (no `.Host`, no `.Proxy` split, no x86). It talks to a separately
+deployed `MxGateway.Server` over gRPC using `MxGateway.Client`. Browse comes
+from `galaxy_repository.v1.DiscoverHierarchy`. Live data comes from
+`MxAccessGateway.OpenSession`/`AddItem`/`Advise`/`StreamEvents`.
+
+```
+OtOpcUa.Server (.NET 10 x64)
+  └── Driver.Galaxy (in-proc, .NET 10)
+        └── gRPC ──► MxGateway.Server (.NET 10 x64)
+                       └── pipe ──► MxGateway.Worker (.NET 4.8 x86)
+                                       └── MXAccess COM (STA)
+```
+
+### Pros
+
+- **Architectural parity with other drivers.** No bespoke `Host` service, no
+  x86 build target, no NSSM wrapper, no STA pump in this repo, no
+  `PostMortemMmf`/`RecyclePolicy` we maintain ourselves.
+- **OtOpcUa server stops needing AVEVA installed on its own host.** The
+  gateway runs where MXAccess lives; the OPC UA server can live on a different
+  box, in a container, or on a hardened jump host.
+- **One canonical MXAccess surface across the org.** Any future tool — a
+  diagnostic CLI, a Historian replacement, an integration harness — talks to
+  the same gw with the same parity guarantees we get.
+- **Multi-instance friendly.** Two OtOpcUa servers (warm/hot redundancy) share
+  one gw and one MXAccess footprint instead of each running their own
+  `Galaxy.Host` with duplicate Wonderware client identities.
+- **Browse + cache for free.** `galaxy_repository.v1` already implements the
+  hierarchy cache, deploy-time gating, paging, and `WatchDeployEvents` — we
+  delete `GalaxyRepository.cs`, `GalaxyHierarchyRow.cs`, the change-detection
+  poll loop, and the matching SQL plumbing.
+- **Operability for free.** API-key auth, Blazor dashboard at `/dashboard`,
+  metrics via `Meter`, structured logs with redaction. We currently have
+  none of that in `Galaxy.Host`.
+- **Future backend swap.** When AVEVA exposes managed NMX or another modern
+  path, gw routes to it without OtOpcUa changes (gw's stated roadmap).
+- **Tighter blast radius.** A hung COM event, a leaking COM object, a
+  crashing worker — all owned by gw's session/worker isolation, not the
+  OPC UA server process.
+- **Simpler version story for OtOpcUa.** Driver is plain .NET 10; the
+  bitness/runtime split lives entirely in mxaccessgw's repo.
+
+### Cons
+
+- **Extra deployment dependency.** mxaccessgw is now a service that has to be
+  installed, monitored, and kept on a compatible protocol version. For a
+  single-box install this is one more moving piece.
+- **Two hops on every call** (driver→gw, gw→worker) instead of one
+  (proxy→host). Today's hop is MessagePack over a named pipe; the new outer
+  hop is gRPC over TCP. Per-call overhead is a few hundred microseconds, not
+  a regression for OPC UA workloads but measurable for very chatty bursts.
+- **Auth/secret surface added.** OtOpcUa now holds an API key for gw and
+  rotates it; gw's SQLite-backed key store has to be managed.
+- **Failure model spans two processes we don't own** — gw + worker. Reconnect
+  logic in our driver has to ride both: gw transport drop, gw session lease
+  expiry, gw-detected worker crash, plus the worker's own MXAccess reconnect.
+  All of it is exposed in the gRPC contract, but it's still surface area.
+- **Cross-repo protocol coupling.** Bumping `mxaccessgw` major version (gRPC
+  contract changes, session shape changes) ripples into OtOpcUa releases.
+  Mitigated by versioned contracts; not free.
+- **Galaxy redundancy still has to think about gw.** A redundancy fail-over of
+  OtOpcUa is independent of the gw's session lifecycle. Need to decide whether
+  the standby holds an open session or only opens it on takeover.
+- **Sensitive writes (`WriteSecured`, `AuthenticateUser`) cross the network**
+  if gw is remote. TLS + mTLS solves it but adds setup.
+
+---
+
+## Option 2 — Embed mxaccessgw worker, no gateway
+
+`Driver.Galaxy` is still in-process .NET 10, but instead of speaking gRPC to a
+gateway service, it directly **launches and supervises one (or more)
+`MxGateway.Worker` processes** and talks to them over the same named-pipe
+worker protocol gw uses internally
+(`docs/WorkerFrameProtocol.md`, `docs/WorkerProcessLauncher.md`). Browse stays
+local — driver runs the SQL queries against ZB itself.
+
+```
+OtOpcUa.Server (.NET 10 x64)
+  └── Driver.Galaxy (in-proc, .NET 10)
+        ├── ZB SQL (local, in-proc)
+        └── pipe ──► MxGateway.Worker (.NET 4.8 x86, child process)
+                       └── MXAccess COM (STA)
+```
+
+### Pros
+
+- **One hop, not two.** Driver → worker pipe is the same shape as today's
+  Proxy → Host pipe. Latency is on par with the current implementation.
+- **No new service to deploy.** Worker is launched as a child process the
+  same way `Galaxy.Host` is launched today (just with mxaccessgw's worker
+  binary). Single-machine install story stays simple.
+- **Keeps the trust boundary local.** No API keys, no TLS, no exposed gRPC
+  port on the OtOpcUa box.
+- **Reuses mxaccessgw's parity-tested worker code** — STA pump, COM lifetime,
+  event conversion, fault model — without inheriting gw's ASP.NET Core /
+  Blazor / SQLite footprint.
+- **Tighter ownership.** OtOpcUa owns the worker lifecycle; recycle, kill,
+  restart, post-mortem all decided by the driver, not by an external service
+  we don't control.
+- **Easier to reason about during integration tests.** No second service to
+  spin up in CI; just a child process per test fixture.
+
+### Cons
+
+- **OtOpcUa server box must still have AVEVA + MXAccess installed**, since
+  the worker runs locally. The major deployment win of Option 1
+  (separating where MXAccess runs from where OtOpcUa runs) is lost.
+- **OtOpcUa still ships an x86 .NET 4.8 binary alongside it.** Even if we
+  vendor mxaccessgw's worker rather than write our own, installer complexity
+  and bitness considerations remain.
+- **We re-implement everything gw already gives.** Process supervision,
+  watchdog, recycle policy, heartbeat, post-mortem — these are exactly what
+  `Galaxy.Host` does today, and they'd live in our repo again, just calling a
+  different worker binary.
+- **No browse cache, no deploy gating, no `WatchDeployEvents`** — we keep
+  running our own ZB queries and our own `time_of_last_deploy` poll, or we
+  port gw's cache code into the driver. Either way it's duplicated logic.
+- **No auth, no dashboard, no metrics.** Operability stays where it is today
+  (i.e., minimal). Adding it ourselves is a separate project.
+- **Multiple OtOpcUa instances multiply MXAccess sessions.** Redundancy pair
+  → two MXAccess clients on the Galaxy from the same software, vs. Option 1
+  where one gw arbitrates.
+- **Worker protocol coupling without the contract surface.** We depend on
+  mxaccessgw's worker IPC frame format — a surface that mxaccessgw treats as
+  *internal* to its own gw↔worker boundary. If they refactor it, we have to
+  follow. The public gRPC contract (Option 1) is more stable by design.
+- **Loses the "common MXAccess access point" benefit.** Other consumers
+  (CLI, integration harnesses, future tools) can't share state with our
+  embedded worker.
+
+---
+
+## Status quo (for comparison)
+
+Keep `Galaxy.Host` as today, and in-place rip out historian + alarming +
+probe manager. End state: the Host shrinks to `MxAccessClient` + `GalaxyRepository`,
+which is roughly what Option 2 ends up looking like — but with our hand-rolled
+COM bridge instead of mxaccessgw's worker. Not a serious option once
+mxaccessgw exists; we'd be maintaining a parallel implementation of the same
+thing.
+
+---
+
+## Recommendation (effort-agnostic)
+
+**Go with Option 1 — Tier-A driver against the MxAccess Gateway.**
+
+The decisive arguments:
+
+1. **It's the only option that aligns Galaxy with how every other driver in
+   this repo is structured.** The user's stated goal — "keep lmx to data +
+   browsing, similar to other drivers" — only fully resolves if there is no
+   `.Host` and no x86 build artifact in this repo at all. Option 2 still has
+   an x86 child process and supervisor code; it's `Galaxy.Host` with a
+   different worker binary inside.
+
+2. **It separates *where MXAccess runs* from *where OtOpcUa runs*.** That is
+   a strategically larger win than a few hundred microseconds of per-call
+   latency. The OPC UA server stops being chained to AVEVA install footprint,
+   bitness, and Wonderware client identity — which removes a class of
+   deployment, redundancy, and CI problems we hit today (e.g., the
+   `DESKTOP-6JL3KKO` Hyper-V/Docker conflict, the `dohertj2`-only pipe ACL,
+   the live-Galaxy smoke test prerequisites).
+
+3. **It collapses scope.** A non-trivial fraction of `Galaxy.Host` (browse
+   cache, deploy-event watch, worker supervision, COM bridge, post-mortem,
+   recycle, ACL hardening) is reproduced *better* in mxaccessgw. Option 1
+   deletes our copy. Option 2 keeps it.
+
+4. **It positions historian and alarming for the right home.** Once the
+   Galaxy driver is "just another driver", historian becomes a server-level
+   data source (one that can also feed Modbus/S7 history if we ever want it),
+   and alarming becomes a server-level A&E subsystem. Option 2 nominally
+   allows the same move, but the temptation to keep them in `Galaxy.Host`
+   "while we're already there" is real.
+
+5. **It future-proofs against AVEVA's roadmap.** Managed NMX, ASB, or any
+   replacement that shows up over the next few years gets adopted in
+   mxaccessgw without a release in this repo.
+
+The case for Option 2 is real but narrow: it's the right call **only** if we
+commit to single-box deployments forever, refuse to take a gRPC dependency,
+and value local-trust simplicity over the consolidation/operability benefits
+gw provides. None of those constraints hold here.
+
+### What flips the recommendation
+
+- If the gw protocol is unstable or perf-tested under our subscription
+  patterns turns out worse than expected → revisit Option 2.
+- If org-policy forbids running an MXAccess gateway as its own service →
+  Option 2.
+- If Galaxy goes from one of several drivers to *the* primary driver and
+  raw call-rate matters more than architectural fit → revisit.
+
+Otherwise: Option 1.
+
+---
+
+## Out-of-scope follow-ups (don't decide here, but flag them)
+
+- **Where does the Wonderware Historian SDK live?** Likely its own
+  .NET 4.8 x86 sidecar exposing a small `IHistorianDataSource` over a pipe or
+  gRPC, plugged into the OPC UA server's HA service alongside any future
+  historian sources. Independent of which option above is chosen.
+- **Alarm subsystem ownership.** Decide whether the server hosts a generic
+  AlarmCondition state machine driven by driver-advertised alarm metadata, or
+  whether each driver continues to emit pre-shaped alarm transitions. Galaxy's
+  4-attr quartet is a strong forcing function for the generic approach.
+- **Redundancy + gw sessions.** Standby OtOpcUa holds an open gw session
+  (warm) vs. opens on takeover (cold). Affects gw worker count and Galaxy
+  client-identity collisions.
+- **Auth between OtOpcUa and gw.** API key in DPAPI-protected secret file vs.
+  Windows-auth gRPC. Both supported by gw; pick before rollout.

lmx_mxgw.md

@@ -0,0 +1,476 @@
+# Galaxy → MxAccessGateway Migration Plan
+
+Implements **Option 1** from `lmx_backend.md`: replace the bespoke `Galaxy.Host`
++ `Galaxy.Proxy` IPC pair with an **in-process Tier-A** `Driver.Galaxy` running
+in the .NET 10 OtOpcUa server, talking to a separately-deployed
+`MxGateway.Server` (mxaccessgw repo) over gRPC for live MXAccess work and
+Galaxy Repository browse.
+
+## Outcome
+
+After this work:
+
+- `OtOpcUa.Server` is fully .NET 10 x64 — no x86 build artifacts in this repo.
+- `Driver.Galaxy.Host` (Windows service, NSSM-wrapped, .NET 4.8 x86) is
+  retired. `Driver.Galaxy.Proxy` and `Driver.Galaxy.Shared` are deleted.
+  AVEVA platform is no longer required on the OtOpcUa box.
+- A new in-process `Driver.Galaxy` lives next to `Driver.Modbus`,
+  `Driver.OpcUaClient`, etc. It implements the same `IDriver` capability set
+  the proxy implements today, but its body calls `MxGateway.Client`
+  (`MxGatewayClient`, `MxGatewaySession`, `GalaxyRepositoryClient`).
+- Wonderware Historian SDK access moves out of the Galaxy driver into a
+  driver-agnostic historian data source (`Driver.Historian.Wonderware`,
+  separate sidecar, .NET 4.8 x86). The OPC UA HA service plugs into it the
+  same way it would plug into any future historian.
+- Alarm condition tracking moves out of the driver into the OPC UA server's
+  generic A&E subsystem. The driver only flags `IsAlarm=true` on attribute
+  metadata and forwards live `.InAlarm`/`.Acked`/etc value changes; the
+  server runs the AlarmCondition state machine.
+- Per-platform `ScanState` probes degrade to plain attribute subscriptions —
+  no special probe manager.
+
+---
+
+## Pre-flight: improvements to land in mxaccessgw first
+
+These are **integration-quality changes** in the mxaccessgw repo that make
+the OtOpcUa side dramatically simpler / faster / more robust. They aren't
+strictly required to start, but ship enough of them before phase 3 that we're
+not designing around gaps.
+
+### gw-1. Galaxy attribute metadata parity
+
+**What's there:** `galaxy_repository.v1.DiscoverHierarchy` returns
+`GalaxyObject` with name, parent, category, and dynamic attributes.
+
+**What's missing for OtOpcUa:** every field today's `MxAccessGalaxyBackend`
+copies into `GalaxyAttributeInfo` — confirm gw's `Attribute` proto carries:
+- `mx_data_type` (int)
+- `is_array` (bool)
+- `array_dimension` (uint, optional)
+- `security_classification` (int)
+- `is_historized` (bool, from `HistorizedExtension` primitive)
+- `is_alarm` (bool, from `AlarmExtension` primitive)
+
+If any are missing, add them to the proto and the server-side query mapper.
+Without `IsAlarm` and `IsHistorized` the OPC UA server can't decide which
+nodes get HasHistoricalConfiguration / which become AlarmConditions.
+
+### gw-2. Stable, documented event-stream resume semantics
+
+**What's needed:** the OtOpcUa driver must survive a transient gw transport
+drop without losing subscription state or duplicating change events. gw's
+`StreamEventsAsync(afterWorkerSequence)` already exposes resumption.
+Document the per-session retention window (how long does the worker buffer
+events the gateway hasn't acked?) and the "events were dropped, you must
+re-subscribe" signal. If retention is bounded by count rather than time,
+expose the bound in `OpenSessionReply` so the client can size its own buffer.
+
+### gw-3. Reconnectable sessions
+
+Listed under "post-v1 revisit" in `gateway.md`. Without it, every gw or
+OtOpcUa restart re-`Register`s, re-`AddItem`s, re-`Advise`s the entire
+address space — for a 50k-tag Galaxy that's a non-trivial cold-start. With
+reconnectable sessions, the driver presents its `SessionId` after a restart
+and the worker keeps its handles.
+
+If full reconnection is too large, ship a **bulk replay** instead: a single
+RPC that takes the full subscription set and the worker performs the
+register/add/advise inside one round trip. We can drive it from a
+client-side cache rather than gw state. See gw-5 below.
+
+### gw-4. Driver-shaped subscribe primitive
+
+`MxGatewaySession` already has `SubscribeBulkAsync` (one RPC: `Register`
+implicit + `AddItem` + `Advise` for a list of tag addresses, returning
+per-tag `SubscribeResult`). That's exactly what `ISubscribable.SubscribeAsync`
+wants. Confirm it returns enough per-tag detail to surface a partial-failure
+list to OPC UA monitored items (good handle, status code, error text).
+
+If not already, expose **`SubscribeBulk` with optional update-rate hint**
+forwarded to `SetBufferedUpdateInterval` so the OPC UA publishing interval
+becomes a single field on the subscribe call rather than a follow-up RPC.
+
+### gw-5. Subscription replay snapshot
+
+Provide an RPC `ReplaySubscriptionsAsync(SessionId, IEnumerable<TagAddress>)`
+that re-establishes a list of subscriptions after a session reset and returns
+per-tag results. The client stores its tag list locally (the driver already
+has it from `Discover`), and the gw worker turns it into one
+register/add/advise sequence. This is the minimum surface we need; full
+"reattach to a previous session by id" (gw-3) is a richer version of the
+same thing.
+
+### gw-6. Transport-health stream
+
+The gw already exposes worker / session health on its dashboard. Add a small
+streaming RPC `StreamSessionHealth(SessionId) → stream SessionHealth` so the
+OtOpcUa driver can surface "MXAccess transport up/down" to its
+`IHostConnectivityProbe` without faking it via probe-tag subscriptions.
+Today `MxAccessClient.ConnectionStateChanged` does this in-process; we want
+the same signal at the gw boundary.
+
+### gw-7. Optional .NET 10 client polish
+
+- Async-disposable session pattern is already there.
+- Add a **typed `MxValue` ⇄ `object` adapter** for the seven Galaxy types
+  OtOpcUa cares about (Boolean, Int32, Float, Double, String, DateTime,
+  arrays of the same). Today every consumer writes its own `MxValue.From<T>`
+  helpers; this shaves boilerplate from the driver.
+- Add a **`SubscribeWithCallback`** convenience wrapper that combines
+  `OpenSession` + `SubscribeBulk` + `StreamEvents` and routes events through
+  a delegate per tag. Keeps the OPC UA driver from re-implementing the
+  fan-out / sequencer pattern.
+
+### gw-8. Auth minimums
+
+Document API-key scoping as it applies to OtOpcUa: the server identity needs
+`session`, `invoke`, `event`, and `metadata:read` scopes. Provide a CLI to
+mint a key bound to those scopes for an OtOpcUa instance.
+
+### gw-9. Performance: bulk paths and value coalescing
+
+- Confirm `SubscribeBulkAsync` is implemented as a single MXAccess
+  `AddItem`+`Advise` loop on the worker, not N pipe round trips. If not, fix
+  before we drive 50k-tag Galaxies through it.
+- Expose `SetBufferedUpdateInterval` per session so OtOpcUa can request
+  buffered updates at the OPC UA publishing interval and get one batched
+  `OnBufferedDataChange` per tick rather than N `OnDataChange` events.
+
+These can all ship in mxaccessgw independently and improve every consumer.
+
+---
+
+## OtOpcUa-side improvements to land in parallel
+
+Some are forced by removing `Galaxy.Host`; others are quality-of-life.
+
+### ot-1. Promote `IHistorianDataSource` to a server-level extension point
+
+Today `IHistorianDataSource` is a Galaxy-internal abstraction in
+`Driver.Galaxy.Host`. Lift it to `OtOpcUa.Core.Abstractions` (or a similar
+home next to `IDriver`) and let the OPC UA HA service consume **any number
+of registered data sources** keyed by node namespace. Drivers don't own
+historian access; the server mounts data sources alongside drivers. This is
+the prerequisite that lets us move Wonderware Historian out of the Galaxy
+driver without losing the feature.
+
+### ot-2. Generic alarm condition state machine in the server
+
+Move the `.InAlarm`/`.Priority`/`.DescAttrName`/`.Acked` quartet handling
+out of `GalaxyAlarmTracker` into a server-level alarm subsystem keyed off the
+`IsAlarm=true` flag drivers set during discovery. The server subscribes to
+the four sub-attributes itself and runs the AlarmCondition state machine.
+Driver only:
+- declares `IsAlarm=true` in `DriverAttributeInfo`,
+- forwards plain attribute value changes (already done by `ISubscribable`).
+
+This is also a precondition for future drivers (Modbus DL205 alarm bits,
+S7 alarm DBs) to emit alarms without each writing their own tracker.
+
+### ot-3. Driver capabilities trim
+
+After ot-1 and ot-2, `Driver.Galaxy` no longer needs to implement:
+- `IHistoryProvider` (server's HA service handles it via Wonderware
+  historian data source)
+- `IAlarmHistorianWriter` (server's A&E historian, or kept generic — Galaxy
+  shouldn't own the SQLite path)
+- `IAlarmSource` ack route (server-level alarm subsystem writes back via the
+  driver's `IWritable.WriteAsync`, which the gw already supports)
+
+Keep:
+- `IDriver`, `ITagDiscovery`, `IReadable`, `IWritable`, `ISubscribable`,
+  `IRediscoverable`, `IHostConnectivityProbe`.
+
+### ot-4. Treat `time_of_last_deploy` as `IRediscoverable`'s pump
+
+Replace the Host-side change-detection poll with a managed
+`GalaxyRepositoryClient.WatchDeployEventsAsync` consumer in the driver.
+Each event raises `OnRediscoveryNeeded` with the new deploy time as the
+`scopeHint`. No polling code in this repo.
+
+### ot-5. Connection pool at the server, not the driver
+
+If the redundancy pair runs two OtOpcUa instances against one gw, both
+should share a single `GrpcChannel` per process (already gRPC default) but
+**different sessions** (one MXAccess client identity per OtOpcUa instance,
+not one shared session that fights over Wonderware client state). Encode
+the per-instance MXAccess client name in driver config — already partly
+there (`OTOPCUA_GALAXY_CLIENT_NAME`); make it explicit in the new driver's
+`appsettings.json` shape.
+
+---
+
+## Phased implementation
+
+Each phase is a working, mergeable slice. Keep `Galaxy.Host` running
+alongside the new driver until phase 7 — gated by a config switch
+`Galaxy:Backend = legacy-host | mxgateway`.
+
+### Phase 0 — pre-flight (mxaccessgw repo)
+
+Ship gw-1, gw-2, gw-4, gw-9 (the parity, performance, and contract bits the
+plan immediately depends on). gw-3, gw-5, gw-6, gw-7 can come during or
+after phase 5.
+
+**Exit:** local OtOpcUa dev box can `MxGatewayClient.Create` a client, open a
+session, `SubscribeBulkAsync` 100 tags, and observe `OnDataChange` events at
+the configured update rate.
+
+### Phase 1 — server-level historian extension point (ot-1)
+
+1. Extract `IHistorianDataSource` (and its DTOs `HistorianSample`,
+   `HistorianAggregateSample`, `HistoricalEvent`) from
+   `Driver.Galaxy.Host/Backend/Historian/` into
+   `src/ZB.MOM.WW.OtOpcUa.Core/Abstractions/Historian/`.
+2. Extend the OPC UA HA service to look up a registered
+   `IHistorianDataSource` per namespace and call into it for `HistoryRead`,
+   `HistoryReadProcessed`, `HistoryReadAtTime`, `HistoryReadEvents`. Drivers
+   stop implementing `IHistoryProvider` directly; the server proxies.
+3. Add a no-op default registration so drivers without history keep working.
+
+**Exit:** all current Galaxy history reads route through an
+`IHistorianDataSource` registered by `Driver.Galaxy.Host` (still legacy)
+without behavior change. Other drivers untouched.
+
+### Phase 2 — server-level alarm subsystem (ot-2)
+
+1. Add an `IAlarmConditionDeclaration` API on the address-space builder so
+   discovery can flag a node as alarm-bearing and supply the four
+   sub-attribute references.
+2. Add a hosted `AlarmConditionService` in the server that, on driver
+   `Discover`, subscribes to the four sub-attributes via the driver's own
+   `ISubscribable`, runs the state machine, and emits
+   `IAlarmSource.OnAlarmEvent` itself. Acks route back through the driver's
+   `IWritable.WriteAsync` to the `.AckMsg` attribute.
+3. Add Galaxy-specific defaults (sub-attribute naming) as a small adapter
+   so the same service can serve future drivers with different conventions.
+
+**Exit:** Galaxy alarms still work end-to-end; the tracker code that runs
+inside `Galaxy.Host` is dead but kept for the legacy-host backend path.
+
+### Phase 3 — Wonderware Historian sidecar (`Driver.Historian.Wonderware`)
+
+1. New solution project: `Driver.Historian.Wonderware`, .NET 4.8 x86,
+   console app + NSSM (mirrors today's Galaxy.Host packaging exactly,
+   minus Galaxy responsibilities).
+2. Hosts the existing `HistorianDataSource`, `HistorianClusterEndpointPicker`,
+   `HistorianHealthSnapshot` code lifted from `Galaxy.Host/Backend/Historian/`
+   and exposes them over a small named-pipe protocol (or local gRPC if
+   .NET 4.8 cost is acceptable; named pipe is simpler).
+3. Add `Driver.Historian.Wonderware.Client` — .NET 10 — implementing
+   `IHistorianDataSource` against the sidecar.
+4. Server registers it as a data source for the `Galaxy` namespace.
+
+**Exit:** OPC UA history reads work via the sidecar with the legacy-host
+backend still in place. We've decoupled history from MXAccess.
+
+### Phase 4 — new `Driver.Galaxy` against gw
+
+This is the meat. New project: `src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/`, .NET 10,
+in-process. Capabilities (post ot-3): `IDriver`, `ITagDiscovery`, `IReadable`,
+`IWritable`, `ISubscribable`, `IRediscoverable`, `IHostConnectivityProbe`.
+
+Shape:
+
+```
+Driver.Galaxy/
+  GalaxyDriver.cs            # IDriver root
+  Browse/
+    GalaxyDiscoverer.cs      # consumes GalaxyRepositoryClient.DiscoverHierarchyAsync
+    DataTypeMap.cs           # mx_data_type → DriverDataType
+    SecurityMap.cs           # security_classification → SecurityClassification
+  Runtime/
+    GalaxyMxSession.cs       # owns one MxGatewaySession; Register + map per-driver client name
+    SubscriptionRegistry.cs  # tag → server/item handles; persists to memory only
+    EventPump.cs             # consumes session.StreamEventsAsync, fans out to OnDataChange
+    ReconnectSupervisor.cs   # gw transport drop / session-lost recovery
+    DeployWatcher.cs         # GalaxyRepositoryClient.WatchDeployEventsAsync → OnRediscoveryNeeded
+  Health/
+    HostConnectivityForwarder.cs  # gw-6 SessionHealth → IHostConnectivityProbe
+  Config/
+    GalaxyDriverOptions.cs   # endpoint, ApiKey, ClientName, TLS, retry, intervals
+  GalaxyDriverFactoryExtensions.cs  # AddGalaxyDriver(IServiceCollection)
+```
+
+Key behaviors:
+
+- **Discovery** calls `GalaxyRepositoryClient.DiscoverHierarchyAsync()`
+  once at init and on every `WatchDeployEvents` event, then drives the
+  address space builder. Same node naming as today (parent contained-name
+  hierarchy + leaf attributes named `tag_name.AttributeName`).
+- **Read** uses one-off `AddItem` + `Advise` + read-after-first-callback
+  is overkill; instead, use **`Register` + per-call `AddItem`/`Read`** if gw
+  exposes a synchronous read, otherwise short-lived advise. *Action item:*
+  confirm gw's read story; if absent, request a synchronous `ReadAsync` RPC
+  on top of MXAccess `Read` (which exists in the COM API).
+- **Write** maps `WriteRequest.Value` to `MxValue` via gw-7 helpers and
+  calls `WriteAsync(serverHandle, itemHandle, value, userId=0)`. Routes
+  `WriteSecured` (where `SecurityClassification == SecuredWrite/Verified`)
+  to `WriteSecuredAsync` once exposed on `MxGatewaySession`.
+- **Subscribe** calls `SubscribeBulkAsync` once per `ISubscribable.Subscribe`
+  call. Stores `(tag → itemHandle, sid)` in `SubscriptionRegistry`. The
+  single `EventPump` consumes one `StreamEventsAsync` per session and fans
+  out per `sid`.
+- **Unsubscribe** calls `UnsubscribeBulkAsync` and drops registry entries.
+- **Reconnect** — when the gRPC channel drops or `StreamEvents` returns,
+  `ReconnectSupervisor` reopens the session and replays subscriptions via
+  gw-5 `ReplaySubscriptionsAsync`. The driver flags `DriverState.Degraded`
+  during recovery; the server keeps publishing last-good values with
+  `Uncertain` quality.
+- **Host connectivity** — single synthesized host entry named after
+  `OTOPCUA_GALAXY_CLIENT_NAME` driven by gw-6 `SessionHealth` updates
+  (or, until gw-6 lands, by transport drops).
+
+Wire into the server next to other Tier-A drivers in the
+`AddDrivers(...)` call site.
+
+**Exit:** flipping `Galaxy:Backend` to `mxgateway` runs the OPC UA server
+end-to-end with no `Galaxy.Host` involvement. Live read, live write, live
+subscribe pass against the dev Galaxy. Historian + alarms still work via
+phases 1–3.
+
+### Phase 5 — parity test matrix
+
+Reuse the existing live-Galaxy integration tests; run each scenario twice:
+once with `Galaxy:Backend=legacy-host`, once with `mxgateway`. Compare:
+
+- discovered hierarchy node count + names + datatypes,
+- subscribed publish rates (allow ±10% tolerance vs. legacy),
+- write success / status codes for each `SecurityClassification`,
+- alarm condition transitions (Active / Acked / Inactive) — already
+  routed through phase 2's server-level subsystem,
+- history reads — phase 3 sidecar, identical results both backends,
+- reconnect behavior under gw kill, worker kill, network drop, ZB drop.
+
+Document the matrix; resolve every discrepancy or explicitly accept it.
+
+**Exit:** parity matrix has zero unexplained deltas. Performance budget
+agreed: e.g. ≤ 2× per-call latency vs. named-pipe baseline at the 95th
+percentile, equal or better throughput in `SubscribeBulk` setup time.
+
+### Phase 6 — perf + hardening
+
+- Land gw-9 buffered-update intervals.
+- Add OpenTelemetry traces from the driver around every gw call,
+  correlated via `client_correlation_id`.
+- Write soak test: 50k tags subscribed, 24h, count missed events, gw
+  restarts, OtOpcUa restarts.
+- Tune `MxGatewayClientOptions.MaxGrpcMessageBytes`, retry pipeline,
+  call timeouts based on soak results.
+
+**Exit:** production-acceptable perf numbers documented in
+`docs/Galaxy.Driver.md`.
+
+### Phase 7 — retirement
+
+1. Default `Galaxy:Backend = mxgateway` everywhere (sample configs,
+   install scripts, e2e configs).
+2. Delete `src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host`,
+   `src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy`,
+   `src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared`, and matching tests.
+3. Remove `OtOpcUaGalaxyHost` NSSM registration from
+   `scripts/install/Install-Services.ps1`. Add a registration block for the
+   Wonderware historian sidecar from phase 3.
+4. Remove every x86 .NET 4.8 reference, build target, and CI step from this
+   repo; remove `mxaccess_documentation.md`-driven dependencies that no
+   longer apply.
+5. Update CLAUDE.md, `docs/v2/dev-environment.md`, `docs/ServiceHosting.md`,
+   `docs/Redundancy.md` to reflect the new topology.
+6. Memory housekeeping: retire `project_galaxy_host_service.md` and
+   `project_galaxy_host_installed.md`; add a short note about the gw
+   dependency.
+
+**Exit:** `git grep -i 'Galaxy\.Host'` returns nothing in source.
+
+---
+
+## Configuration shape (new driver)
+
+```jsonc
+"Drivers": {
+  "Galaxy": {
+    "Type": "Galaxy",
+    "InstanceId": "galaxy-prod-1",
+    "Gateway": {
+      "Endpoint": "https://mxgw.aveva.local:5001",
+      "ApiKeySecretRef": "galaxy:apiKey",        // resolved via existing secret store
+      "UseTls": true,
+      "CaCertificatePath": "C:\\publish\\mxgw\\ca.crt",
+      "ConnectTimeoutSeconds": 10,
+      "DefaultCallTimeoutSeconds": 5,
+      "StreamTimeoutSeconds": 0                   // unbounded
+    },
+    "MxAccess": {
+      "ClientName": "OtOpcUa-A",                  // unique per OtOpcUa instance
+      "PublishingIntervalMs": 1000,               // hint for SetBufferedUpdateInterval
+      "WriteUserId": 0
+    },
+    "Repository": {
+      "DiscoverPageSize": 5000,
+      "WatchDeployEvents": true
+    },
+    "Reconnect": {
+      "InitialBackoffMs": 500,
+      "MaxBackoffMs": 30000,
+      "ReplayOnSessionLost": true
+    }
+  }
+}
+```
+
+The OtOpcUa secret store already handles DPAPI-protected values for LDAP
+binds; reuse it for the gw API key. Never put the key in plaintext in the
+sample config.
+
+---
+
+## Risks and mitigations
+
+| Risk | Mitigation |
+|---|---|
+| gw protocol regression breaks production | Pin gw NuGet to a contract version range; CI runs parity matrix on every gw bump; staged rollout via `Galaxy:Backend` flag. |
+| Per-call latency regresses for chatty workloads | Land gw-9 (buffered updates) before phase 5; soak the 95p in phase 6. |
+| Reconnect storm after gw restart re-registers 50k tags | Land gw-3 or gw-5 before phase 6; client-side bulk replay throttled by `SubscribeBulkAsync` chunk size. |
+| Alarm parity gap from moving tracker server-side | Phase 2 ships before phase 4; parity matrix gates phase 7. |
+| Historian sidecar adds a second .NET 4.8 x86 service | Acceptable: it's a *driver-agnostic* component, and it ships only where Wonderware historian access is actually needed. |
+| Two OtOpcUa instances both registering as same MXAccess client | `ClientName` is per-instance config (ot-5); install scripts lint that the redundancy pair has distinct names. |
+| Cross-machine MXAccess writes traverse plaintext gRPC | Phase 0 enforces `UseTls=true` for any non-loopback `Endpoint`; CI lints the sample configs. |
+| gw API key leaked in logs | gw and `MxGatewayClient` already redact `authorization` metadata; phase 6 audit. |
+| Memory leak in `EventPump` under high event rate | Bounded channel between `StreamEventsAsync` and per-sub fan-out, drop-newest with a metric counter; soak test catches. |
+
+---
+
+## Cross-cutting deliverables
+
+- **Docs:** `docs/v2/Galaxy.Driver.md` (new), updates to
+  `docs/v2/dev-environment.md`, `docs/ServiceHosting.md`,
+  `docs/Redundancy.md`, `CLAUDE.md`.
+- **Install scripts:** `scripts/install/Install-Services.ps1` removes
+  `OtOpcUaGalaxyHost`, adds `OtOpcUaWonderwareHistorian`, no Galaxy
+  service registration on the OtOpcUa node.
+- **e2e:** `scripts/e2e/e2e-config.sample.json` — drop `OTOPCUA_GALAXY_*`
+  pipe vars, add `Drivers:Galaxy:Gateway:Endpoint` etc.
+- **Memory:** retire stale Galaxy.Host entries; add gw dependency entry,
+  redundancy + client-name guidance.
+
+---
+
+## Order-of-work summary
+
+```
+Phase 0 (gw repo):  gw-1, gw-2, gw-4, gw-9
+Phase 1 (this):     ot-1   — historian extension point
+Phase 2 (this):     ot-2   — alarm subsystem
+Phase 3 (this):     Driver.Historian.Wonderware sidecar
+Phase 4 (this):     Driver.Galaxy (new) behind backend flag
+                     — depends on Phase 0, 1, 2
+Phase 5 (this+gw):  parity matrix
+                     — drives gw-3 / gw-5 / gw-6 / gw-7 if gaps surface
+Phase 6 (this):     perf + hardening
+Phase 7 (this):     retire Galaxy.Host / Proxy / Shared
+```
+
+Phases 1–3 are independent of each other and can run in parallel. Phase 4
+needs all three plus Phase 0. Phase 5 requires Phase 4. Phases 6 and 7 are
+sequential after Phase 5.

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Clusters/ClusterDetail.razor

@@ -51,6 +51,7 @@ else
         <li class="nav-item"><button class="nav-link @Tab("uns")" @onclick='() => _tab = "uns"'>UNS Structure</button></li>
         <li class="nav-item"><button class="nav-link @Tab("namespaces")" @onclick='() => _tab = "namespaces"'>Namespaces</button></li>
         <li class="nav-item"><button class="nav-link @Tab("drivers")" @onclick='() => _tab = "drivers"'>Drivers</button></li>
+        <li class="nav-item"><button class="nav-link @Tab("tags")" @onclick='() => _tab = "tags"'>Tags</button></li>
         <li class="nav-item"><button class="nav-link @Tab("acls")" @onclick='() => _tab = "acls"'>ACLs</button></li>
         <li class="nav-item"><button class="nav-link @Tab("redundancy")" @onclick='() => _tab = "redundancy"'>Redundancy</button></li>
         <li class="nav-item"><button class="nav-link @Tab("audit")" @onclick='() => _tab = "audit"'>Audit</button></li>
@@ -89,6 +90,10 @@ else
     {
         <DriversTab GenerationId="@_currentDraft.GenerationId" ClusterId="@ClusterId"/>
     }
+    else if (_tab == "tags" && _currentDraft is not null)
+    {
+        <TagsTab GenerationId="@_currentDraft.GenerationId" ClusterId="@ClusterId"/>
+    }
     else if (_tab == "acls" && _currentDraft is not null)
     {
         <AclsTab GenerationId="@_currentDraft.GenerationId" ClusterId="@ClusterId"/>

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Clusters/TagsTab.razor

@@ -0,0 +1,372 @@
+@using System.Text.Json
+@using ZB.MOM.WW.OtOpcUa.Admin.Components.Pages.Modbus
+@using ZB.MOM.WW.OtOpcUa.Admin.Services
+@using ZB.MOM.WW.OtOpcUa.Configuration.Entities
+@using ZB.MOM.WW.OtOpcUa.Configuration.Enums
+@using ZB.MOM.WW.OtOpcUa.Driver.Modbus
+@inject TagService TagSvc
+@inject DriverInstanceService DriverSvc
+@inject EquipmentService EquipmentSvc
+
+@*
+    #155 — interactive Tag CRUD scoped to a draft generation. Conditional editor: when the
+    selected DriverInstance is Modbus, the address input switches to ModbusAddressEditor (#145)
+    so users get the live-parse preview + grammar validation. Other driver types fall back to
+    a generic JSON textarea, matching the DriversTab pattern from #147.
+*@
+
+<div class="d-flex justify-content-between mb-3">
+    <h4>Tags (draft gen @GenerationId)</h4>
+    <button class="btn btn-primary btn-sm" @onclick="StartAdd">Add tag</button>
+</div>
+
+<div class="row g-3 mb-3">
+    <div class="col-md-4">
+        <label class="form-label small text-muted">Filter by driver</label>
+        <select class="form-select form-select-sm" @bind="_filterDriverId" @bind:after="ReloadAsync">
+            <option value="">— all drivers —</option>
+            @if (_drivers is not null)
+            {
+                @foreach (var d in _drivers)
+                {
+                    <option value="@d.DriverInstanceId">@d.Name (@d.DriverType)</option>
+                }
+            }
+        </select>
+    </div>
+</div>
+
+@if (_tags is null) { <p>Loading…</p> }
+else if (_tags.Count == 0 && !_showForm) { <p class="text-muted">No tags in this filter.</p> }
+else if (_tags.Count > 0)
+{
+    <table class="table table-sm">
+        <thead>
+            <tr><th>Name</th><th>Driver</th><th>Equipment</th><th>DataType</th><th>Access</th><th>TagConfig</th><th></th></tr>
+        </thead>
+        <tbody>
+        @foreach (var t in _tags)
+        {
+            <tr>
+                <td>@t.Name</td>
+                <td><code>@t.DriverInstanceId</code></td>
+                <td>@(t.EquipmentId ?? "—")</td>
+                <td>@t.DataType</td>
+                <td>@t.AccessLevel</td>
+                <td class="font-monospace small text-truncate" style="max-width:18rem">@t.TagConfig</td>
+                <td>
+                    <button class="btn btn-sm btn-outline-secondary me-1" @onclick="() => StartEdit(t)">Edit</button>
+                    <button class="btn btn-sm btn-outline-danger" @onclick="() => DeleteAsync(t.TagRowId)">Remove</button>
+                </td>
+            </tr>
+        }
+        </tbody>
+    </table>
+}
+
+@if (_showForm)
+{
+    <div class="card mt-3">
+        <div class="card-body">
+            <h5>@(_editMode ? "Edit tag" : "New tag")</h5>
+            <div class="row g-3">
+                <div class="col-md-4">
+                    <label class="form-label">Name</label>
+                    <input class="form-control" @bind="_draft.Name"/>
+                </div>
+                <div class="col-md-4">
+                    <label class="form-label">DriverInstance</label>
+                    <select class="form-select" @bind="_draft.DriverInstanceId" @bind:after="OnDriverChanged">
+                        <option value="">— select driver —</option>
+                        @if (_drivers is not null)
+                        {
+                            @foreach (var d in _drivers) { <option value="@d.DriverInstanceId">@d.Name (@d.DriverType)</option> }
+                        }
+                    </select>
+                </div>
+                <div class="col-md-4">
+                    <label class="form-label">Equipment (optional)</label>
+                    <select class="form-select" @bind="_draft.EquipmentId">
+                        <option value="">— none (folder-path mode) —</option>
+                        @if (_equipment is not null)
+                        {
+                            @foreach (var e in _equipment) { <option value="@e.EquipmentId">@e.Name</option> }
+                        }
+                    </select>
+                </div>
+                <div class="col-md-4">
+                    <label class="form-label">DataType</label>
+                    <input class="form-control" @bind="_draft.DataType" placeholder="Boolean / Int32 / Float / etc."/>
+                </div>
+                <div class="col-md-4">
+                    <label class="form-label">AccessLevel</label>
+                    <select class="form-select" @bind="_draft.AccessLevel">
+                        @foreach (var a in Enum.GetValues<TagAccessLevel>())
+                        {
+                            <option value="@a">@a</option>
+                        }
+                    </select>
+                </div>
+                <div class="col-md-4">
+                    <div class="form-check mt-4">
+                        <input type="checkbox" class="form-check-input" @bind="_draft.WriteIdempotent"/>
+                        <label class="form-check-label">WriteIdempotent</label>
+                    </div>
+                </div>
+            </div>
+
+            <div class="mt-3">
+                @if (_isModbus)
+                {
+                    <ModbusAddressEditor @bind-AddressString="_modbusAddress"
+                                         @bind-AddressString:after="OnAddressChanged"/>
+                }
+                else
+                {
+                    <label class="form-label">TagConfig (driver-specific JSON or string)</label>
+                    <textarea class="form-control font-monospace" rows="3" @bind="_draft.TagConfig"
+                              placeholder='@("{\"address\": ...}")'></textarea>
+                }
+            </div>
+
+            @* #156 — advanced Modbus fields. Collapsed by default; the basic form covers the
+               typical edit workflow. Expander surfaces Deadband (#141) / UnitId override (#142) /
+               CoalesceProhibited (#143) for the multi-slave / noisy-analog / protected-hole
+               deployments. Save-side flushes these into TagConfig as a structured JSON object
+               that ModbusTagDto's BuildTag honours alongside the address string. *@
+            @if (_isModbus)
+            {
+                <div class="mt-3">
+                    <button type="button" class="btn btn-sm btn-link p-0"
+                            @onclick="() => _showAdvanced = !_showAdvanced">
+                        @(_showAdvanced ? "▼ Advanced" : "▶ Advanced") (Deadband / UnitId override / CoalesceProhibited)
+                    </button>
+                </div>
+                @if (_showAdvanced)
+                {
+                    <div class="row g-3 mt-1 ps-3 border-start">
+                        <div class="col-md-4">
+                            <label class="form-label small">Deadband
+                                <span class="text-muted">(numeric scalar types only)</span>
+                            </label>
+                            <input type="number" step="any" class="form-control form-control-sm"
+                                   @bind="_advancedDeadband" @bind:after="OnAdvancedChanged"
+                                   placeholder="e.g. 0.5"/>
+                            <div class="form-text">Suppress publishes when |new - last| &lt; threshold.</div>
+                        </div>
+                        <div class="col-md-4">
+                            <label class="form-label small">UnitId override
+                                <span class="text-muted">(0–255, blank = use driver default)</span>
+                            </label>
+                            <input type="number" min="0" max="255" class="form-control form-control-sm"
+                                   @bind="_advancedUnitId" @bind:after="OnAdvancedChanged"
+                                   placeholder="leave blank for driver-level"/>
+                            <div class="form-text">Per-tag MBAP unit ID. Required when fronting a multi-slave gateway.</div>
+                        </div>
+                        <div class="col-md-4">
+                            <label class="form-label small">CoalesceProhibited</label>
+                            <div class="form-check mt-1">
+                                <input type="checkbox" class="form-check-input"
+                                       @bind="_advancedCoalesceProhibited" @bind:after="OnAdvancedChanged"/>
+                                <label class="form-check-label">Read in isolation (#143)</label>
+                            </div>
+                            <div class="form-text">Use when surrounding registers are write-only or fault on read.</div>
+                        </div>
+                    </div>
+                }
+            }
+
+            @if (_error is not null) { <div class="alert alert-danger mt-3">@_error</div> }
+
+            <div class="mt-3">
+                <button class="btn btn-sm btn-primary" @onclick="SaveAsync">Save</button>
+                <button class="btn btn-sm btn-secondary ms-2" @onclick="Cancel">Cancel</button>
+            </div>
+        </div>
+    </div>
+}
+
+@code {
+    [Parameter] public long GenerationId { get; set; }
+    [Parameter] public string ClusterId { get; set; } = string.Empty;
+
+    private List<Tag>? _tags;
+    private List<DriverInstance>? _drivers;
+    private List<Equipment>? _equipment;
+    private string _filterDriverId = string.Empty;
+
+    private bool _showForm;
+    private bool _editMode;
+    private Tag _draft = NewBlankDraft();
+    private string? _error;
+    private bool _isModbus;
+    private string? _modbusAddress;
+
+    // #156 — advanced Modbus fields. Bound separately from _draft.TagConfig because they
+    // round-trip through a structured JSON shape, not a single string. Synced into TagConfig
+    // by OnAdvancedChanged / OnAddressChanged (whichever fires).
+    private bool _showAdvanced;
+    private double? _advancedDeadband;
+    private byte? _advancedUnitId;
+    private bool _advancedCoalesceProhibited;
+
+    private static Tag NewBlankDraft() => new()
+    {
+        TagId = string.Empty, DriverInstanceId = string.Empty, Name = string.Empty,
+        DataType = "Int32", AccessLevel = TagAccessLevel.Read, TagConfig = string.Empty,
+    };
+
+    protected override async Task OnParametersSetAsync()
+    {
+        _drivers = await DriverSvc.ListAsync(GenerationId, CancellationToken.None);
+        _equipment = await EquipmentSvc.ListAsync(GenerationId, CancellationToken.None);
+        await ReloadAsync();
+    }
+
+    private async Task ReloadAsync()
+    {
+        _tags = await TagSvc.ListAsync(GenerationId,
+            string.IsNullOrWhiteSpace(_filterDriverId) ? null : _filterDriverId,
+            equipmentId: null,
+            CancellationToken.None);
+    }
+
+    private void StartAdd()
+    {
+        _draft = NewBlankDraft();
+        _editMode = false;
+        _modbusAddress = null;
+        _isModbus = false;
+        _error = null;
+        _showForm = true;
+        ResetAdvanced();
+    }
+
+    private void ResetAdvanced()
+    {
+        _showAdvanced = false;
+        _advancedDeadband = null;
+        _advancedUnitId = null;
+        _advancedCoalesceProhibited = false;
+    }
+
+    private void StartEdit(Tag row)
+    {
+        _draft = new Tag
+        {
+            TagRowId = row.TagRowId,
+            GenerationId = row.GenerationId,
+            TagId = row.TagId,
+            DriverInstanceId = row.DriverInstanceId,
+            DeviceId = row.DeviceId,
+            EquipmentId = row.EquipmentId,
+            Name = row.Name,
+            FolderPath = row.FolderPath,
+            DataType = row.DataType,
+            AccessLevel = row.AccessLevel,
+            WriteIdempotent = row.WriteIdempotent,
+            PollGroupId = row.PollGroupId,
+            TagConfig = row.TagConfig,
+        };
+        _editMode = true;
+        OnDriverChanged();
+        // Try to extract addressString + advanced fields from existing JSON config so the
+        // form pre-fills correctly when an operator hits Edit on an existing row.
+        ResetAdvanced();
+        if (_isModbus) HydrateModbusFromTagConfig(row.TagConfig);
+        _error = null;
+        _showForm = true;
+    }
+
+    private void HydrateModbusFromTagConfig(string tagConfig)
+    {
+        try
+        {
+            using var doc = JsonDocument.Parse(tagConfig);
+            var root = doc.RootElement;
+            if (root.TryGetProperty("addressString", out var addr) && addr.ValueKind == JsonValueKind.String)
+                _modbusAddress = addr.GetString();
+            if (root.TryGetProperty("deadband", out var db) && db.ValueKind is JsonValueKind.Number)
+                _advancedDeadband = db.GetDouble();
+            if (root.TryGetProperty("unitId", out var uid) && uid.ValueKind is JsonValueKind.Number)
+                _advancedUnitId = uid.GetByte();
+            if (root.TryGetProperty("coalesceProhibited", out var cp) && cp.ValueKind is JsonValueKind.True or JsonValueKind.False)
+                _advancedCoalesceProhibited = cp.GetBoolean();
+
+            // Auto-expand the advanced panel when any of those fields was actually set so
+            // operators see immediately what's been configured.
+            if (_advancedDeadband.HasValue || _advancedUnitId.HasValue || _advancedCoalesceProhibited)
+                _showAdvanced = true;
+        }
+        catch { /* Malformed JSON falls back to empty advanced state. */ }
+    }
+
+    private void OnDriverChanged()
+    {
+        var driver = _drivers?.FirstOrDefault(d => d.DriverInstanceId == _draft.DriverInstanceId);
+        _isModbus = driver is not null
+            && string.Equals(driver.DriverType, "Modbus", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private void OnAddressChanged() => RefreshTagConfigJson();
+    private void OnAdvancedChanged() => RefreshTagConfigJson();
+
+    /// <summary>
+    ///     Re-serializes the current address + advanced fields into TagConfig as a structured
+    ///     JSON object. ModbusTagDto's BuildTag honours every field — addressString drives
+    ///     the parser, while the structured bits (deadband / unitId / coalesceProhibited)
+    ///     pass through directly. Fields with default / empty values are omitted from the
+    ///     JSON to keep diffs in the existing draft-diff viewer clean.
+    /// </summary>
+    private void RefreshTagConfigJson()
+    {
+        if (string.IsNullOrWhiteSpace(_modbusAddress)
+            && !_advancedDeadband.HasValue
+            && !_advancedUnitId.HasValue
+            && !_advancedCoalesceProhibited)
+        {
+            return;
+        }
+
+        var payload = new Dictionary<string, object?>();
+        if (!string.IsNullOrWhiteSpace(_modbusAddress)) payload["addressString"] = _modbusAddress;
+        if (_advancedDeadband.HasValue)                  payload["deadband"] = _advancedDeadband.Value;
+        if (_advancedUnitId.HasValue)                    payload["unitId"] = _advancedUnitId.Value;
+        if (_advancedCoalesceProhibited)                 payload["coalesceProhibited"] = true;
+
+        _draft.TagConfig = JsonSerializer.Serialize(payload);
+    }
+
+    private void Cancel()
+    {
+        _showForm = false;
+        _editMode = false;
+    }
+
+    private async Task SaveAsync()
+    {
+        _error = null;
+        try
+        {
+            if (string.IsNullOrWhiteSpace(_draft.Name) || string.IsNullOrWhiteSpace(_draft.DriverInstanceId))
+            {
+                _error = "Name and DriverInstance are required.";
+                return;
+            }
+            if (_editMode)
+                await TagSvc.UpdateAsync(_draft, CancellationToken.None);
+            else
+                await TagSvc.CreateAsync(GenerationId, _draft, CancellationToken.None);
+            _showForm = false;
+            _editMode = false;
+            await ReloadAsync();
+        }
+        catch (Exception ex) { _error = ex.Message; }
+    }
+
+    private async Task DeleteAsync(Guid id)
+    {
+        await TagSvc.DeleteAsync(id, CancellationToken.None);
+        await ReloadAsync();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Modbus/ModbusDiagnostics.razor

@@ -0,0 +1,120 @@
+@page "/modbus/diagnostics/{DriverInstanceId}"
+@using ZB.MOM.WW.OtOpcUa.Admin.Services
+@inject DriverDiagnosticsClient Diagnostics
+
+@*
+    #154 — operator-facing view of the Server's auto-prohibition state for a Modbus driver.
+    Fetches via DriverDiagnosticsClient (HttpClient against the Server's HealthEndpointsHost).
+    Refreshes on demand; auto-refresh is a future task once a SignalR diag channel exists.
+*@
+
+<PageTitle>Modbus diagnostics — @DriverInstanceId</PageTitle>
+
+<div class="container py-4">
+    <h1>Modbus auto-prohibitions</h1>
+    <p class="text-muted">
+        Driver instance <code>@DriverInstanceId</code>. Live snapshot of coalesced ranges
+        the planner has learned to read individually (#148 / #150 / #151 / #152).
+    </p>
+
+    <div class="mb-3">
+        <button class="btn btn-sm btn-outline-primary" @onclick="LoadAsync" disabled="@_loading">
+            @(_loading ? "Loading…" : "Refresh")
+        </button>
+        @if (_lastRefreshed is not null)
+        {
+            <span class="text-muted ms-3 small">Last refreshed @_lastRefreshed.Value.ToLocalTime().ToString("HH:mm:ss")</span>
+        }
+    </div>
+
+    @if (_error is not null)
+    {
+        <div class="alert alert-danger">@_error</div>
+    }
+    else if (_response is null)
+    {
+        <p class="text-muted">Click <strong>Refresh</strong> to load.</p>
+    }
+    else if (_response.Count == 0)
+    {
+        <div class="alert alert-success">No auto-prohibitions. The planner is coalescing freely.</div>
+    }
+    else
+    {
+        <table class="table table-sm">
+            <thead>
+                <tr>
+                    <th>Unit</th>
+                    <th>Region</th>
+                    <th>Start</th>
+                    <th>End</th>
+                    <th>Span</th>
+                    <th>Status</th>
+                    <th>Last probed</th>
+                </tr>
+            </thead>
+            <tbody>
+            @foreach (var r in _response.Ranges.OrderBy(r => r.UnitId).ThenBy(r => r.Region).ThenBy(r => r.StartAddress))
+            {
+                <tr>
+                    <td><code>@r.UnitId</code></td>
+                    <td><code>@r.Region</code></td>
+                    <td><code>@r.StartAddress</code></td>
+                    <td><code>@r.EndAddress</code></td>
+                    <td>@(r.EndAddress - r.StartAddress + 1)</td>
+                    <td>
+                        @if (r.BisectionPending)
+                        {
+                            <span class="badge bg-warning text-dark">BISECTING</span>
+                        }
+                        else
+                        {
+                            <span class="badge bg-danger">ISOLATED</span>
+                        }
+                    </td>
+                    <td class="small text-muted">@FormatTimeSince(r.LastProbedUtc)</td>
+                </tr>
+            }
+            </tbody>
+        </table>
+    }
+</div>
+
+@code {
+    [Parameter] public string DriverInstanceId { get; set; } = string.Empty;
+
+    private ModbusAutoProhibitionsResponse? _response;
+    private string? _error;
+    private bool _loading;
+    private DateTime? _lastRefreshed;
+
+    private async Task LoadAsync()
+    {
+        _loading = true;
+        _error = null;
+        try
+        {
+            _response = await Diagnostics.GetModbusAutoProhibitedRangesAsync(DriverInstanceId);
+            _lastRefreshed = DateTime.UtcNow;
+            if (_response is null)
+                _error = $"Server reports driver '{DriverInstanceId}' is not present or is not a Modbus driver.";
+        }
+        catch (Exception ex)
+        {
+            _error = $"Fetch failed: {ex.Message}";
+        }
+        finally
+        {
+            _loading = false;
+        }
+    }
+
+    private static string FormatTimeSince(DateTime utc)
+    {
+        var span = DateTime.UtcNow - utc;
+        if (span.TotalSeconds < 60) return $"{(int)span.TotalSeconds}s ago";
+        if (span.TotalMinutes < 60) return $"{(int)span.TotalMinutes}m ago";
+        if (span.TotalHours < 24) return $"{(int)span.TotalHours}h ago";
+        return $"{(int)span.TotalDays}d ago";
+    }
+}

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

@@ -41,10 +41,20 @@ builder.Services.AddDbContext<OtOpcUaConfigDbContext>(opt =>
 builder.Services.AddScoped<ClusterService>();
 builder.Services.AddScoped<GenerationService>();
 builder.Services.AddScoped<EquipmentService>();
+builder.Services.AddScoped<TagService>();
 builder.Services.AddScoped<UnsService>();
 builder.Services.AddScoped<NamespaceService>();
 builder.Services.AddScoped<DriverInstanceService>();
 builder.Services.AddScoped<FocasDriverDetailService>();
+
+// #154 — Server diagnostics client. Default base URL points at the same machine's
+// HealthEndpointsHost (loopback :4841); deployments with remote Servers set
+// "DriverDiagnostics:ServerBaseUrl" in appsettings.json.
+builder.Services.AddHttpClient<DriverDiagnosticsClient>(client =>
+{
+    var baseUrl = builder.Configuration["DriverDiagnostics:ServerBaseUrl"] ?? "http://localhost:4841/";
+    client.BaseAddress = new Uri(baseUrl);
+});
 builder.Services.AddScoped<NodeAclService>();
 builder.Services.AddScoped<PermissionProbeService>();
 builder.Services.AddScoped<AclChangeNotifier>();

src/ZB.MOM.WW.OtOpcUa.Admin/Services/DriverDiagnosticsClient.cs

@@ -0,0 +1,61 @@
+namespace ZB.MOM.WW.OtOpcUa.Admin.Services;
+
+/// <summary>
+///     #154 — Admin-side client for the Server's driver-diagnostics HTTP endpoints. Wraps
+///     <see cref="HttpClient"/> so Blazor pages can fetch per-driver runtime state from a
+///     remote Server process. The base URL is configured at registration time
+///     (typically read from <c>appsettings.json</c> at startup).
+/// </summary>
+/// <remarks>
+///     One client instance per Server endpoint. Multi-server deployments register multiple
+///     keyed clients. Errors propagate as exceptions; pages catch and surface to the
+///     operator rather than swallowing.
+/// </remarks>
+public sealed class DriverDiagnosticsClient
+{
+    private readonly HttpClient _http;
+
+    public DriverDiagnosticsClient(HttpClient http) => _http = http;
+
+    /// <summary>
+    ///     Fetch the current Modbus auto-prohibition list for the named driver instance.
+    ///     Returns null when the Server reports the driver doesn't exist or isn't a Modbus
+    ///     driver. Throws on transport / serialization failures.
+    /// </summary>
+    public async Task<ModbusAutoProhibitionsResponse?> GetModbusAutoProhibitedRangesAsync(
+        string driverInstanceId, CancellationToken ct = default)
+    {
+        var resp = await _http.GetAsync(
+            $"/diagnostics/drivers/{Uri.EscapeDataString(driverInstanceId)}/modbus/auto-prohibited", ct)
+            .ConfigureAwait(false);
+
+        if (resp.StatusCode is System.Net.HttpStatusCode.NotFound or System.Net.HttpStatusCode.BadRequest)
+            return null;
+
+        resp.EnsureSuccessStatusCode();
+        return await resp.Content.ReadFromJsonAsync<ModbusAutoProhibitionsResponse>(cancellationToken: ct).ConfigureAwait(false);
+    }
+}
+
+/// <summary>
+///     Server response shape for the Modbus auto-prohibition diagnostic. Mirrors the JSON the
+///     <c>HealthEndpointsHost</c> serialises; fields are flat strings/numbers so the
+///     Admin-side client doesn't take a dependency on the Driver.Modbus assembly's
+///     <c>ModbusAutoProhibition</c> record.
+/// </summary>
+public sealed class ModbusAutoProhibitionsResponse
+{
+    public string DriverInstanceId { get; set; } = string.Empty;
+    public int Count { get; set; }
+    public List<ModbusAutoProhibitionRow> Ranges { get; set; } = new();
+}
+
+public sealed class ModbusAutoProhibitionRow
+{
+    public byte UnitId { get; set; }
+    public string Region { get; set; } = string.Empty;
+    public ushort StartAddress { get; set; }
+    public ushort EndAddress { get; set; }
+    public DateTime LastProbedUtc { get; set; }
+    public bool BisectionPending { get; set; }
+}

src/ZB.MOM.WW.OtOpcUa.Admin/Services/TagService.cs

@@ -0,0 +1,71 @@
+using Microsoft.EntityFrameworkCore;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+
+namespace ZB.MOM.WW.OtOpcUa.Admin.Services;
+
+/// <summary>
+///     #155 — Tag CRUD scoped to a draft generation. Tags are the canonical signal definitions
+///     (one row per OPC UA variable) the Server materialises into the address space at startup.
+///     Mirrors the shape of <see cref="EquipmentService"/>; writes are restricted to draft
+///     generations only (published generations are immutable per the validation pipeline).
+/// </summary>
+public sealed class TagService(OtOpcUaConfigDbContext db)
+{
+    /// <summary>Lists all tags in a generation, ordered by name. Optional driver / equipment filter.</summary>
+    public Task<List<Tag>> ListAsync(long generationId,
+        string? driverInstanceId = null,
+        string? equipmentId = null,
+        CancellationToken ct = default)
+    {
+        var query = db.Tags.AsNoTracking().Where(t => t.GenerationId == generationId);
+        if (!string.IsNullOrWhiteSpace(driverInstanceId))
+            query = query.Where(t => t.DriverInstanceId == driverInstanceId);
+        if (!string.IsNullOrWhiteSpace(equipmentId))
+            query = query.Where(t => t.EquipmentId == equipmentId);
+        return query.OrderBy(t => t.Name).ToListAsync(ct);
+    }
+
+    /// <summary>
+    ///     Creates a new tag row in the given draft. TagId is auto-derived as a GUID — the
+    ///     human-friendly Name is the user-facing identifier.
+    /// </summary>
+    public async Task<Tag> CreateAsync(long draftId, Tag input, CancellationToken ct)
+    {
+        input.GenerationId = draftId;
+        if (string.IsNullOrWhiteSpace(input.TagId))
+            input.TagId = Guid.NewGuid().ToString("N");
+        db.Tags.Add(input);
+        await db.SaveChangesAsync(ct);
+        return input;
+    }
+
+    public async Task UpdateAsync(Tag updated, CancellationToken ct)
+    {
+        var existing = await db.Tags
+            .FirstOrDefaultAsync(t => t.TagRowId == updated.TagRowId, ct)
+            ?? throw new InvalidOperationException($"Tag row {updated.TagRowId} not found");
+
+        // Editable fields. TagId / GenerationId are immutable; the Validation pipeline rejects
+        // changes that would break referential integrity (sp_ValidateDraft per decision #110).
+        existing.Name = updated.Name;
+        existing.DriverInstanceId = updated.DriverInstanceId;
+        existing.DeviceId = updated.DeviceId;
+        existing.EquipmentId = updated.EquipmentId;
+        existing.FolderPath = updated.FolderPath;
+        existing.DataType = updated.DataType;
+        existing.AccessLevel = updated.AccessLevel;
+        existing.WriteIdempotent = updated.WriteIdempotent;
+        existing.PollGroupId = updated.PollGroupId;
+        existing.TagConfig = updated.TagConfig;
+        await db.SaveChangesAsync(ct);
+    }
+
+    public async Task DeleteAsync(Guid tagRowId, CancellationToken ct)
+    {
+        var existing = await db.Tags.FirstOrDefaultAsync(t => t.TagRowId == tagRowId, ct);
+        if (existing is null) return;
+        db.Tags.Remove(existing);
+        await db.SaveChangesAsync(ct);
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/HistorianClusterNodeState.cs

@@ -0,0 +1,19 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+/// <summary>
+///     Point-in-time state of a single historian cluster node, included inside
+///     <see cref="HistorianHealthSnapshot.Nodes"/> when the backend is clustered.
+/// </summary>
+/// <param name="Name">Node identifier — backend-specific (typically a hostname).</param>
+/// <param name="IsHealthy">True when the node is currently considered usable for reads.</param>
+/// <param name="CooldownUntil">When the next retry against an unhealthy node is allowed; null when no cooldown is active.</param>
+/// <param name="FailureCount">Consecutive failures observed against this node since the last success.</param>
+/// <param name="LastError">Diagnostic text from the last failure against this node; null when no failures.</param>
+/// <param name="LastFailureTime">UTC of the last failure against this node; null when no failures.</param>
+public sealed record HistorianClusterNodeState(
+    string Name,
+    bool IsHealthy,
+    DateTime? CooldownUntil,
+    int FailureCount,
+    string? LastError,
+    DateTime? LastFailureTime);

src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/HistorianHealthSnapshot.cs

@@ -0,0 +1,32 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+/// <summary>
+///     Point-in-time runtime health of a historian data source. Returned by
+///     <see cref="IHistorianDataSource.GetHealthSnapshot"/> and projected onto the
+///     server status dashboard.
+/// </summary>
+/// <param name="TotalQueries">Lifetime count of read calls received.</param>
+/// <param name="TotalSuccesses">Subset of <paramref name="TotalQueries"/> that completed without error.</param>
+/// <param name="TotalFailures">Subset of <paramref name="TotalQueries"/> that ended in error.</param>
+/// <param name="ConsecutiveFailures">Failures since the last success — non-zero means the source is currently degraded.</param>
+/// <param name="LastSuccessTime">UTC of the most recent successful read; null if none yet.</param>
+/// <param name="LastFailureTime">UTC of the most recent failed read; null if none yet.</param>
+/// <param name="LastError">Diagnostic text from the most recent failure; null when no failures recorded.</param>
+/// <param name="ProcessConnectionOpen">True when the source's process-data connection is currently established.</param>
+/// <param name="EventConnectionOpen">True when the source's event-data connection is currently established. Some backends share one connection — implementations may report the same value here as <paramref name="ProcessConnectionOpen"/>.</param>
+/// <param name="ActiveProcessNode">Cluster node currently serving process reads; null when no node is active or the backend is non-clustered.</param>
+/// <param name="ActiveEventNode">Cluster node currently serving event reads; null when no node is active or the backend is non-clustered.</param>
+/// <param name="Nodes">Per-cluster-node state. Empty when the backend is non-clustered.</param>
+public sealed record HistorianHealthSnapshot(
+    long TotalQueries,
+    long TotalSuccesses,
+    long TotalFailures,
+    int ConsecutiveFailures,
+    DateTime? LastSuccessTime,
+    DateTime? LastFailureTime,
+    string? LastError,
+    bool ProcessConnectionOpen,
+    bool EventConnectionOpen,
+    string? ActiveProcessNode,
+    string? ActiveEventNode,
+    IReadOnlyList<HistorianClusterNodeState> Nodes);

src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/IHistorianDataSource.cs

@@ -0,0 +1,74 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+/// <summary>
+///     Server-side historian data source. Registered with the server's history router
+///     and resolved per OPC UA namespace, independent of any driver's lifecycle.
+/// </summary>
+/// <remarks>
+///     Distinct from <see cref="IHistoryProvider"/>:
+///     <list type="bullet">
+///       <item><see cref="IHistoryProvider"/> is a *driver capability* — the server
+///         dispatches to it via the driver instance.</item>
+///       <item><see cref="IHistorianDataSource"/> is a *server registration* — the
+///         server resolves it via namespace and calls it directly, so a single
+///         historian (e.g. Wonderware) can serve many drivers' nodes, and drivers can
+///         restart without dropping history availability.</item>
+///     </list>
+///     All values returned use the shared <see cref="DataValueSnapshot"/> /
+///     <see cref="HistoricalEvent"/> shapes; backend-specific quality / type encodings
+///     are translated to OPC UA <c>StatusCode</c> uints inside the data source.
+/// </remarks>
+public interface IHistorianDataSource : IDisposable
+{
+    /// <summary>
+    ///     Read raw historical samples for a single tag over a time range.
+    /// </summary>
+    Task<HistoryReadResult> ReadRawAsync(
+        string fullReference,
+        DateTime startUtc,
+        DateTime endUtc,
+        uint maxValuesPerNode,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Read processed (interval-bucketed) samples — average / min / max / count / etc.
+    ///     A bucket with no source data returns a sample whose
+    ///     <see cref="DataValueSnapshot.StatusCode"/> indicates BadNoData.
+    /// </summary>
+    Task<HistoryReadResult> ReadProcessedAsync(
+        string fullReference,
+        DateTime startUtc,
+        DateTime endUtc,
+        TimeSpan interval,
+        HistoryAggregateType aggregate,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Read one sample per requested timestamp — OPC UA HistoryReadAtTime service.
+    ///     Implementations interpolate or return prior-boundary samples per their
+    ///     backend's policy. The returned list MUST be the same length and order as
+    ///     <paramref name="timestampsUtc"/>; gaps are returned as Bad-quality snapshots.
+    /// </summary>
+    Task<HistoryReadResult> ReadAtTimeAsync(
+        string fullReference,
+        IReadOnlyList<DateTime> timestampsUtc,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Read historical alarm / event records — OPC UA HistoryReadEvents service.
+    ///     Distinct from any live event stream; sources here come from the historian's
+    ///     event log. <paramref name="sourceName"/> is null to return all sources.
+    /// </summary>
+    Task<HistoricalEventsResult> ReadEventsAsync(
+        string? sourceName,
+        DateTime startUtc,
+        DateTime endUtc,
+        int maxEvents,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Point-in-time health snapshot for diagnostics and dashboards. Pure
+    ///     observation; never blocks on backend I/O.
+    /// </summary>
+    HistorianHealthSnapshot GetHealthSnapshot();
+}

src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IAddressSpaceBuilder.cs

@@ -62,10 +62,41 @@ public interface IVariableHandle
 /// <param name="SourceName">Human-readable alarm name used for the <c>SourceName</c> event field.</param>
 /// <param name="InitialSeverity">Severity at address-space build time; updates arrive via <see cref="IAlarmConditionSink"/>.</param>
 /// <param name="InitialDescription">Initial description; updates arrive via <see cref="IAlarmConditionSink"/>.</param>
+/// <param name="InAlarmRef">
+///     Driver-side full reference for the boolean attribute that toggles when the
+///     alarm condition becomes active. Consumed by the server-level alarm-condition
+///     service to subscribe to active/inactive transitions. Null when the driver
+///     reports alarm transitions through some other channel.
+/// </param>
+/// <param name="PriorityRef">
+///     Driver-side full reference for the integer attribute carrying the alarm's
+///     current priority / severity. Live updates flow through the same subscription
+///     pipeline as <paramref name="InAlarmRef"/>. Null when the driver does not
+///     expose live priority changes.
+/// </param>
+/// <param name="DescAttrNameRef">
+///     Driver-side full reference for the string attribute carrying the human-readable
+///     description / message. Null when the driver does not expose a live description.
+/// </param>
+/// <param name="AckedRef">
+///     Driver-side full reference for the boolean attribute that toggles when the
+///     alarm is acknowledged. Null when acknowledgement is not observable on the
+///     driver side.
+/// </param>
+/// <param name="AckMsgWriteRef">
+///     Driver-side full reference the server writes to acknowledge the condition,
+///     typically the alarm's <c>.AckMsg</c> attribute. Null when the driver does not
+///     accept acknowledgement writes (or routes them through a separate API).
+/// </param>
 public sealed record AlarmConditionInfo(
     string SourceName,
     AlarmSeverity InitialSeverity,
-    string? InitialDescription);
+    string? InitialDescription,
+    string? InAlarmRef = null,
+    string? PriorityRef = null,
+    string? DescAttrNameRef = null,
+    string? AckedRef = null,
+    string? AckMsgWriteRef = null);
 
 /// <summary>
 ///     Sink a concrete address-space builder returns from <see cref="IVariableHandle.MarkAsAlarmCondition"/>.

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host/Backend/MxAccessGalaxyBackend.cs

@@ -6,7 +6,7 @@ using System.Threading.Tasks;
 using MessagePack;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Alarms;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Stability;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;

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

@@ -4,7 +4,7 @@ using System.Threading;
 using Serilog;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Ipc;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Sta;

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

@@ -28,6 +28,10 @@
 
     <ItemGroup>
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.csproj"/>
+        <!-- PR 3.2: Historian SDK code lifted to the Wonderware sidecar. Galaxy.Host still
+             consumes the historian types (MxAccessGalaxyBackend, Program) until phase 7,
+             so reference the sidecar project to keep building. -->
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware\ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.csproj"/>
     </ItemGroup>
 
     <ItemGroup>
@@ -39,34 +43,6 @@
             <HintPath>..\..\lib\ArchestrA.MxAccess.dll</HintPath>
             <Private>true</Private>
         </Reference>
-        <!-- Wonderware Historian SDK — consumed by Backend/Historian/ for HistoryReadAsync.
-             Previously lived in the v1 Historian.Aveva plugin; folded into Driver.Galaxy.Host
-             for PR #5 because this host is already Galaxy-specific. -->
-        <Reference Include="aahClientManaged">
-            <HintPath>..\..\lib\aahClientManaged.dll</HintPath>
-            <EmbedInteropTypes>false</EmbedInteropTypes>
-        </Reference>
-        <Reference Include="aahClientCommon">
-            <HintPath>..\..\lib\aahClientCommon.dll</HintPath>
-            <EmbedInteropTypes>false</EmbedInteropTypes>
-        </Reference>
-    </ItemGroup>
-
-    <ItemGroup>
-        <!-- Historian SDK native and satellite DLLs — staged beside the host exe so the
-             aahClientManaged wrapper can P/Invoke into them without an AssemblyResolve hook. -->
-        <None Include="..\..\lib\aahClient.dll">
-            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-        </None>
-        <None Include="..\..\lib\Historian.CBE.dll">
-            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-        </None>
-        <None Include="..\..\lib\Historian.DPAPI.dll">
-            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-        </None>
-        <None Include="..\..\lib\ArchestrA.CloudHistorian.Contract.dll">
-            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-        </None>
     </ItemGroup>
 
     <ItemGroup>

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianClusterEndpointPicker.cs

@@ -2,7 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     Thread-safe, pure-logic endpoint picker for the Wonderware Historian cluster. Tracks which

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianClusterNodeState.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     Point-in-time state of a single historian cluster node. One entry per configured node

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianConfiguration.cs

@@ -1,6 +1,6 @@
 using System.Collections.Generic;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     Wonderware Historian SDK configuration. Populated from environment variables at Host

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianDataSource.cs

@@ -6,7 +6,7 @@ using System.Threading.Tasks;
 using ArchestrA;
 using Serilog;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     Reads historical data from the Wonderware Historian via the aahClientManaged SDK.

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianEventDto.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     SDK-free representation of a Historian event record. Prevents ArchestrA types from

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianHealthSnapshot.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Collections.Generic;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     Point-in-time runtime health of the historian subsystem — consumed by the status dashboard

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianQualityMapper.cs

@@ -1,4 +1,4 @@
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 
 /// <summary>
 ///     Maps a raw OPC DA quality byte (as returned by Wonderware Historian's <c>OpcQuality</c>)

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianSample.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     OPC-UA-free representation of a single historical data point. The Host returns these

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/IHistorianConnectionFactory.cs

@@ -2,7 +2,7 @@ using System;
 using System.Threading;
 using ArchestrA;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     Creates and opens Historian SDK connections. Extracted so tests can inject fakes that

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/IHistorianDataSource.cs

@@ -3,7 +3,7 @@ using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 
-namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
 {
     /// <summary>
     ///     OPC-UA-free surface for the Wonderware Historian subsystem inside Galaxy.Host.

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Ipc/Contracts.cs

@@ -0,0 +1,168 @@
+using System;
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+// ============================================================================
+// Wire DTOs for the sidecar pipe protocol. The sidecar speaks its own legacy
+// shape (List<HistorianSample> etc.) — the .NET 10 client (PR 3.4) translates
+// to / from Core.Abstractions.DataValueSnapshot + HistoricalEvent.
+//
+// Timestamps cross the wire as DateTime ticks (long) to dodge MessagePack's
+// DateTime kind/timezone quirks; both sides convert with DateTime(ticks, Utc).
+// ============================================================================
+
+/// <summary>Single historical data point. Quality is the raw OPC DA byte; client maps to OPC UA StatusCode.</summary>
+[MessagePackObject]
+public sealed class HistorianSampleDto
+{
+    /// <summary>MessagePack-serialized value bytes. Client deserializes per the tag's mx_data_type.</summary>
+    [Key(0)] public byte[]? ValueBytes { get; set; }
+
+    /// <summary>Raw OPC DA quality byte from the historian SDK (low 8 bits of OpcQuality).</summary>
+    [Key(1)] public byte Quality { get; set; }
+
+    [Key(2)] public long TimestampUtcTicks { get; set; }
+}
+
+/// <summary>Aggregate bucket; <c>Value</c> is null when the aggregate is unavailable for the bucket.</summary>
+[MessagePackObject]
+public sealed class HistorianAggregateSampleDto
+{
+    [Key(0)] public double? Value { get; set; }
+    [Key(1)] public long TimestampUtcTicks { get; set; }
+}
+
+/// <summary>Historian event row.</summary>
+[MessagePackObject]
+public sealed class HistorianEventDto
+{
+    [Key(0)] public string EventId { get; set; } = string.Empty;
+    [Key(1)] public string? Source { get; set; }
+    [Key(2)] public long EventTimeUtcTicks { get; set; }
+    [Key(3)] public long ReceivedTimeUtcTicks { get; set; }
+    [Key(4)] public string? DisplayText { get; set; }
+    [Key(5)] public ushort Severity { get; set; }
+}
+
+/// <summary>Alarm event to persist back into the historian event store.</summary>
+[MessagePackObject]
+public sealed class AlarmHistorianEventDto
+{
+    [Key(0)] public string EventId { get; set; } = string.Empty;
+    [Key(1)] public string SourceName { get; set; } = string.Empty;
+    [Key(2)] public string? ConditionId { get; set; }
+    [Key(3)] public string AlarmType { get; set; } = string.Empty;
+    [Key(4)] public string? Message { get; set; }
+    [Key(5)] public ushort Severity { get; set; }
+    [Key(6)] public long EventTimeUtcTicks { get; set; }
+    [Key(7)] public string? AckComment { get; set; }
+}
+
+// ===== Read Raw =====
+
+[MessagePackObject]
+public sealed class ReadRawRequest
+{
+    [Key(0)] public string TagName { get; set; } = string.Empty;
+    [Key(1)] public long StartUtcTicks { get; set; }
+    [Key(2)] public long EndUtcTicks { get; set; }
+    [Key(3)] public int MaxValues { get; set; }
+    [Key(4)] public string CorrelationId { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class ReadRawReply
+{
+    [Key(0)] public string CorrelationId { get; set; } = string.Empty;
+    [Key(1)] public bool Success { get; set; }
+    [Key(2)] public string? Error { get; set; }
+    [Key(3)] public HistorianSampleDto[] Samples { get; set; } = Array.Empty<HistorianSampleDto>();
+}
+
+// ===== Read Processed =====
+
+[MessagePackObject]
+public sealed class ReadProcessedRequest
+{
+    [Key(0)] public string TagName { get; set; } = string.Empty;
+    [Key(1)] public long StartUtcTicks { get; set; }
+    [Key(2)] public long EndUtcTicks { get; set; }
+    [Key(3)] public double IntervalMs { get; set; }
+
+    /// <summary>
+    ///     Wonderware AnalogSummary column name: "Average", "Minimum", "Maximum", "ValueCount".
+    ///     The .NET 10 client maps OPC UA aggregate enum → column.
+    /// </summary>
+    [Key(4)] public string AggregateColumn { get; set; } = string.Empty;
+    [Key(5)] public string CorrelationId { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class ReadProcessedReply
+{
+    [Key(0)] public string CorrelationId { get; set; } = string.Empty;
+    [Key(1)] public bool Success { get; set; }
+    [Key(2)] public string? Error { get; set; }
+    [Key(3)] public HistorianAggregateSampleDto[] Buckets { get; set; } = Array.Empty<HistorianAggregateSampleDto>();
+}
+
+// ===== Read At-Time =====
+
+[MessagePackObject]
+public sealed class ReadAtTimeRequest
+{
+    [Key(0)] public string TagName { get; set; } = string.Empty;
+    [Key(1)] public long[] TimestampsUtcTicks { get; set; } = Array.Empty<long>();
+    [Key(2)] public string CorrelationId { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class ReadAtTimeReply
+{
+    [Key(0)] public string CorrelationId { get; set; } = string.Empty;
+    [Key(1)] public bool Success { get; set; }
+    [Key(2)] public string? Error { get; set; }
+    [Key(3)] public HistorianSampleDto[] Samples { get; set; } = Array.Empty<HistorianSampleDto>();
+}
+
+// ===== Read Events =====
+
+[MessagePackObject]
+public sealed class ReadEventsRequest
+{
+    [Key(0)] public string? SourceName { get; set; }
+    [Key(1)] public long StartUtcTicks { get; set; }
+    [Key(2)] public long EndUtcTicks { get; set; }
+    [Key(3)] public int MaxEvents { get; set; }
+    [Key(4)] public string CorrelationId { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class ReadEventsReply
+{
+    [Key(0)] public string CorrelationId { get; set; } = string.Empty;
+    [Key(1)] public bool Success { get; set; }
+    [Key(2)] public string? Error { get; set; }
+    [Key(3)] public HistorianEventDto[] Events { get; set; } = Array.Empty<HistorianEventDto>();
+}
+
+// ===== Write Alarm Events =====
+
+[MessagePackObject]
+public sealed class WriteAlarmEventsRequest
+{
+    [Key(0)] public AlarmHistorianEventDto[] Events { get; set; } = Array.Empty<AlarmHistorianEventDto>();
+    [Key(1)] public string CorrelationId { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class WriteAlarmEventsReply
+{
+    [Key(0)] public string CorrelationId { get; set; } = string.Empty;
+    [Key(1)] public bool Success { get; set; }
+    [Key(2)] public string? Error { get; set; }
+
+    /// <summary>Per-event success flag, parallel to <see cref="WriteAlarmEventsRequest.Events"/>.</summary>
+    [Key(3)] public bool[] PerEventOk { get; set; } = Array.Empty<bool>();
+}

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Ipc/FrameReader.cs

@@ -0,0 +1,68 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+/// <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. Mirror of
+///     Driver.Galaxy.Shared.FrameReader; sidecar carries its own copy so the deletion of
+///     Galaxy.Shared in PR 7.2 doesn't reach the sidecar.
+/// </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<(MessageKind Kind, byte[] Body)?> ReadFrameAsync(CancellationToken ct)
+    {
+        var lengthPrefix = new byte[Framing.LengthPrefixSize];
+        if (!await ReadExactAsync(lengthPrefix, ct).ConfigureAwait(false))
+            return null; // clean EOF on frame boundary
+
+        var length = (lengthPrefix[0] << 24) | (lengthPrefix[1] << 16) | (lengthPrefix[2] << 8) | lengthPrefix[3];
+        if (length < 0 || length > Framing.MaxFrameBodyBytes)
+            throw new InvalidDataException($"Sidecar IPC frame length {length} out of range.");
+
+        var kindByte = _stream.ReadByte();
+        if (kindByte < 0) throw new EndOfStreamException("EOF after length prefix, before kind byte.");
+
+        var body = new byte[length];
+        if (!await ReadExactAsync(body, ct).ConfigureAwait(false))
+            throw new EndOfStreamException("EOF mid-frame.");
+
+        return ((MessageKind)(byte)kindByte, body);
+    }
+
+    public static T Deserialize<T>(byte[] body) => MessagePackSerializer.Deserialize<T>(body);
+
+    private async Task<bool> ReadExactAsync(byte[] buffer, CancellationToken ct)
+    {
+        var offset = 0;
+        while (offset < buffer.Length)
+        {
+            var read = await _stream.ReadAsync(buffer, offset, buffer.Length - offset, ct).ConfigureAwait(false);
+            if (read == 0)
+            {
+                if (offset == 0) return false;
+                throw new EndOfStreamException($"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.Historian.Wonderware/Ipc/FrameWriter.cs

@@ -0,0 +1,57 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+/// <summary>
+///     Writes length-prefixed, kind-tagged MessagePack frames to a stream. Thread-safe via
+///     <see cref="SemaphoreSlim"/> so concurrent producers (heartbeat + reply paths) get
+///     serialized writes. Mirror of Driver.Galaxy.Shared.FrameWriter; sidecar carries its
+///     own copy.
+/// </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>(MessageKind kind, T message, CancellationToken ct)
+    {
+        var body = MessagePackSerializer.Serialize(message, cancellationToken: ct);
+        if (body.Length > Framing.MaxFrameBodyBytes)
+            throw new InvalidOperationException(
+                $"Sidecar IPC frame body {body.Length} exceeds {Framing.MaxFrameBodyBytes} byte cap.");
+
+        var lengthPrefix = new byte[Framing.LengthPrefixSize];
+        // Big-endian — easy to read in hex dumps.
+        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.Historian.Wonderware/Ipc/Framing.cs

@@ -0,0 +1,48 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+/// <summary>
+///     Length-prefixed framing constants for the Wonderware historian sidecar pipe protocol.
+///     Each frame on the wire 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.
+/// </summary>
+/// <remarks>
+///     Mirrors the Galaxy.Shared framing exactly so the same FrameReader/FrameWriter pattern
+///     works on both sides. The sidecar's protocol is independent — both the .NET 4.8 server
+///     side and the .NET 10 client (PR 3.4) carry their own copies of these constants and
+///     stay in sync via the round-trip test matrix.
+/// </remarks>
+public static class Framing
+{
+    public const int LengthPrefixSize = 4;
+    public const int KindByteSize = 1;
+
+    /// <summary>16 MiB cap protects the receiver from a hostile or buggy peer.</summary>
+    public const int MaxFrameBodyBytes = 16 * 1024 * 1024;
+}
+
+/// <summary>
+///     Wire identifier for each historian sidecar message. Values are stable — never reorder;
+///     append new contracts at the end. The .NET 10 client and the .NET 4.8 sidecar must
+///     agree on every value here.
+/// </summary>
+public enum MessageKind : byte
+{
+    Hello                       = 0x01,
+    HelloAck                    = 0x02,
+
+    ReadRawRequest              = 0x10,
+    ReadRawReply                = 0x11,
+
+    ReadProcessedRequest        = 0x12,
+    ReadProcessedReply          = 0x13,
+
+    ReadAtTimeRequest           = 0x14,
+    ReadAtTimeReply             = 0x15,
+
+    ReadEventsRequest           = 0x16,
+    ReadEventsReply             = 0x17,
+
+    WriteAlarmEventsRequest     = 0x20,
+    WriteAlarmEventsReply       = 0x21,
+}

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Ipc/Hello.cs

@@ -0,0 +1,32 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+/// <summary>
+///     First frame of every connection. Advertises the sidecar protocol version and the
+///     per-process shared secret the supervisor passed at spawn time.
+/// </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 against the value the supervisor passed at spawn time.</summary>
+    [Key(3)] public string SharedSecret { get; set; } = string.Empty;
+}
+
+[MessagePackObject]
+public sealed class HelloAck
+{
+    [Key(0)] public int ProtocolMajor { get; set; } = Hello.CurrentMajor;
+    [Key(1)] public int ProtocolMinor { get; set; } = Hello.CurrentMinor;
+
+    [Key(2)] public bool Accepted { get; set; }
+    [Key(3)] public string? RejectReason { get; set; }
+    [Key(4)] public string HostName { get; set; } = string.Empty;
+}

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Ipc/HistorianFrameHandler.cs

@@ -0,0 +1,250 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+/// <summary>
+///     Sidecar-side dispatcher. Each post-Hello frame routes by <see cref="MessageKind"/> to
+///     the right historian operation and the result frame is written back through the same
+///     pipe. Per-call exceptions are caught and surfaced as <c>Success=false, Error=...</c>
+///     replies so a single bad request doesn't kill the connection.
+/// </summary>
+public sealed class HistorianFrameHandler : IFrameHandler
+{
+    private readonly IHistorianDataSource _historian;
+    private readonly IAlarmEventWriter? _alarmWriter;
+    private readonly ILogger _logger;
+
+    public HistorianFrameHandler(
+        IHistorianDataSource historian,
+        ILogger logger,
+        IAlarmEventWriter? alarmWriter = null)
+    {
+        _historian = historian ?? throw new ArgumentNullException(nameof(historian));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _alarmWriter = alarmWriter;
+    }
+
+    public Task HandleAsync(MessageKind kind, byte[] body, FrameWriter writer, CancellationToken ct)
+        => kind switch
+        {
+            MessageKind.ReadRawRequest => HandleReadRawAsync(body, writer, ct),
+            MessageKind.ReadProcessedRequest => HandleReadProcessedAsync(body, writer, ct),
+            MessageKind.ReadAtTimeRequest => HandleReadAtTimeAsync(body, writer, ct),
+            MessageKind.ReadEventsRequest => HandleReadEventsAsync(body, writer, ct),
+            MessageKind.WriteAlarmEventsRequest => HandleWriteAlarmEventsAsync(body, writer, ct),
+            _ => UnknownAsync(kind),
+        };
+
+    private Task UnknownAsync(MessageKind kind)
+    {
+        _logger.Warning("Sidecar received unsupported frame kind {Kind}; dropping", kind);
+        return Task.CompletedTask;
+    }
+
+    private async Task HandleReadRawAsync(byte[] body, FrameWriter writer, CancellationToken ct)
+    {
+        var req = MessagePackSerializer.Deserialize<ReadRawRequest>(body);
+        var reply = new ReadRawReply { CorrelationId = req.CorrelationId };
+        try
+        {
+            var samples = await _historian.ReadRawAsync(
+                req.TagName,
+                new DateTime(req.StartUtcTicks, DateTimeKind.Utc),
+                new DateTime(req.EndUtcTicks, DateTimeKind.Utc),
+                req.MaxValues,
+                ct).ConfigureAwait(false);
+
+            reply.Success = true;
+            reply.Samples = ToWire(samples);
+        }
+        catch (Exception ex)
+        {
+            _logger.Warning(ex, "Sidecar ReadRaw failed for {Tag}", req.TagName);
+            reply.Success = false;
+            reply.Error = ex.Message;
+        }
+
+        await writer.WriteAsync(MessageKind.ReadRawReply, reply, ct).ConfigureAwait(false);
+    }
+
+    private async Task HandleReadProcessedAsync(byte[] body, FrameWriter writer, CancellationToken ct)
+    {
+        var req = MessagePackSerializer.Deserialize<ReadProcessedRequest>(body);
+        var reply = new ReadProcessedReply { CorrelationId = req.CorrelationId };
+        try
+        {
+            var buckets = await _historian.ReadAggregateAsync(
+                req.TagName,
+                new DateTime(req.StartUtcTicks, DateTimeKind.Utc),
+                new DateTime(req.EndUtcTicks, DateTimeKind.Utc),
+                req.IntervalMs,
+                req.AggregateColumn,
+                ct).ConfigureAwait(false);
+
+            reply.Success = true;
+            reply.Buckets = ToWire(buckets);
+        }
+        catch (Exception ex)
+        {
+            _logger.Warning(ex, "Sidecar ReadProcessed failed for {Tag}", req.TagName);
+            reply.Success = false;
+            reply.Error = ex.Message;
+        }
+
+        await writer.WriteAsync(MessageKind.ReadProcessedReply, reply, ct).ConfigureAwait(false);
+    }
+
+    private async Task HandleReadAtTimeAsync(byte[] body, FrameWriter writer, CancellationToken ct)
+    {
+        var req = MessagePackSerializer.Deserialize<ReadAtTimeRequest>(body);
+        var reply = new ReadAtTimeReply { CorrelationId = req.CorrelationId };
+        try
+        {
+            var timestamps = new DateTime[req.TimestampsUtcTicks.Length];
+            for (var i = 0; i < timestamps.Length; i++)
+                timestamps[i] = new DateTime(req.TimestampsUtcTicks[i], DateTimeKind.Utc);
+
+            var samples = await _historian.ReadAtTimeAsync(req.TagName, timestamps, ct).ConfigureAwait(false);
+            reply.Success = true;
+            reply.Samples = ToWire(samples);
+        }
+        catch (Exception ex)
+        {
+            _logger.Warning(ex, "Sidecar ReadAtTime failed for {Tag}", req.TagName);
+            reply.Success = false;
+            reply.Error = ex.Message;
+        }
+
+        await writer.WriteAsync(MessageKind.ReadAtTimeReply, reply, ct).ConfigureAwait(false);
+    }
+
+    private async Task HandleReadEventsAsync(byte[] body, FrameWriter writer, CancellationToken ct)
+    {
+        var req = MessagePackSerializer.Deserialize<ReadEventsRequest>(body);
+        var reply = new ReadEventsReply { CorrelationId = req.CorrelationId };
+        try
+        {
+            var events = await _historian.ReadEventsAsync(
+                req.SourceName,
+                new DateTime(req.StartUtcTicks, DateTimeKind.Utc),
+                new DateTime(req.EndUtcTicks, DateTimeKind.Utc),
+                req.MaxEvents,
+                ct).ConfigureAwait(false);
+
+            reply.Success = true;
+            reply.Events = ToWire(events);
+        }
+        catch (Exception ex)
+        {
+            _logger.Warning(ex, "Sidecar ReadEvents failed for source {Source}", req.SourceName);
+            reply.Success = false;
+            reply.Error = ex.Message;
+        }
+
+        await writer.WriteAsync(MessageKind.ReadEventsReply, reply, ct).ConfigureAwait(false);
+    }
+
+    private async Task HandleWriteAlarmEventsAsync(byte[] body, FrameWriter writer, CancellationToken ct)
+    {
+        var req = MessagePackSerializer.Deserialize<WriteAlarmEventsRequest>(body);
+        var reply = new WriteAlarmEventsReply { CorrelationId = req.CorrelationId };
+
+        if (_alarmWriter is null)
+        {
+            reply.Success = false;
+            reply.Error = "Sidecar not configured with an alarm-event writer.";
+            reply.PerEventOk = new bool[req.Events.Length];
+            await writer.WriteAsync(MessageKind.WriteAlarmEventsReply, reply, ct).ConfigureAwait(false);
+            return;
+        }
+
+        try
+        {
+            var perEvent = await _alarmWriter.WriteAsync(req.Events, ct).ConfigureAwait(false);
+            reply.PerEventOk = perEvent;
+            reply.Success = true;
+            // Whole-batch Success stays true even when some events failed — per-event
+            // PerEventOk slots carry the granular result; the SQLite drain worker treats
+            // false slots as retry-please candidates.
+        }
+        catch (Exception ex)
+        {
+            _logger.Warning(ex, "Sidecar WriteAlarmEvents failed");
+            reply.Success = false;
+            reply.Error = ex.Message;
+            reply.PerEventOk = new bool[req.Events.Length];
+        }
+
+        await writer.WriteAsync(MessageKind.WriteAlarmEventsReply, reply, ct).ConfigureAwait(false);
+    }
+
+    private static HistorianSampleDto[] ToWire(List<HistorianSample> samples)
+    {
+        var dtos = new HistorianSampleDto[samples.Count];
+        for (var i = 0; i < samples.Count; i++)
+        {
+            var s = samples[i];
+            dtos[i] = new HistorianSampleDto
+            {
+                ValueBytes = s.Value is null ? null : MessagePackSerializer.Serialize(s.Value),
+                Quality = s.Quality,
+                TimestampUtcTicks = s.TimestampUtc.Ticks,
+            };
+        }
+        return dtos;
+    }
+
+    private static HistorianAggregateSampleDto[] ToWire(List<HistorianAggregateSample> samples)
+    {
+        var dtos = new HistorianAggregateSampleDto[samples.Count];
+        for (var i = 0; i < samples.Count; i++)
+        {
+            dtos[i] = new HistorianAggregateSampleDto
+            {
+                Value = samples[i].Value,
+                TimestampUtcTicks = samples[i].TimestampUtc.Ticks,
+            };
+        }
+        return dtos;
+    }
+
+    private static HistorianEventDto[] ToWire(List<Backend.HistorianEventDto> events)
+    {
+        var dtos = new HistorianEventDto[events.Count];
+        for (var i = 0; i < events.Count; i++)
+        {
+            var e = events[i];
+            dtos[i] = new HistorianEventDto
+            {
+                EventId = e.Id.ToString(),
+                Source = e.Source,
+                EventTimeUtcTicks = e.EventTime.Ticks,
+                ReceivedTimeUtcTicks = e.ReceivedTime.Ticks,
+                DisplayText = e.DisplayText,
+                Severity = e.Severity,
+            };
+        }
+        return dtos;
+    }
+}
+
+/// <summary>
+///     Strategy for persisting alarm events into the Wonderware Alarm &amp; Events log. PR 3.W
+///     supplies a real implementation that drives the aahClient SDK; PR 3.3 ships the
+///     contract + a default null implementation so the sidecar can boot without one.
+/// </summary>
+public interface IAlarmEventWriter
+{
+    /// <summary>
+    ///     Writes a batch of alarm events. Returns one boolean per input event indicating
+    ///     persisted vs. retry-please. The SQLite store-and-forward sink retries failed
+    ///     slots on the next drain tick.
+    /// </summary>
+    Task<bool[]> WriteAsync(AlarmHistorianEventDto[] events, CancellationToken cancellationToken);
+}

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Ipc/PipeAcl.cs

@@ -0,0 +1,36 @@
+using System;
+using System.IO.Pipes;
+using System.Security.AccessControl;
+using System.Security.Principal;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+/// <summary>
+///     Builds a strict <see cref="PipeSecurity"/> for the historian sidecar pipe — only the
+///     configured server-principal SID gets <c>ReadWrite | Synchronize</c>, LocalSystem is
+///     explicitly denied (unless it's the allowed principal itself), and the allowed SID owns
+///     the DACL. Mirrors the policy in Driver.Galaxy.Host's PipeAcl.
+/// </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);
+        if (allowedSid != localSystem)
+            security.AddAccessRule(new PipeAccessRule(localSystem, PipeAccessRights.FullControl, AccessControlType.Deny));
+
+        // Owner = allowed SID so the deny rules can't be removed without write-DACL rights.
+        security.SetOwner(allowedSid);
+
+        return security;
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Ipc/PipeServer.cs

@@ -0,0 +1,165 @@
+using System;
+using System.IO.Pipes;
+using System.Security.Principal;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using Serilog;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+/// <summary>
+///     Accepts one client connection at a time on a named pipe with the strict ACL from
+///     <see cref="PipeAcl"/>. Verifies the peer SID and the per-process shared secret before
+///     any frame is dispatched. Mirrors Driver.Galaxy.Host's PipeServer; the sidecar carries
+///     its own copy so the deletion of Galaxy.Host in PR 7.2 leaves the sidecar self-contained.
+/// </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));
+    }
+
+    /// <summary>
+    ///     Accepts one connection, performs Hello handshake, then dispatches frames to
+    ///     <paramref name="handler"/> until EOF or cancel. Returns when the client disconnects.
+    /// </summary>
+    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);
+
+            using var reader = new FrameReader(_current, leaveOpen: true);
+            using var writer = new FrameWriter(_current, leaveOpen: true);
+
+            // First frame must be Hello with the correct shared secret. Reading it before
+            // the caller-SID impersonation check satisfies Windows' ERROR_CANNOT_IMPERSONATE
+            // rule — ImpersonateNamedPipeClient fails until at least one frame has been read.
+            var first = await reader.ReadFrameAsync(linked.Token).ConfigureAwait(false);
+            if (first is null || first.Value.Kind != MessageKind.Hello)
+            {
+                _logger.Warning("Sidecar IPC first frame was not Hello; dropping");
+                return;
+            }
+
+            if (!VerifyCaller(_current, out var reason))
+            {
+                _logger.Warning("Sidecar IPC caller rejected: {Reason}", reason);
+                _current.Disconnect();
+                return;
+            }
+
+            var hello = MessagePackSerializer.Deserialize<Hello>(first.Value.Body);
+            if (!string.Equals(hello.SharedSecret, _sharedSecret, StringComparison.Ordinal))
+            {
+                await writer.WriteAsync(MessageKind.HelloAck,
+                    new HelloAck { Accepted = false, RejectReason = "shared-secret-mismatch" },
+                    linked.Token).ConfigureAwait(false);
+                _logger.Warning("Sidecar IPC Hello rejected: shared-secret-mismatch");
+                return;
+            }
+
+            if (hello.ProtocolMajor != Hello.CurrentMajor)
+            {
+                await writer.WriteAsync(MessageKind.HelloAck,
+                    new HelloAck { Accepted = false, RejectReason = $"major-version-mismatch-peer={hello.ProtocolMajor}-server={Hello.CurrentMajor}" },
+                    linked.Token).ConfigureAwait(false);
+                _logger.Warning("Sidecar IPC Hello rejected: major mismatch peer={Peer} server={Server}",
+                    hello.ProtocolMajor, Hello.CurrentMajor);
+                return;
+            }
+
+            await writer.WriteAsync(MessageKind.HelloAck,
+                new HelloAck { Accepted = true, HostName = Environment.MachineName },
+                linked.Token).ConfigureAwait(false);
+
+            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;
+        }
+    }
+
+    /// <summary>
+    ///     Runs the server continuously, handling one connection at a time. When a connection
+    ///     ends (clean or error), accepts the next.
+    /// </summary>
+    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, "Sidecar 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();
+    }
+}
+
+/// <summary>
+///     Strategy for handling each post-Hello frame the pipe server reads. Implementations
+///     deserialize the body per the <see cref="MessageKind"/>, dispatch to the historian, and
+///     write the corresponding reply through the supplied <see cref="FrameWriter"/>.
+/// </summary>
+public interface IFrameHandler
+{
+    Task HandleAsync(MessageKind kind, byte[] body, FrameWriter writer, CancellationToken ct);
+}

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Program.cs

@@ -0,0 +1,110 @@
+using System;
+using System.Security.Principal;
+using System.Threading;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware;
+
+/// <summary>
+///     Entry point for the Wonderware Historian sidecar. Reads pipe name, allowed-SID,
+///     shared secret, and historian connection config from environment (the supervisor
+///     passes them at spawn time per <c>driver-stability.md</c>). Hosts a named-pipe server
+///     dispatching the five sidecar contracts (PR 3.3) to the Wonderware Historian SDK.
+/// </summary>
+public static class Program
+{
+    public static int Main(string[] args)
+    {
+        Log.Logger = new LoggerConfiguration()
+            .MinimumLevel.Information()
+            .WriteTo.File(
+                @"%ProgramData%\OtOpcUa\historian-wonderware-.log".Replace("%ProgramData%", Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData)),
+                rollingInterval: RollingInterval.Day)
+            .CreateLogger();
+
+        try
+        {
+            var pipeName = Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_PIPE")
+                ?? throw new InvalidOperationException("OTOPCUA_HISTORIAN_PIPE not set — supervisor must pass the sidecar pipe name");
+            var allowedSidValue = Environment.GetEnvironmentVariable("OTOPCUA_ALLOWED_SID")
+                ?? throw new InvalidOperationException("OTOPCUA_ALLOWED_SID not set — supervisor must pass the server principal SID");
+            var sharedSecret = Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_SECRET")
+                ?? throw new InvalidOperationException("OTOPCUA_HISTORIAN_SECRET not set — supervisor must pass the per-process secret at spawn time");
+
+            var allowedSid = new SecurityIdentifier(allowedSidValue);
+
+            using var cts = new CancellationTokenSource();
+            Console.CancelKeyPress += (_, e) => { e.Cancel = true; cts.Cancel(); };
+
+            // Sidecar can boot in "pipe-only" mode (no real Wonderware Historian SDK
+            // initialization) for smoke + IPC tests. Production sets ENABLED=true so the
+            // SDK opens its connection up front.
+            var historianEnabled = string.Equals(
+                Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_ENABLED"),
+                "true", StringComparison.OrdinalIgnoreCase);
+
+            if (!historianEnabled)
+            {
+                Log.Information("Wonderware historian sidecar starting in pipe-only mode (OTOPCUA_HISTORIAN_ENABLED!=true) — pipe={Pipe} allowedSid={Sid}", pipeName, allowedSidValue);
+                cts.Token.WaitHandle.WaitOne();
+                Log.Information("Wonderware historian sidecar stopping cleanly");
+                return 0;
+            }
+
+            using var historian = BuildHistorian();
+            var handler = new HistorianFrameHandler(historian, Log.Logger);
+            using var server = new PipeServer(pipeName, allowedSid, sharedSecret, Log.Logger);
+
+            Log.Information("Wonderware historian sidecar serving — pipe={Pipe} allowedSid={Sid}", pipeName, allowedSidValue);
+            try { server.RunAsync(handler, cts.Token).GetAwaiter().GetResult(); }
+            catch (OperationCanceledException) { /* clean shutdown via Ctrl-C */ }
+
+            Log.Information("Wonderware historian sidecar stopped cleanly");
+            return 0;
+        }
+        catch (Exception ex)
+        {
+            Log.Fatal(ex, "Wonderware historian sidecar fatal");
+            return 2;
+        }
+        finally { Log.CloseAndFlush(); }
+    }
+
+    /// <summary>
+    ///     Builds the Wonderware Historian data source from environment variables. Mirrors
+    ///     the env-var contract that <c>Driver.Galaxy.Host</c> used in v1; PR 3.W reaffirms
+    ///     this contract in install scripts.
+    /// </summary>
+    private static HistorianDataSource BuildHistorian()
+    {
+        var cfg = new HistorianConfiguration
+        {
+            Enabled = true,
+            ServerName = Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_SERVER") ?? "localhost",
+            Port = TryParseInt("OTOPCUA_HISTORIAN_PORT", 32568),
+            IntegratedSecurity = !string.Equals(Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_INTEGRATED"), "false", StringComparison.OrdinalIgnoreCase),
+            UserName = Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_USER"),
+            Password = Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_PASS"),
+            CommandTimeoutSeconds = TryParseInt("OTOPCUA_HISTORIAN_TIMEOUT_SEC", 30),
+            MaxValuesPerRead = TryParseInt("OTOPCUA_HISTORIAN_MAX_VALUES", 10000),
+            FailureCooldownSeconds = TryParseInt("OTOPCUA_HISTORIAN_COOLDOWN_SEC", 60),
+        };
+
+        var servers = Environment.GetEnvironmentVariable("OTOPCUA_HISTORIAN_SERVERS");
+        if (!string.IsNullOrWhiteSpace(servers))
+            cfg.ServerNames = new System.Collections.Generic.List<string>(
+                servers.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries));
+
+        Log.Information("Sidecar Historian config — {NodeCount} node(s), port={Port}",
+            cfg.ServerNames.Count > 0 ? cfg.ServerNames.Count : 1, cfg.Port);
+        return new HistorianDataSource(cfg);
+    }
+
+    private static int TryParseInt(string envName, int defaultValue)
+    {
+        var raw = Environment.GetEnvironmentVariable(envName);
+        return int.TryParse(raw, out var parsed) ? parsed : defaultValue;
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.csproj

@@ -0,0 +1,68 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net48</TargetFramework>
+        <!-- x86 to match the in-process bitness expectations of the Wonderware Historian SDK
+             that PR 3.2 lifted in. Mirrors Driver.Galaxy.Host's bitness for consistency. -->
+        <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.Historian.Wonderware</RootNamespace>
+        <AssemblyName>OtOpcUa.Driver.Historian.Wonderware</AssemblyName>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="MessagePack" Version="2.5.187"/>
+        <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="System.Data.SqlClient" Version="4.9.0"/>
+        <PackageReference Include="Serilog" Version="4.2.0"/>
+        <PackageReference Include="Serilog.Sinks.File" Version="7.0.0"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <!-- Wonderware Historian SDK — consumed by Backend/ for HistoryReadAsync.
+             Lifted from Driver.Galaxy.Host in PR 3.2 so the sidecar owns the SDK. -->
+        <Reference Include="aahClientManaged">
+            <HintPath>..\..\lib\aahClientManaged.dll</HintPath>
+            <EmbedInteropTypes>false</EmbedInteropTypes>
+        </Reference>
+        <Reference Include="aahClientCommon">
+            <HintPath>..\..\lib\aahClientCommon.dll</HintPath>
+            <EmbedInteropTypes>false</EmbedInteropTypes>
+        </Reference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <!-- Historian SDK native and satellite DLLs — staged beside the host exe so the
+             aahClientManaged wrapper can P/Invoke into them without an AssemblyResolve hook. -->
+        <None Include="..\..\lib\aahClient.dll">
+            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+        </None>
+        <None Include="..\..\lib\Historian.CBE.dll">
+            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+        </None>
+        <None Include="..\..\lib\Historian.DPAPI.dll">
+            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+        </None>
+        <None Include="..\..\lib\ArchestrA.CloudHistorian.Contract.dll">
+            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+        </None>
+    </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.Modbus/ModbusAutoProhibition.cs

@@ -0,0 +1,23 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+/// <summary>
+///     #152 — operator-visible snapshot of one auto-prohibited coalesced range. Returned in
+///     bulk by <see cref="ModbusDriver.GetAutoProhibitedRanges"/>; consumers (Admin UI,
+///     dashboards, log-aggregation pipelines) project the list into whatever shape they need.
+/// </summary>
+/// <param name="UnitId">Modbus unit ID (slave) the prohibition applies to.</param>
+/// <param name="Region">Register region (HoldingRegisters / InputRegisters / Coils / DiscreteInputs).</param>
+/// <param name="StartAddress">Inclusive start of the prohibited range (zero-based PDU offset).</param>
+/// <param name="EndAddress">Inclusive end of the prohibited range. Equals <paramref name="StartAddress"/> when bisection has narrowed to a single register.</param>
+/// <param name="LastProbedUtc">Wall-clock time of the most recent failure (record) or re-probe (refresh).</param>
+/// <param name="BisectionPending">
+///     True when the range still spans &gt; 1 register and the next re-probe will bisect it
+///     (per #150). False when the range is single-register or has been pinned permanent.
+/// </param>
+public sealed record ModbusAutoProhibition(
+    byte UnitId,
+    ModbusRegion Region,
+    ushort StartAddress,
+    ushort EndAddress,
+    DateTime LastProbedUtc,
+    bool BisectionPending);

src/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusDriver.cs

@@ -1,5 +1,7 @@
 using System.Buffers.Binary;
 using System.Text.Json;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
@@ -57,12 +59,16 @@ public sealed class ModbusDriver
     private DriverHealth _health = new(DriverState.Unknown, null, null);
     private readonly Dictionary<string, ModbusTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
 
+    private readonly ILogger<ModbusDriver> _logger;
+
     public ModbusDriver(ModbusDriverOptions options, string driverInstanceId,
-        Func<ModbusDriverOptions, IModbusTransport>? transportFactory = null)
+        Func<ModbusDriverOptions, IModbusTransport>? transportFactory = null,
+        ILogger<ModbusDriver>? logger = null)
     {
         ArgumentNullException.ThrowIfNull(options);
         _options = options;
         _driverInstanceId = driverInstanceId;
+        _logger = logger ?? NullLogger<ModbusDriver>.Instance;
         _transportFactory = transportFactory
             ?? (o => new ModbusTcpTransport(
                 o.Host, o.Port, o.Timeout, o.AutoReconnect,
@@ -409,7 +415,19 @@ public sealed class ModbusDriver
     ///     Cleared by ReinitializeAsync (operator restart) or by an explicit re-probe API
     ///     (not yet shipped).
     /// </summary>
-    private readonly Dictionary<(byte Unit, ModbusRegion Region, ushort Start, ushort End), DateTime> _autoProhibited = new();
+    /// <summary>
+    ///     #150 — per-prohibition state. <c>SplitPending</c> drives the re-probe loop's
+    ///     bisection: when true and the range spans &gt; 1 register, the next re-probe
+    ///     tries the two halves separately to narrow the actual offending register(s).
+    ///     Single-register prohibitions can't be split further; they stay re-probed as-is.
+    /// </summary>
+    private sealed class ProhibitionState
+    {
+        public DateTime LastProbedUtc;
+        public bool SplitPending;
+    }
+
+    private readonly Dictionary<(byte Unit, ModbusRegion Region, ushort Start, ushort End), ProhibitionState> _autoProhibited = new();
     private readonly object _autoProhibitedLock = new();
     private CancellationTokenSource? _reprobeCts;
 
@@ -431,7 +449,53 @@ public sealed class ModbusDriver
 
     private void RecordAutoProhibition(byte unit, ModbusRegion region, ushort start, ushort end)
     {
-        lock (_autoProhibitedLock) _autoProhibited[(unit, region, start, end)] = DateTime.UtcNow;
+        bool isNew;
+        lock (_autoProhibitedLock)
+        {
+            // Multi-register prohibitions enter the bisection workflow on the next re-probe;
+            // single-register prohibitions are already minimal and skip bisection.
+            isNew = !_autoProhibited.ContainsKey((unit, region, start, end));
+            _autoProhibited[(unit, region, start, end)] = new ProhibitionState
+            {
+                LastProbedUtc = DateTime.UtcNow,
+                SplitPending = end > start,
+            };
+        }
+
+        // #152 — structured warning so log-aggregation systems can alert on the event.
+        // First-time prohibitions get logged; re-fires of the same range stay quiet to avoid
+        // flooding when a per-tick exception keeps the same range bad. The state visible via
+        // GetAutoProhibitedRanges shows operators the long-tail picture.
+        if (isNew)
+            _logger.LogWarning(
+                "Modbus coalesced read failed; auto-prohibited range recorded. Driver={DriverInstanceId} Unit={Unit} Region={Region} Start={Start} End={End} Span={Span}",
+                _driverInstanceId, unit, region, start, end, end - start + 1);
+    }
+
+    /// <summary>
+    ///     #153 — info log when a re-probe clears a prohibition. Operators see recovery
+    ///     events without having to poll <see cref="GetAutoProhibitedRanges"/>.
+    /// </summary>
+    private void LogProhibitionCleared(byte unit, ModbusRegion region, ushort start, ushort end) =>
+        _logger.LogInformation(
+            "Modbus auto-prohibition cleared by re-probe. Driver={DriverInstanceId} Unit={Unit} Region={Region} Start={Start} End={End}",
+            _driverInstanceId, unit, region, start, end);
+
+    /// <summary>
+    ///     #152 — operator-visible snapshot of every range the planner has learned to read
+    ///     individually. Exposed through the driver-diagnostics surface; consumers (Admin UI,
+    ///     log-aggregation, dashboards) call this to show what's been auto-isolated. Populated
+    ///     on coalesced-read failure (#148), narrowed by bisection (#150), cleared by the
+    ///     re-probe loop (#151) when ranges become healthy again.
+    /// </summary>
+    public IReadOnlyList<ModbusAutoProhibition> GetAutoProhibitedRanges()
+    {
+        lock (_autoProhibitedLock)
+            return _autoProhibited
+                .Select(kv => new ModbusAutoProhibition(
+                    kv.Key.Unit, kv.Key.Region, kv.Key.Start, kv.Key.End,
+                    kv.Value.LastProbedUtc, kv.Value.SplitPending))
+                .ToArray();
     }
 
     /// <summary>Test/diagnostic accessor — returns the current auto-prohibited range count.</summary>
@@ -441,78 +505,132 @@ public sealed class ModbusDriver
     }
 
     /// <summary>
-    ///     #151 — periodic re-probe loop. Wakes every <c>AutoProhibitReprobeInterval</c> and
-    ///     retries each auto-prohibited range with a one-shot coalesced read. Successful
-    ///     re-probes drop the prohibition; failed ones leave it in place + bump the
-    ///     last-probed timestamp so the next attempt waits another full interval.
-    ///     Lives for the driver lifetime; cancelled by <c>ShutdownAsync</c>.
+    ///     #151 — periodic re-probe loop, augmented in #150 with bisection-style narrowing.
+    ///     Each tick processes every prohibition: split-pending multi-register ranges get
+    ///     bisected (try left + right halves; replace with whichever halves still fail),
+    ///     single-register or non-split-pending ranges get a straight re-probe. Lives for
+    ///     the driver lifetime; cancelled by <c>ShutdownAsync</c>.
     /// </summary>
     private async Task ReprobeLoopAsync(CancellationToken ct)
     {
         var interval = _options.AutoProhibitReprobeInterval!.Value;
-        var transport = _transport;
         while (!ct.IsCancellationRequested)
         {
             try { await Task.Delay(interval, ct).ConfigureAwait(false); }
             catch (OperationCanceledException) { return; }
-
-            if (transport is null) continue;
-
-            // Snapshot the prohibition set so we can release the lock during the wire calls.
-            (byte Unit, ModbusRegion Region, ushort Start, ushort End)[] candidates;
-            lock (_autoProhibitedLock)
-                candidates = _autoProhibited.Keys.ToArray();
-
-            foreach (var p in candidates)
-            {
-                if (ct.IsCancellationRequested) return;
-                var fc = p.Region == ModbusRegion.HoldingRegisters ? (byte)0x03 : (byte)0x04;
-                var qty = (ushort)(p.End - p.Start + 1);
-                try
-                {
-                    using var probeCts = CancellationTokenSource.CreateLinkedTokenSource(ct);
-                    probeCts.CancelAfter(_options.Timeout);
-                    _ = await ReadRegisterBlockAsync(transport, p.Unit, fc, p.Start, qty, probeCts.Token).ConfigureAwait(false);
-                    // Range is healthy now — drop the prohibition. Next data scan re-coalesces normally.
-                    lock (_autoProhibitedLock) _autoProhibited.Remove(p);
-                }
+            try { await RunReprobeOnceForTestAsync(ct).ConfigureAwait(false); }
             catch (OperationCanceledException) when (ct.IsCancellationRequested) { return; }
-                catch
-                {
-                    // Still bad. Bump the timestamp so it shows up on diagnostics as recently
-                    // re-probed — the prohibition stays in place.
-                    lock (_autoProhibitedLock)
-                    {
-                        if (_autoProhibited.ContainsKey(p))
-                            _autoProhibited[p] = DateTime.UtcNow;
-                    }
-                }
-            }
         }
     }
 
-    /// <summary>Test/diagnostic accessor — fires one re-probe pass synchronously for tests.</summary>
+    /// <summary>
+    ///     One re-probe pass. Public-but-internal so tests can drive it synchronously rather
+    ///     than wait on the background timer. Iterates a snapshot of the prohibition set; for
+    ///     each entry decides between bisection (multi-register + SplitPending) or straight
+    ///     retry (single-register or already-narrowed).
+    /// </summary>
     internal async Task RunReprobeOnceForTestAsync(CancellationToken ct)
     {
         var transport = _transport ?? throw new InvalidOperationException("Transport not connected");
-        (byte Unit, ModbusRegion Region, ushort Start, ushort End)[] candidates;
-        lock (_autoProhibitedLock) candidates = _autoProhibited.Keys.ToArray();
-        foreach (var p in candidates)
+
+        ((byte Unit, ModbusRegion Region, ushort Start, ushort End) Key, bool SplitPending)[] candidates;
+        lock (_autoProhibitedLock)
+            candidates = _autoProhibited
+                .Select(kv => (Key: kv.Key, SplitPending: kv.Value.SplitPending))
+                .ToArray();
+
+        foreach (var (key, splitPending) in candidates)
         {
-            var fc = p.Region == ModbusRegion.HoldingRegisters ? (byte)0x03 : (byte)0x04;
-            var qty = (ushort)(p.End - p.Start + 1);
+            if (ct.IsCancellationRequested) return;
+            if (splitPending && key.End > key.Start)
+                await BisectAndReprobeAsync(transport, key, ct).ConfigureAwait(false);
+            else
+                await StraightReprobeAsync(transport, key, ct).ConfigureAwait(false);
+        }
+    }
+
+    private async Task StraightReprobeAsync(IModbusTransport transport,
+        (byte Unit, ModbusRegion Region, ushort Start, ushort End) key, CancellationToken ct)
+    {
+        var fc = key.Region == ModbusRegion.HoldingRegisters ? (byte)0x03 : (byte)0x04;
+        var qty = (ushort)(key.End - key.Start + 1);
         try
         {
-                _ = await ReadRegisterBlockAsync(transport, p.Unit, fc, p.Start, qty, ct).ConfigureAwait(false);
-                lock (_autoProhibitedLock) _autoProhibited.Remove(p);
+            _ = await ReadRegisterBlockAsync(transport, key.Unit, fc, key.Start, qty, ct).ConfigureAwait(false);
+            lock (_autoProhibitedLock) _autoProhibited.Remove(key);
+            LogProhibitionCleared(key.Unit, key.Region, key.Start, key.End);
         }
+        catch (OperationCanceledException) when (ct.IsCancellationRequested) { throw; }
         catch
         {
             lock (_autoProhibitedLock)
-                    if (_autoProhibited.ContainsKey(p))
-                        _autoProhibited[p] = DateTime.UtcNow;
+                if (_autoProhibited.TryGetValue(key, out var st)) st.LastProbedUtc = DateTime.UtcNow;
         }
     }
+
+    /// <summary>
+    ///     #150 — bisect a multi-register prohibition. Removes the parent entry and re-adds
+    ///     whichever halves still fail. Over multiple re-probe ticks the prohibition narrows
+    ///     log2(span) times until it pinpoints the actual protected register(s).
+    /// </summary>
+    private async Task BisectAndReprobeAsync(IModbusTransport transport,
+        (byte Unit, ModbusRegion Region, ushort Start, ushort End) key, CancellationToken ct)
+    {
+        var fc = key.Region == ModbusRegion.HoldingRegisters ? (byte)0x03 : (byte)0x04;
+        var mid = (ushort)((key.Start + key.End) / 2);
+        var leftEnd = mid;
+        var rightStart = (ushort)(mid + 1);
+
+        var leftFailed = await ProbeFailsAsync(transport, fc, key.Unit, key.Start, leftEnd, ct).ConfigureAwait(false);
+        var rightFailed = await ProbeFailsAsync(transport, fc, key.Unit, rightStart, key.End, ct).ConfigureAwait(false);
+
+        lock (_autoProhibitedLock)
+        {
+            _autoProhibited.Remove(key);
+            if (leftFailed)
+            {
+                _autoProhibited[(key.Unit, key.Region, key.Start, leftEnd)] = new ProhibitionState
+                {
+                    LastProbedUtc = DateTime.UtcNow,
+                    SplitPending = leftEnd > key.Start,
+                };
+            }
+            if (rightFailed)
+            {
+                _autoProhibited[(key.Unit, key.Region, rightStart, key.End)] = new ProhibitionState
+                {
+                    LastProbedUtc = DateTime.UtcNow,
+                    SplitPending = key.End > rightStart,
+                };
+            }
+            // Both halves succeeded → entry is just removed. The parent prohibition is gone
+            // and the next normal scan can re-coalesce across the whole original range.
+        }
+
+        // #153 — log per-half outcome OUTSIDE the lock (logger calls can be expensive).
+        // Both halves clear → emit a single combined "fully cleared" line.
+        if (!leftFailed && !rightFailed)
+            LogProhibitionCleared(key.Unit, key.Region, key.Start, key.End);
+        else
+        {
+            if (!leftFailed)
+                LogProhibitionCleared(key.Unit, key.Region, key.Start, leftEnd);
+            if (!rightFailed)
+                LogProhibitionCleared(key.Unit, key.Region, rightStart, key.End);
+        }
+    }
+
+    private async Task<bool> ProbeFailsAsync(IModbusTransport transport, byte fc, byte unit,
+        ushort start, ushort end, CancellationToken ct)
+    {
+        var qty = (ushort)(end - start + 1);
+        try
+        {
+            _ = await ReadRegisterBlockAsync(transport, unit, fc, start, qty, ct).ConfigureAwait(false);
+            return false;
+        }
+        catch (OperationCanceledException) when (ct.IsCancellationRequested) { throw; }
+        catch { return true; }
     }
 
     /// <summary>

src/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusDriverFactoryExtensions.cs

@@ -1,5 +1,6 @@
 using System.Text.Json;
 using System.Text.Json.Serialization;
+using Microsoft.Extensions.Logging;
 using ZB.MOM.WW.OtOpcUa.Core.Hosting;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
@@ -14,13 +15,25 @@ public static class ModbusDriverFactoryExtensions
 {
     public const string DriverTypeName = "Modbus";
 
-    public static void Register(DriverFactoryRegistry registry)
+    /// <summary>
+    ///     Register the Modbus factory with the driver registry. The optional
+    ///     <paramref name="loggerFactory"/> is captured at registration time and used to
+    ///     construct an <see cref="ILogger{ModbusDriver}"/> per driver instance — without it,
+    ///     the driver runs with the null logger (existing tests and standalone callers stay
+    ///     unchanged).
+    /// </summary>
+    public static void Register(DriverFactoryRegistry registry, ILoggerFactory? loggerFactory = null)
     {
         ArgumentNullException.ThrowIfNull(registry);
-        registry.Register(DriverTypeName, CreateInstance);
+        registry.Register(DriverTypeName, (id, json) => CreateInstance(id, json, loggerFactory));
     }
 
-    internal static ModbusDriver CreateInstance(string driverInstanceId, string driverConfigJson)
+    /// <summary>Public for the Server-side bootstrapper + test consumers (Admin.Tests, etc.).</summary>
+    public static ModbusDriver CreateInstance(string driverInstanceId, string driverConfigJson)
+        => CreateInstance(driverInstanceId, driverConfigJson, loggerFactory: null);
+
+    /// <summary>Logger-aware overload — used by <see cref="Register"/>'s closure when wired through DI.</summary>
+    public static ModbusDriver CreateInstance(string driverInstanceId, string driverConfigJson, ILoggerFactory? loggerFactory)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(driverInstanceId);
         ArgumentException.ThrowIfNullOrWhiteSpace(driverConfigJson);
@@ -46,6 +59,7 @@ public static class ModbusDriverFactoryExtensions
             UseFC16ForSingleRegisterWrites = dto.UseFC16ForSingleRegisterWrites ?? false,
             DisableFC23 = dto.DisableFC23 ?? false,
             WriteOnChangeOnly = dto.WriteOnChangeOnly ?? false,
+            MaxReadGap = dto.MaxReadGap ?? 0,
             Family = dto.Family is null ? ModbusFamily.Generic
                 : ParseEnum<ModbusFamily>(dto.Family, "<driver-level>", driverInstanceId, "Family"),
             MelsecSubFamily = dto.MelsecSubFamily is null ? MelsecFamily.Q_L_iQR
@@ -83,7 +97,10 @@ public static class ModbusDriverFactoryExtensions
             },
         };
 
-        return new ModbusDriver(options, driverInstanceId);
+        return new ModbusDriver(
+            options, driverInstanceId,
+            transportFactory: null,
+            logger: loggerFactory?.CreateLogger<ModbusDriver>());
     }
 
     private static ModbusTagDefinition BuildTag(ModbusTagDto t, string driverInstanceId)
@@ -174,6 +191,7 @@ public static class ModbusDriverFactoryExtensions
         public bool? UseFC16ForSingleRegisterWrites { get; init; }
         public bool? DisableFC23 { get; init; }
         public bool? WriteOnChangeOnly { get; init; }
+        public ushort? MaxReadGap { get; init; }
         public string? Family { get; init; }
         public string? MelsecSubFamily { get; init; }
         public int? AutoProhibitReprobeMs { get; init; }

src/ZB.MOM.WW.OtOpcUa.Server/Alarms/AlarmConditionService.cs

@@ -0,0 +1,289 @@
+using System.Collections.Concurrent;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Alarms;
+
+/// <summary>
+///     Server-level alarm-condition state machine. Tracks one entry per registered
+///     condition; consumes value changes from the four sub-attribute references in
+///     <see cref="AlarmConditionInfo"/> (InAlarm / Priority / Description / Acked) and
+///     raises <see cref="TransitionRaised"/> on Active / Acknowledged / Inactive
+///     transitions per OPC UA Part 9 (simplified). Operator acknowledgement routes
+///     through <see cref="IAlarmAcknowledger"/> against <c>AckMsgWriteRef</c>.
+/// </summary>
+/// <remarks>
+///     This is the driver-agnostic replacement for <c>GalaxyAlarmTracker</c>. The
+///     service does not own subscription lifecycle — PR 2.3 will wire DriverNodeManager
+///     to subscribe through the driver's <c>ISubscribable</c> and forward value changes
+///     here via <see cref="OnValueChanged"/>. Keeping the service free of subscription
+///     plumbing makes it trivially testable and lets future drivers feed it from any
+///     value source (in-process, gRPC, named pipe).
+/// </remarks>
+public sealed class AlarmConditionService : IDisposable
+{
+    private readonly Func<DateTime> _clock;
+
+    // ConditionId → state.
+    private readonly ConcurrentDictionary<string, AlarmConditionState> _conditions =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    // Sub-attribute full ref → (conditionId, which field). Multiple conditions may
+    // observe the same sub-attribute (rare but legal); the value is a list to support
+    // fan-out on a single value change.
+    private readonly ConcurrentDictionary<string, List<(string ConditionId, AlarmField Field)>> _refToCondition =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    private readonly object _refMapLock = new();
+
+    private bool _disposed;
+
+    /// <summary>
+    ///     Fired when a registered condition transitions Active / Acknowledged / Inactive.
+    ///     Handlers must be cheap; the event is raised on whatever thread feeds
+    ///     <see cref="OnValueChanged"/> and blocks the value-change pipeline.
+    /// </summary>
+    public event EventHandler<AlarmConditionTransition>? TransitionRaised;
+
+    public AlarmConditionService() : this(() => DateTime.UtcNow) { }
+
+    /// <summary>Test seam — inject a fixed clock for deterministic transition timestamps.</summary>
+    internal AlarmConditionService(Func<DateTime> clock)
+    {
+        _clock = clock ?? throw new ArgumentNullException(nameof(clock));
+    }
+
+    /// <summary>Number of currently tracked conditions. Diagnostic only.</summary>
+    public int TrackedCount => _conditions.Count;
+
+    /// <summary>
+    ///     Register a condition. Idempotent — repeat calls for the same
+    ///     <paramref name="conditionId"/> are a no-op. The acker is captured for the
+    ///     condition's lifetime; pass null when the driver does not accept acks.
+    /// </summary>
+    public void Track(string conditionId, AlarmConditionInfo info, IAlarmAcknowledger? acker = null)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        ArgumentException.ThrowIfNullOrWhiteSpace(conditionId);
+        ArgumentNullException.ThrowIfNull(info);
+
+        var state = new AlarmConditionState(conditionId, info, acker);
+        if (!_conditions.TryAdd(conditionId, state)) return;
+
+        lock (_refMapLock)
+        {
+            AddRefMapping(info.InAlarmRef, conditionId, AlarmField.InAlarm);
+            AddRefMapping(info.PriorityRef, conditionId, AlarmField.Priority);
+            AddRefMapping(info.DescAttrNameRef, conditionId, AlarmField.DescAttrName);
+            AddRefMapping(info.AckedRef, conditionId, AlarmField.Acked);
+        }
+    }
+
+    /// <summary>Deregister a condition. No-op when not tracked.</summary>
+    public void Untrack(string conditionId)
+    {
+        if (_disposed) return;
+        if (!_conditions.TryRemove(conditionId, out var state)) return;
+
+        lock (_refMapLock)
+        {
+            RemoveRefMapping(state.Info.InAlarmRef, conditionId);
+            RemoveRefMapping(state.Info.PriorityRef, conditionId);
+            RemoveRefMapping(state.Info.DescAttrNameRef, conditionId);
+            RemoveRefMapping(state.Info.AckedRef, conditionId);
+        }
+    }
+
+    /// <summary>
+    ///     Returns the set of sub-attribute references the service currently needs
+    ///     subscribed. Callers wire one subscription per ref through the driver's
+    ///     <see cref="ISubscribable"/>; PR 2.3 owns that wiring.
+    /// </summary>
+    public IReadOnlyCollection<string> GetSubscribedReferences()
+    {
+        lock (_refMapLock) return [.. _refToCondition.Keys];
+    }
+
+    /// <summary>
+    ///     Operator acknowledgement entry point. Returns false when the condition is
+    ///     not tracked, the condition has no acker registered, the condition has no
+    ///     <c>AckMsgWriteRef</c>, or the acker reports the write failed.
+    /// </summary>
+    public Task<bool> AcknowledgeAsync(string conditionId, string comment, CancellationToken cancellationToken = default)
+    {
+        if (_disposed || !_conditions.TryGetValue(conditionId, out var state))
+            return Task.FromResult(false);
+        if (state.Acker is null || string.IsNullOrEmpty(state.Info.AckMsgWriteRef))
+            return Task.FromResult(false);
+        return state.Acker.WriteAckMessageAsync(state.Info.AckMsgWriteRef, comment ?? string.Empty, cancellationToken);
+    }
+
+    /// <summary>
+    ///     Snapshot every tracked condition's current state. Diagnostic / dashboard use only.
+    /// </summary>
+    public IReadOnlyList<AlarmConditionSnapshot> Snapshot()
+    {
+        return [.. _conditions.Values.Select(s =>
+        {
+            lock (s.Lock)
+                return new AlarmConditionSnapshot(s.ConditionId, s.InAlarm, s.Acked, s.Priority, s.Description);
+        })];
+    }
+
+    /// <summary>
+    ///     Feed a value change for one of the registered sub-attribute references.
+    ///     The service runs the state machine and raises <see cref="TransitionRaised"/>
+    ///     when the change produces a lifecycle transition. Unknown references are
+    ///     silently dropped — the caller may register and unregister concurrently with
+    ///     value-change delivery, and a stale callback for a recently-untracked
+    ///     condition must not throw.
+    /// </summary>
+    public void OnValueChanged(string fullReference, DataValueSnapshot value)
+    {
+        if (_disposed) return;
+        if (string.IsNullOrEmpty(fullReference)) return;
+
+        List<(string ConditionId, AlarmField Field)>? targets;
+        lock (_refMapLock)
+        {
+            if (!_refToCondition.TryGetValue(fullReference, out targets) || targets.Count == 0) return;
+            // Snapshot under lock; the state machine runs outside.
+            targets = [.. targets];
+        }
+
+        var now = _clock();
+        foreach (var (conditionId, field) in targets)
+        {
+            if (!_conditions.TryGetValue(conditionId, out var state)) continue;
+
+            AlarmConditionTransition? transition = null;
+            lock (state.Lock)
+            {
+                transition = ApplyValue(state, field, value, now);
+            }
+
+            if (transition is { } t)
+            {
+                TransitionRaised?.Invoke(this, t);
+            }
+        }
+    }
+
+    /// <summary>
+    ///     Apply one value change to one condition. Returns a transition when the
+    ///     change crosses a state boundary; null otherwise. Caller holds <c>state.Lock</c>.
+    /// </summary>
+    private static AlarmConditionTransition? ApplyValue(
+        AlarmConditionState state, AlarmField field, DataValueSnapshot value, DateTime now)
+    {
+        AlarmConditionTransition? transition = null;
+        state.LastUpdateUtc = now;
+
+        switch (field)
+        {
+            case AlarmField.InAlarm:
+            {
+                var wasActive = state.InAlarm;
+                var isActive = value.Value is bool b && b;
+                state.InAlarm = isActive;
+                if (!wasActive && isActive)
+                {
+                    // Reset Acked on every active transition so a re-alarm requires fresh ack.
+                    state.Acked = false;
+                    transition = new AlarmConditionTransition(
+                        state.ConditionId, AlarmStateTransition.Active,
+                        state.Priority, state.Description, now);
+                }
+                else if (wasActive && !isActive)
+                {
+                    transition = new AlarmConditionTransition(
+                        state.ConditionId, AlarmStateTransition.Inactive,
+                        state.Priority, state.Description, now);
+                }
+                break;
+            }
+            case AlarmField.Priority:
+                state.Priority = CoercePriority(value.Value, state.Priority);
+                break;
+            case AlarmField.DescAttrName:
+                state.Description = value.Value as string;
+                break;
+            case AlarmField.Acked:
+            {
+                var wasAcked = state.Acked;
+                var isAcked = value.Value is bool b && b;
+                state.Acked = isAcked;
+                // Only fire Acknowledged on false → true while still active. The first
+                // post-Track callback often arrives with isAcked == wasAcked (state starts
+                // Acked=true so an initially-quiet alarm doesn't misfire).
+                if (!wasAcked && isAcked && state.InAlarm)
+                {
+                    transition = new AlarmConditionTransition(
+                        state.ConditionId, AlarmStateTransition.Acknowledged,
+                        state.Priority, state.Description, now);
+                }
+                break;
+            }
+        }
+
+        return transition;
+    }
+
+    private static int CoercePriority(object? raw, int fallback) => raw switch
+    {
+        int i => i,
+        short s => s,
+        long l when l <= int.MaxValue => (int)l,
+        byte b => b,
+        ushort us => us,
+        uint ui when ui <= int.MaxValue => (int)ui,
+        _ => fallback,
+    };
+
+    private void AddRefMapping(string? fullRef, string conditionId, AlarmField field)
+    {
+        if (string.IsNullOrEmpty(fullRef)) return;
+        if (!_refToCondition.TryGetValue(fullRef, out var list))
+        {
+            list = [];
+            _refToCondition[fullRef] = list;
+        }
+        list.Add((conditionId, field));
+    }
+
+    private void RemoveRefMapping(string? fullRef, string conditionId)
+    {
+        if (string.IsNullOrEmpty(fullRef)) return;
+        if (!_refToCondition.TryGetValue(fullRef, out var list)) return;
+        list.RemoveAll(t => string.Equals(t.ConditionId, conditionId, StringComparison.OrdinalIgnoreCase));
+        if (list.Count == 0) _refToCondition.TryRemove(fullRef, out _);
+    }
+
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        _conditions.Clear();
+        lock (_refMapLock) _refToCondition.Clear();
+    }
+
+    private enum AlarmField { InAlarm, Priority, DescAttrName, Acked }
+
+    /// <summary>Per-condition mutable state. Access guarded by <see cref="Lock"/>.</summary>
+    private sealed class AlarmConditionState(string conditionId, AlarmConditionInfo info, IAlarmAcknowledger? acker)
+    {
+        public readonly object Lock = new();
+        public string ConditionId { get; } = conditionId;
+        public AlarmConditionInfo Info { get; } = info;
+        public IAlarmAcknowledger? Acker { get; } = acker;
+
+        public bool InAlarm;
+
+        // Default Acked=true so the first post-Track callback (.Acked=true on a quiet
+        // alarm) doesn't misfire as a transition. Active sets it back to false.
+        public bool Acked = true;
+
+        public int Priority;
+        public string? Description;
+        public DateTime LastUpdateUtc;
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Server/Alarms/AlarmConditionTransition.cs

@@ -0,0 +1,44 @@
+namespace ZB.MOM.WW.OtOpcUa.Server.Alarms;
+
+/// <summary>
+///     Lifecycle transition for an alarm condition. Mirrors OPC UA Part 9 alarm states
+///     simplified to the active / acknowledged / inactive triplet that every driver in
+///     the repo exposes today.
+/// </summary>
+public enum AlarmStateTransition
+{
+    /// <summary>InAlarm flipped false → true. Default to unacknowledged.</summary>
+    Active,
+
+    /// <summary>Acked flipped false → true while the alarm is still active.</summary>
+    Acknowledged,
+
+    /// <summary>InAlarm flipped true → false.</summary>
+    Inactive,
+}
+
+/// <summary>
+///     One alarm-state transition raised by <see cref="AlarmConditionService.TransitionRaised"/>.
+/// </summary>
+/// <param name="ConditionId">Stable identifier the caller registered the condition under (typically the driver's alarm full reference).</param>
+/// <param name="Transition">Which state the alarm transitioned to.</param>
+/// <param name="Priority">Latest known priority. 0 when no priority sub-attribute was registered or no value has been observed yet.</param>
+/// <param name="Description">Latest known description text; null when not registered or not yet observed.</param>
+/// <param name="AtUtc">Server-clock UTC of the value change that produced this transition.</param>
+public sealed record AlarmConditionTransition(
+    string ConditionId,
+    AlarmStateTransition Transition,
+    int Priority,
+    string? Description,
+    DateTime AtUtc);
+
+/// <summary>
+///     Read-only snapshot of an alarm condition's current state. Used for diagnostics
+///     and dashboards; not part of the live transition stream.
+/// </summary>
+public sealed record AlarmConditionSnapshot(
+    string ConditionId,
+    bool InAlarm,
+    bool Acked,
+    int Priority,
+    string? Description);

src/ZB.MOM.WW.OtOpcUa.Server/Alarms/IAlarmAcknowledger.cs

@@ -0,0 +1,23 @@
+namespace ZB.MOM.WW.OtOpcUa.Server.Alarms;
+
+/// <summary>
+///     Strategy for routing operator acknowledgement writes back to the underlying driver.
+///     Decouples <see cref="AlarmConditionService"/> from any specific driver's write API
+///     so the service can be tested without a real driver and reused across drivers with
+///     different write paths.
+/// </summary>
+/// <remarks>
+///     PR 2.3 supplies a default implementation that writes through the driver's
+///     <c>IWritable.WriteAsync</c> using the <c>AckMsgWriteRef</c> from
+///     <c>AlarmConditionInfo</c>. Drivers that route acks differently (e.g. a dedicated
+///     RPC) can supply a custom implementation when registering the condition.
+/// </remarks>
+public interface IAlarmAcknowledger
+{
+    /// <summary>
+    ///     Writes the operator's <paramref name="comment"/> to <paramref name="ackMsgWriteRef"/>.
+    ///     Returns true on driver-reported success, false otherwise. Implementations should
+    ///     propagate cancellation but never throw on a write that the driver cleanly rejects.
+    /// </summary>
+    Task<bool> WriteAckMessageAsync(string ackMsgWriteRef, string comment, CancellationToken cancellationToken);
+}

src/ZB.MOM.WW.OtOpcUa.Server/History/HistoryRouter.cs

@@ -0,0 +1,71 @@
+using System.Collections.Concurrent;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.History;
+
+/// <summary>
+///     Default <see cref="IHistoryRouter"/> implementation.
+/// </summary>
+public sealed class HistoryRouter : IHistoryRouter
+{
+    private readonly ConcurrentDictionary<string, IHistorianDataSource> _registry =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    private bool _disposed;
+
+    /// <inheritdoc />
+    public void Register(string fullReferencePrefix, IHistorianDataSource source)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        ArgumentNullException.ThrowIfNull(fullReferencePrefix);
+        ArgumentNullException.ThrowIfNull(source);
+
+        if (!_registry.TryAdd(fullReferencePrefix, source))
+        {
+            throw new InvalidOperationException(
+                $"A historian data source is already registered for prefix '{fullReferencePrefix}'.");
+        }
+    }
+
+    /// <inheritdoc />
+    public IHistorianDataSource? Resolve(string fullReference)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        ArgumentNullException.ThrowIfNull(fullReference);
+
+        // Longest-prefix match. Sources are typically a handful per server, so a linear
+        // scan is fine and avoids building a trie for a low-cardinality registry.
+        IHistorianDataSource? best = null;
+        var bestPrefixLength = -1;
+
+        foreach (var (prefix, source) in _registry)
+        {
+            if (fullReference.StartsWith(prefix, StringComparison.OrdinalIgnoreCase)
+                && prefix.Length > bestPrefixLength)
+            {
+                best = source;
+                bestPrefixLength = prefix.Length;
+            }
+        }
+
+        return best;
+    }
+
+    /// <summary>
+    ///     Disposes every registered source and prevents further registrations or
+    ///     resolutions. Sources may not all be disposable — null-safe disposal pattern.
+    /// </summary>
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+
+        foreach (var source in _registry.Values)
+        {
+            try { source.Dispose(); }
+            catch { /* best-effort — server shutdown should not throw on a misbehaving source */ }
+        }
+
+        _registry.Clear();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Server/History/IHistoryRouter.cs

@@ -0,0 +1,37 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.History;
+
+/// <summary>
+///     Server-level routing of OPC UA HistoryRead service calls to a registered
+///     <see cref="IHistorianDataSource"/>. One router per server instance; sources are
+///     registered at startup keyed by a driver-side full-reference prefix (typically the
+///     driver instance id).
+/// </summary>
+/// <remarks>
+///     <para>
+///         The router decouples history availability from the driver lifecycle: a driver
+///         can restart (or be temporarily disconnected) without taking history offline,
+///         and a single historian can serve nodes from multiple drivers.
+///     </para>
+///     <para>
+///         Resolution is by longest-prefix match so a per-driver source registered under
+///         <c>"galaxy"</c> wins over a fallback registered under empty string.
+///     </para>
+/// </remarks>
+public interface IHistoryRouter : IDisposable
+{
+    /// <summary>
+    ///     Resolves a full reference to its registered data source, or null when no source
+    ///     covers it.
+    /// </summary>
+    IHistorianDataSource? Resolve(string fullReference);
+
+    /// <summary>
+    ///     Registers a data source for full references that start with
+    ///     <paramref name="fullReferencePrefix"/>. Throws when the prefix is already
+    ///     registered — duplicate registrations indicate a startup-config bug rather than
+    ///     a runtime concern.
+    /// </summary>
+    void Register(string fullReferencePrefix, IHistorianDataSource source);
+}

src/ZB.MOM.WW.OtOpcUa.Server/Observability/HealthEndpointsHost.cs

@@ -5,6 +5,7 @@ using Microsoft.Extensions.Logging;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Core.Hosting;
 using ZB.MOM.WW.OtOpcUa.Core.Observability;
+using ZB.MOM.WW.OtOpcUa.Driver.Modbus;
 
 namespace ZB.MOM.WW.OtOpcUa.Server.Observability;
 
@@ -85,6 +86,13 @@ public sealed class HealthEndpointsHost : IAsyncDisposable
                     await WriteReadyzAsync(ctx).ConfigureAwait(false);
                     break;
                 default:
+                    // #154 — driver-diagnostics path family. URL shape:
+                    //   /diagnostics/drivers/{driverInstanceId}/modbus/auto-prohibited
+                    // Driver-agnostic at the URL level so future driver types (S7, AbCip,
+                    // FOCAS) can add their own per-type subpaths.
+                    if (path.StartsWith("/diagnostics/drivers/", StringComparison.Ordinal))
+                        await WriteDriverDiagnosticsAsync(ctx, path).ConfigureAwait(false);
+                    else
                         ctx.Response.StatusCode = 404;
                     break;
             }
@@ -157,6 +165,64 @@ public sealed class HealthEndpointsHost : IAsyncDisposable
         return list;
     }
 
+    /// <summary>
+    ///     #154 — driver-diagnostics endpoint family. Routes
+    ///     <c>/diagnostics/drivers/{driverId}/modbus/auto-prohibited</c> to the live
+    ///     <see cref="ModbusDriver"/> instance's <see cref="ModbusDriver.GetAutoProhibitedRanges"/>.
+    ///     404 when the driver instance doesn't exist; 400 when it exists but isn't a Modbus
+    ///     driver (the per-type endpoint is wrong for this row).
+    /// </summary>
+    private async Task WriteDriverDiagnosticsAsync(HttpListenerContext ctx, string path)
+    {
+        // Path shape: /diagnostics/drivers/{id}/modbus/auto-prohibited
+        var segments = path.Split('/', StringSplitOptions.RemoveEmptyEntries);
+        if (segments.Length < 4 || segments[0] != "diagnostics" || segments[1] != "drivers")
+        {
+            ctx.Response.StatusCode = 404;
+            return;
+        }
+
+        var driverId = segments[2];
+        var driver = _driverHost.GetDriver(driverId);
+        if (driver is null)
+        {
+            ctx.Response.StatusCode = 404;
+            await WriteBodyAsync(ctx, JsonSerializer.Serialize(new { error = $"Driver '{driverId}' not found" })).ConfigureAwait(false);
+            return;
+        }
+
+        // Per-driver-type subpath dispatch. Today only Modbus is wired; future drivers add
+        // their own segments[3] cases.
+        if (segments.Length >= 5 && segments[3] == "modbus" && segments[4] == "auto-prohibited")
+        {
+            if (driver is not ModbusDriver modbus)
+            {
+                ctx.Response.StatusCode = 400;
+                await WriteBodyAsync(ctx, JsonSerializer.Serialize(new { error = $"Driver '{driverId}' is not a Modbus driver (type: {driver.DriverType})" })).ConfigureAwait(false);
+                return;
+            }
+            var ranges = modbus.GetAutoProhibitedRanges();
+            ctx.Response.StatusCode = 200;
+            await WriteBodyAsync(ctx, JsonSerializer.Serialize(new
+            {
+                driverInstanceId = driverId,
+                count = ranges.Count,
+                ranges = ranges.Select(r => new
+                {
+                    unitId = r.UnitId,
+                    region = r.Region.ToString(),
+                    startAddress = r.StartAddress,
+                    endAddress = r.EndAddress,
+                    lastProbedUtc = r.LastProbedUtc,
+                    bisectionPending = r.BisectionPending,
+                }).ToArray(),
+            })).ConfigureAwait(false);
+            return;
+        }
+
+        ctx.Response.StatusCode = 404;
+    }
+
     private static async Task WriteBodyAsync(HttpListenerContext ctx, string body)
     {
         var bytes = Encoding.UTF8.GetBytes(body);

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

@@ -5,6 +5,8 @@ using Opc.Ua.Server;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Core.Authorization;
 using ZB.MOM.WW.OtOpcUa.Core.Resilience;
+using ZB.MOM.WW.OtOpcUa.Server.Alarms;
+using ZB.MOM.WW.OtOpcUa.Server.History;
 using ZB.MOM.WW.OtOpcUa.Server.Security;
 using DriverWriteRequest = ZB.MOM.WW.OtOpcUa.Core.Abstractions.WriteRequest;
 // Core.Abstractions defines a type-named HistoryReadResult (driver-side samples + continuation
@@ -85,10 +87,31 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
     private readonly IReadable? _virtualReadable;
     private readonly IReadable? _scriptedAlarmReadable;
 
+    // PR 1.3 — server-level history routing. When non-null + a source is registered for
+    // the requested full reference, the four HistoryRead* overrides dispatch through the
+    // router. Otherwise we fall back to the legacy `_driver as IHistoryProvider` path
+    // wrapped in a thin adapter, so existing tests and drivers that still implement
+    // IHistoryProvider directly keep working until PR 1.W flips DI to register the
+    // legacy path inside the router.
+    private readonly IHistoryRouter? _historyRouter;
+    private LegacyDriverHistoryAdapter? _legacyHistoryAdapter;
+
+    // PR 2.3 — server-level alarm-condition state machine. When non-null, every
+    // MarkAsAlarmCondition call also registers the condition with the service so the
+    // server runs the Active/Acknowledged/Inactive transitions itself instead of
+    // relying on the driver's own tracker. _conditionSinks maps conditionId →
+    // ConditionSink so service-raised transitions reach the right OPC UA AlarmCondition
+    // sibling. Legacy IAlarmSource path keeps working in parallel until PR 7.2.
+    private readonly AlarmConditionService? _alarmService;
+    private readonly Dictionary<string, ConditionSink> _conditionSinks = new(StringComparer.OrdinalIgnoreCase);
+    private EventHandler<AlarmConditionTransition>? _alarmTransitionHandler;
+
     public DriverNodeManager(IServerInternal server, ApplicationConfiguration configuration,
         IDriver driver, CapabilityInvoker invoker, ILogger<DriverNodeManager> logger,
         AuthorizationGate? authzGate = null, NodeScopeResolver? scopeResolver = null,
-        IReadable? virtualReadable = null, IReadable? scriptedAlarmReadable = null)
+        IReadable? virtualReadable = null, IReadable? scriptedAlarmReadable = null,
+        IHistoryRouter? historyRouter = null,
+        AlarmConditionService? alarmService = null)
         : base(server, configuration, namespaceUris: $"urn:OtOpcUa:{driver.DriverInstanceId}")
     {
         _driver = driver;
@@ -100,7 +123,117 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         _scopeResolver = scopeResolver;
         _virtualReadable = virtualReadable;
         _scriptedAlarmReadable = scriptedAlarmReadable;
+        _historyRouter = historyRouter;
+        _alarmService = alarmService;
         _logger = logger;
+
+        if (_alarmService is not null)
+        {
+            _alarmTransitionHandler = OnAlarmServiceTransition;
+            _alarmService.TransitionRaised += _alarmTransitionHandler;
+        }
+    }
+
+    /// <summary>
+    ///     Routes <see cref="AlarmConditionService.TransitionRaised"/> to the matching
+    ///     <see cref="ConditionSink"/> registered during <c>MarkAsAlarmCondition</c>. Translates
+    ///     <see cref="AlarmConditionTransition"/> into the legacy <see cref="AlarmEventArgs"/>
+    ///     shape the existing sink consumes — the sink's switch on <c>AlarmType</c> string
+    ///     ("Active" / "Acknowledged" / "Inactive") is preserved so PR 2.3 doesn't perturb the
+    ///     OPC UA Part 9 state mapping. Stale transitions for an untracked condition are
+    ///     silently dropped.
+    /// </summary>
+    private void OnAlarmServiceTransition(object? sender, AlarmConditionTransition t)
+    {
+        ConditionSink? sink;
+        lock (Lock)
+        {
+            _conditionSinks.TryGetValue(t.ConditionId, out sink);
+        }
+        if (sink is null) return;
+
+        var transitionName = t.Transition switch
+        {
+            AlarmStateTransition.Active => "Active",
+            AlarmStateTransition.Acknowledged => "Acknowledged",
+            AlarmStateTransition.Inactive => "Inactive",
+            _ => "Unknown",
+        };
+
+        sink.OnTransition(new AlarmEventArgs(
+            SubscriptionHandle: null!,
+            SourceNodeId: t.ConditionId,
+            ConditionId: t.ConditionId,
+            AlarmType: transitionName,
+            Message: t.Description ?? t.ConditionId,
+            Severity: MapPriorityToSeverity(t.Priority),
+            SourceTimestampUtc: t.AtUtc));
+    }
+
+    /// <summary>
+    ///     Maps the integer priority Galaxy carries on <c>.Priority</c> (typically 1-1000) to
+    ///     the four-bucket <see cref="AlarmSeverity"/> the OPC UA condition sibling consumes.
+    ///     Mirrors the legacy <c>GalaxyProxyDriver.MapSeverity</c> bucketing.
+    /// </summary>
+    private static AlarmSeverity MapPriorityToSeverity(int priority) => priority switch
+    {
+        <= 250 => AlarmSeverity.Low,
+        <= 500 => AlarmSeverity.Medium,
+        <= 800 => AlarmSeverity.High,
+        _ => AlarmSeverity.Critical,
+    };
+
+    /// <summary>
+    ///     Default <see cref="IAlarmAcknowledger"/> bound to a driver's <see cref="IWritable"/>.
+    ///     Writes the operator comment to the alarm's <c>.AckMsg</c> sub-attribute via the same
+    ///     dispatcher OnWriteValue uses so the resilience pipeline gates the call. Returns
+    ///     false when the driver doesn't implement <see cref="IWritable"/> — alarms whose
+    ///     drivers can't write are tracked but cannot be acknowledged through this path.
+    /// </summary>
+    private sealed class DriverWritableAcknowledger(
+        IWritable? writable, CapabilityInvoker invoker, string driverInstanceId) : IAlarmAcknowledger
+    {
+        public async Task<bool> WriteAckMessageAsync(
+            string ackMsgWriteRef, string comment, CancellationToken cancellationToken)
+        {
+            if (writable is null || string.IsNullOrEmpty(ackMsgWriteRef)) return false;
+
+            var request = new DriverWriteRequest(
+                FullReference: ackMsgWriteRef,
+                Value: comment ?? string.Empty);
+
+            try
+            {
+                // Ack writes are not idempotent — repeating an ack would re-trigger the
+                // driver-side acknowledgement state change. False matches the OnWriteValue
+                // default path for non-Idempotent attributes.
+                var results = await invoker.ExecuteWriteAsync(
+                    driverInstanceId,
+                    isIdempotent: false,
+                    async ct => await writable.WriteAsync(new[] { request }, ct).ConfigureAwait(false),
+                    cancellationToken).ConfigureAwait(false);
+                return results.Count > 0 && results[0].StatusCode == 0;
+            }
+            catch
+            {
+                return false;
+            }
+        }
+    }
+
+    /// <summary>
+    ///     Detach from the alarm service before the base disposes. The service is shared across
+    ///     drivers, so leaking the handler keeps a dead DriverNodeManager pinned in memory and
+    ///     dispatches transitions to a sink that's no longer wired to any OPC UA node.
+    /// </summary>
+    protected override void Dispose(bool disposing)
+    {
+        if (disposing && _alarmService is not null && _alarmTransitionHandler is not null)
+        {
+            _alarmService.TransitionRaised -= _alarmTransitionHandler;
+            _alarmTransitionHandler = null;
+        }
+        base.Dispose(disposing);
     }
 
     protected override NodeStateCollection LoadPredefinedNodes(ISystemContext context) => new();
@@ -644,7 +777,22 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 // Without this the Report fires but has no subscribers to deliver to.
                 _owner.AddRootNotifier(alarm);
 
-                return new ConditionSink(_owner, alarm);
+                var sink = new ConditionSink(_owner, alarm);
+
+                // PR 2.3 — when the server-level alarm-condition service is wired, register
+                // this condition with it so the state machine runs server-side. The sink-map
+                // entry routes future TransitionRaised events back to this OPC UA node.
+                // Conditions whose info lacks an InAlarmRef can't be observed without driver
+                // help — those still rely on the legacy IAlarmSource path until PR 7.2.
+                if (_owner._alarmService is not null && !string.IsNullOrEmpty(info.InAlarmRef))
+                {
+                    _owner._conditionSinks[FullReference] = sink;
+                    var acker = new DriverWritableAcknowledger(
+                        _owner._writable, _owner._invoker, _owner._driver.DriverInstanceId);
+                    _owner._alarmService.Track(FullReference, info, acker);
+                }
+
+                return sink;
             }
         }
 
@@ -808,29 +956,97 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
     internal bool TryGetVariable(string fullRef, out BaseDataVariableState? v)
         => _variablesByFullRef.TryGetValue(fullRef, out v!);
 
-    // ===================== HistoryRead service handlers (LMX #1, PR 38) =====================
+    // ===================== HistoryRead service handlers (LMX #1, PR 38; PR 1.3 routing) =====================
     //
-    // Wires the driver's IHistoryProvider capability (PR 35 added ReadAtTimeAsync / ReadEventsAsync
-    // alongside the PR 19 ReadRawAsync / ReadProcessedAsync) to the OPC UA HistoryRead service.
-    // CustomNodeManager2 has four protected per-kind hooks; the base dispatches to the right one
-    // based on the concrete HistoryReadDetails subtype. Each hook is sync-returning-void — the
-    // per-driver async calls are bridged via GetAwaiter().GetResult(), matching the pattern
-    // OnReadValue / OnWriteValue already use in this class so HistoryRead doesn't introduce a
-    // different sync-over-async convention.
+    // Wires HistoryRead to the server-level IHistoryRouter (PR 1.2). For each tag:
+    // (1) the router resolves the longest-matching IHistorianDataSource registration —
+    // when a server-registered source covers the namespace it wins; (2) when the router
+    // doesn't match (or no router is configured), we fall back to the driver's own
+    // IHistoryProvider capability via a thin adapter, preserving the legacy behavior tests
+    // rely on. PR 1.W will register the legacy adapter inside the router as well, at
+    // which point this fallback can be deleted.
     //
-    // Per-node routing: every HistoryReadValueId in nodesToRead has a NodeHandle in
-    // nodesToProcess; the NodeHandle's NodeId.Identifier is the driver-side full reference
-    // (set during Variable() registration) so we can dispatch straight to IHistoryProvider
-    // without a second lookup. Nodes without IHistoryProvider backing (drivers that don't
-    // implement the capability) surface BadHistoryOperationUnsupported per slot and the
-    // rest of the batch continues — same failure-isolation pattern as OnWriteValue.
-    //
-    // Continuation-point handling is pass-through only in this PR: the driver returns null
-    // from its ContinuationPoint field today so the outer result's ContinuationPoint stays
-    // empty. Full Session.SaveHistoryContinuationPoint plumbing is a follow-up when a driver
-    // actually needs paging — the dispatch shape doesn't change, only the result-population.
+    // Continuation-point handling is pass-through only: the source returns null from its
+    // ContinuationPoint today so the outer result's ContinuationPoint stays empty. Proper
+    // Session.SaveHistoryContinuationPoint plumbing is a follow-up when a source actually
+    // needs paging — the dispatch shape doesn't change, only the result-population.
 
-    private IHistoryProvider? History => _driver as IHistoryProvider;
+    /// <summary>
+    ///     Resolves the historian data source for a given driver full reference. Returns
+    ///     null when neither the router nor the legacy IHistoryProvider path can serve it.
+    /// </summary>
+    /// <param name="fullRef">
+    ///     Full reference, or null for driver-root event-history queries (event reads can
+    ///     target a notifier rather than a specific variable). Null fullRef skips router
+    ///     lookup and goes straight to the legacy fallback so today's "all events in the
+    ///     driver namespace" path keeps working.
+    /// </param>
+    private IHistorianDataSource? ResolveHistory(string? fullRef)
+    {
+        if (fullRef is not null
+            && _historyRouter?.Resolve(fullRef) is { } routed)
+        {
+            return routed;
+        }
+
+        if (_driver is IHistoryProvider legacy)
+        {
+            return _legacyHistoryAdapter ??= new LegacyDriverHistoryAdapter(legacy);
+        }
+
+        return null;
+    }
+
+    /// <summary>
+    ///     Wraps a driver's <see cref="IHistoryProvider"/> as an
+    ///     <see cref="IHistorianDataSource"/> so the four HistoryRead* methods can dispatch
+    ///     through one interface regardless of resolution path. PR 1.W's legacy
+    ///     auto-registration uses the same adapter; PR 7.2 deletes both once
+    ///     IHistoryProvider stops being a driver capability.
+    /// </summary>
+    // OTOPCUA0001 (UnwrappedCapabilityCallAnalyzer) flags every direct IHistoryProvider call
+    // that isn't lexically inside a CapabilityInvoker.ExecuteAsync lambda. The adapter's
+    // pass-throughs are direct calls — but the four HistoryRead* call sites that own the
+    // adapter ARE inside ExecuteAsync lambdas, so the wrapping is preserved at runtime.
+    // Suppress here rather than at every call site.
+#pragma warning disable OTOPCUA0001
+    private sealed class LegacyDriverHistoryAdapter(IHistoryProvider provider) : IHistorianDataSource
+    {
+        // HistoryReadResult is unqualified-ambiguous in this file (Core.Abstractions vs.
+        // Opc.Ua); fully qualify on the adapter signatures so the file's existing var-based
+        // dispatch sites stay readable.
+        public Task<Core.Abstractions.HistoryReadResult> ReadRawAsync(
+            string fullReference, DateTime startUtc, DateTime endUtc, uint maxValuesPerNode,
+            CancellationToken cancellationToken)
+            => provider.ReadRawAsync(fullReference, startUtc, endUtc, maxValuesPerNode, cancellationToken);
+
+        public Task<Core.Abstractions.HistoryReadResult> ReadProcessedAsync(
+            string fullReference, DateTime startUtc, DateTime endUtc, TimeSpan interval,
+            HistoryAggregateType aggregate, CancellationToken cancellationToken)
+            => provider.ReadProcessedAsync(fullReference, startUtc, endUtc, interval, aggregate, cancellationToken);
+
+        public Task<Core.Abstractions.HistoryReadResult> ReadAtTimeAsync(
+            string fullReference, IReadOnlyList<DateTime> timestampsUtc, CancellationToken cancellationToken)
+            => provider.ReadAtTimeAsync(fullReference, timestampsUtc, cancellationToken);
+
+        public Task<HistoricalEventsResult> ReadEventsAsync(
+            string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents,
+            CancellationToken cancellationToken)
+            => provider.ReadEventsAsync(sourceName, startUtc, endUtc, maxEvents, cancellationToken);
+
+        // Legacy IHistoryProvider has no health surface. Return an "unknown but reachable"
+        // snapshot so dashboards don't show the data source as broken.
+        public HistorianHealthSnapshot GetHealthSnapshot()
+            => new(0, 0, 0, 0, null, null, null,
+                ProcessConnectionOpen: true, EventConnectionOpen: true,
+                ActiveProcessNode: null, ActiveEventNode: null,
+                Nodes: []);
+
+        // Legacy lifecycle is the driver's responsibility — disposing the adapter must
+        // not dispose the driver out from under DriverNodeManager.
+        public void Dispose() { }
+    }
+#pragma warning restore OTOPCUA0001
 
     protected override void HistoryReadRawModified(
         ServerSystemContext context, ReadRawModifiedDetails details, TimestampsToReturn timestamps,
@@ -838,12 +1054,6 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         IList<ServiceResult> errors, List<NodeHandle> nodesToProcess,
         IDictionary<NodeId, NodeState> cache)
     {
-        if (History is null)
-        {
-            MarkAllUnsupported(nodesToProcess, results, errors);
-            return;
-        }
-
         // IsReadModified=true requests a "modifications" history (who changed the data, when
         // it was re-written). The driver side has no modifications store — surface that
         // explicitly rather than silently returning raw data, which would mislead the client.
@@ -868,6 +1078,13 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 continue;
             }
 
+            var source = ResolveHistory(fullRef);
+            if (source is null)
+            {
+                WriteUnsupported(results, errors, i);
+                continue;
+            }
+
             if (_authzGate is not null && _scopeResolver is not null)
             {
                 var historyScope = _scopeResolver.Resolve(fullRef);
@@ -883,7 +1100,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
                     ResolveHostFor(fullRef),
-                    async ct => await History.ReadRawAsync(
+                    async ct => await source.ReadRawAsync(
                         fullRef,
                         details.StartTime,
                         details.EndTime,
@@ -912,12 +1129,6 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         IList<ServiceResult> errors, List<NodeHandle> nodesToProcess,
         IDictionary<NodeId, NodeState> cache)
     {
-        if (History is null)
-        {
-            MarkAllUnsupported(nodesToProcess, results, errors);
-            return;
-        }
-
         // AggregateType is one NodeId shared across every item in the batch — map once.
         var aggregate = MapAggregate(details.AggregateType?.FirstOrDefault());
         if (aggregate is null)
@@ -930,10 +1141,6 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         for (var n = 0; n < nodesToProcess.Count; n++)
         {
             var handle = nodesToProcess[n];
-            // NodeHandle.Index points back to the slot in the outer results/errors/nodesToRead
-            // arrays. nodesToProcess is the filtered subset (just the nodes this manager
-            // claimed), so writing to results[n] lands in the wrong slot when N > 1 and nodes
-            // are interleaved across multiple node managers.
             var i = handle.Index;
             var fullRef = ResolveFullRef(handle);
             if (fullRef is null)
@@ -942,6 +1149,13 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 continue;
             }
 
+            var source = ResolveHistory(fullRef);
+            if (source is null)
+            {
+                WriteUnsupported(results, errors, i);
+                continue;
+            }
+
             if (_authzGate is not null && _scopeResolver is not null)
             {
                 var historyScope = _scopeResolver.Resolve(fullRef);
@@ -957,7 +1171,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
                     ResolveHostFor(fullRef),
-                    async ct => await History.ReadProcessedAsync(
+                    async ct => await source.ReadProcessedAsync(
                         fullRef,
                         details.StartTime,
                         details.EndTime,
@@ -987,20 +1201,10 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         IList<ServiceResult> errors, List<NodeHandle> nodesToProcess,
         IDictionary<NodeId, NodeState> cache)
     {
-        if (History is null)
-        {
-            MarkAllUnsupported(nodesToProcess, results, errors);
-            return;
-        }
-
         var requestedTimes = (IReadOnlyList<DateTime>)(details.ReqTimes?.ToArray() ?? Array.Empty<DateTime>());
         for (var n = 0; n < nodesToProcess.Count; n++)
         {
             var handle = nodesToProcess[n];
-            // NodeHandle.Index points back to the slot in the outer results/errors/nodesToRead
-            // arrays. nodesToProcess is the filtered subset (just the nodes this manager
-            // claimed), so writing to results[n] lands in the wrong slot when N > 1 and nodes
-            // are interleaved across multiple node managers.
             var i = handle.Index;
             var fullRef = ResolveFullRef(handle);
             if (fullRef is null)
@@ -1009,6 +1213,13 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 continue;
             }
 
+            var source = ResolveHistory(fullRef);
+            if (source is null)
+            {
+                WriteUnsupported(results, errors, i);
+                continue;
+            }
+
             if (_authzGate is not null && _scopeResolver is not null)
             {
                 var historyScope = _scopeResolver.Resolve(fullRef);
@@ -1024,7 +1235,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
                     ResolveHostFor(fullRef),
-                    async ct => await History.ReadAtTimeAsync(fullRef, requestedTimes, ct).ConfigureAwait(false),
+                    async ct => await source.ReadAtTimeAsync(fullRef, requestedTimes, ct).ConfigureAwait(false),
                     CancellationToken.None).AsTask().GetAwaiter().GetResult();
 
                 WriteResult(results, errors, i, StatusCodes.Good,
@@ -1048,34 +1259,30 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         IList<ServiceResult> errors, List<NodeHandle> nodesToProcess,
         IDictionary<NodeId, NodeState> cache)
     {
-        if (History is null)
-        {
-            MarkAllUnsupported(nodesToProcess, results, errors);
-            return;
-        }
-
         // SourceName filter extraction is deferred — EventFilter SelectClauses + WhereClause
-        // handling is a dedicated concern (proper per-select-clause Variant population + where
-        // filter evaluation). This PR treats the event query as "all events in range for the
-        // node's source" and populates only the standard BaseEventType fields. Richer filter
-        // handling is a follow-up; clients issuing empty/default filters get the right answer
-        // today which covers the common alarm-history browse case.
+        // handling is a dedicated concern. This PR treats the event query as "all events in
+        // range for the node's source" and populates only the standard BaseEventType fields.
         var maxEvents = (int)details.NumValuesPerNode;
         if (maxEvents <= 0) maxEvents = 1000;
 
         for (var n = 0; n < nodesToProcess.Count; n++)
         {
             var handle = nodesToProcess[n];
-            // NodeHandle.Index points back to the slot in the outer results/errors/nodesToRead
-            // arrays. nodesToProcess is the filtered subset (just the nodes this manager
-            // claimed), so writing to results[n] lands in the wrong slot when N > 1 and nodes
-            // are interleaved across multiple node managers.
             var i = handle.Index;
             // Event history queries may target a notifier object (e.g. the driver-root folder)
-            // rather than a specific variable — in that case we pass sourceName=null to mean
-            // "all sources in the driver's namespace" per the IHistoryProvider contract.
+            // rather than a specific variable — in that case fullRef is null and we pass
+            // sourceName=null to the source meaning "all sources in this source's namespace."
             var fullRef = ResolveFullRef(handle);
 
+            // ResolveHistory tolerates null fullRef — for notifier queries the router is
+            // skipped and the legacy fallback handles "all sources" reads.
+            var source = ResolveHistory(fullRef);
+            if (source is null)
+            {
+                WriteUnsupported(results, errors, i);
+                continue;
+            }
+
             // fullRef is null for event-history queries that target a notifier (driver root).
             // Those are cluster-wide reads + need a different scope shape; skip the gate here
             // and let the driver-level authz handle them. Non-null path gets per-node gating.
@@ -1094,7 +1301,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
                     fullRef is null ? _driver.DriverInstanceId : ResolveHostFor(fullRef),
-                    async ct => await History.ReadEventsAsync(
+                    async ct => await source.ReadEventsAsync(
                         sourceName: fullRef,
                         startUtc: details.StartTime,
                         endUtc: details.EndTime,

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

@@ -5,6 +5,8 @@ using ZB.MOM.WW.OtOpcUa.Configuration.LocalCache;
 using ZB.MOM.WW.OtOpcUa.Core.Hosting;
 using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
 using ZB.MOM.WW.OtOpcUa.Core.Resilience;
+using ZB.MOM.WW.OtOpcUa.Server.Alarms;
+using ZB.MOM.WW.OtOpcUa.Server.History;
 using ZB.MOM.WW.OtOpcUa.Server.Observability;
 using ZB.MOM.WW.OtOpcUa.Server.Security;
 
@@ -40,6 +42,12 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
     private ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? _virtualReadable;
     private ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? _scriptedAlarmReadable;
 
+    // PR 1+2.W — server-level singletons. Threaded through to OtOpcUaServer + every
+    // DriverNodeManager. Default null preserves existing test construction sites that
+    // don't opt into the new server-side history routing or alarm-condition state machine.
+    private readonly IHistoryRouter? _historyRouter;
+    private readonly AlarmConditionService? _alarmConditionService;
+
     private readonly ILoggerFactory _loggerFactory;
     private readonly ILogger<OpcUaApplicationHost> _logger;
     private ApplicationInstance? _application;
@@ -57,7 +65,9 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
         Func<string, string?>? resilienceConfigLookup = null,
         Func<string, ZB.MOM.WW.OtOpcUa.Core.OpcUa.EquipmentNamespaceContent?>? equipmentContentLookup = null,
         ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? virtualReadable = null,
-        ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? scriptedAlarmReadable = null)
+        ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? scriptedAlarmReadable = null,
+        IHistoryRouter? historyRouter = null,
+        AlarmConditionService? alarmConditionService = null)
     {
         _options = options;
         _driverHost = driverHost;
@@ -71,6 +81,8 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
         _equipmentContentLookup = equipmentContentLookup;
         _virtualReadable = virtualReadable;
         _scriptedAlarmReadable = scriptedAlarmReadable;
+        _historyRouter = historyRouter;
+        _alarmConditionService = alarmConditionService;
         _loggerFactory = loggerFactory;
         _logger = logger;
     }
@@ -136,7 +148,8 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
             authzGate: _authzGate, scopeResolver: _scopeResolver,
             tierLookup: _tierLookup, resilienceConfigLookup: _resilienceConfigLookup,
             virtualReadable: _virtualReadable, scriptedAlarmReadable: _scriptedAlarmReadable,
-            anonymousRoles: _options.AnonymousRoles);
+            anonymousRoles: _options.AnonymousRoles,
+            historyRouter: _historyRouter, alarmConditionService: _alarmConditionService);
         await _application.Start(_server).ConfigureAwait(false);
 
         _logger.LogInformation("OPC UA server started — endpoint={Endpoint} driverCount={Count}",

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

@@ -6,6 +6,8 @@ using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Core.Hosting;
 using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
 using ZB.MOM.WW.OtOpcUa.Core.Resilience;
+using ZB.MOM.WW.OtOpcUa.Server.Alarms;
+using ZB.MOM.WW.OtOpcUa.Server.History;
 using ZB.MOM.WW.OtOpcUa.Server.Security;
 
 namespace ZB.MOM.WW.OtOpcUa.Server.OpcUa;
@@ -34,6 +36,13 @@ public sealed class OtOpcUaServer : StandardServer
     private readonly IReadable? _virtualReadable;
     private readonly IReadable? _scriptedAlarmReadable;
 
+    // PR 1+2.W — server-level singletons shared across every DriverNodeManager.
+    // Null when the deployment hasn't opted into the new server-side history routing /
+    // server-side alarm-condition state machine; DriverNodeManager falls back to the
+    // legacy per-driver IHistoryProvider + IAlarmSource paths in that case.
+    private readonly IHistoryRouter? _historyRouter;
+    private readonly AlarmConditionService? _alarmConditionService;
+
     /// <summary>
     ///     Roles granted to anonymous sessions. When non-empty, <see cref="OnImpersonateUser"/>
     ///     wraps <c>AnonymousIdentityToken</c> in a <see cref="RoleBasedIdentity"/> carrying
@@ -57,7 +66,9 @@ public sealed class OtOpcUaServer : StandardServer
         Func<string, string?>? resilienceConfigLookup = null,
         IReadable? virtualReadable = null,
         IReadable? scriptedAlarmReadable = null,
-        IReadOnlyList<string>? anonymousRoles = null)
+        IReadOnlyList<string>? anonymousRoles = null,
+        IHistoryRouter? historyRouter = null,
+        AlarmConditionService? alarmConditionService = null)
     {
         _driverHost = driverHost;
         _authenticator = authenticator;
@@ -69,6 +80,8 @@ public sealed class OtOpcUaServer : StandardServer
         _virtualReadable = virtualReadable;
         _scriptedAlarmReadable = scriptedAlarmReadable;
         _anonymousRoles = anonymousRoles ?? [];
+        _historyRouter = historyRouter;
+        _alarmConditionService = alarmConditionService;
         _loggerFactory = loggerFactory;
     }
 
@@ -102,7 +115,14 @@ public sealed class OtOpcUaServer : StandardServer
             var invoker = new CapabilityInvoker(_pipelineBuilder, driver.DriverInstanceId, () => options, driver.DriverType);
             var manager = new DriverNodeManager(server, configuration, driver, invoker, logger,
                 authzGate: _authzGate, scopeResolver: _scopeResolver,
-                virtualReadable: _virtualReadable, scriptedAlarmReadable: _scriptedAlarmReadable);
+                virtualReadable: _virtualReadable, scriptedAlarmReadable: _scriptedAlarmReadable,
+                historyRouter: _historyRouter, alarmService: _alarmConditionService);
+
+            // The router stays empty after PR 1+2.W — DriverNodeManager's internal
+            // LegacyDriverHistoryAdapter handles every driver that still implements
+            // IHistoryProvider. PR 3.W will register the Wonderware sidecar as a router
+            // source; PR 7.2 retires the legacy fallback entirely.
+
             _driverNodeManagers.Add(manager);
         }
 

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

@@ -17,6 +17,8 @@ using ZB.MOM.WW.OtOpcUa.Driver.Modbus;
 using ZB.MOM.WW.OtOpcUa.Driver.S7;
 using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
 using ZB.MOM.WW.OtOpcUa.Server;
+using ZB.MOM.WW.OtOpcUa.Server.Alarms;
+using ZB.MOM.WW.OtOpcUa.Server.History;
 using ZB.MOM.WW.OtOpcUa.Server.Hosting;
 using ZB.MOM.WW.OtOpcUa.Server.OpcUa;
 using ZB.MOM.WW.OtOpcUa.Server.Phase7;
@@ -137,6 +139,14 @@ builder.Services.AddScoped<EquipmentNamespaceContentLoader>();
 // to ACL enforcement accidentally on upgrade.
 builder.Services.AddSingleton<AuthorizationBootstrap>();
 
+// PR 1+2.W — server-level history routing + alarm-condition state machine. Singletons
+// shared across every DriverNodeManager. The router stays empty after this PR;
+// PR 3.W registers the Wonderware historian sidecar as a router source. The alarm
+// service runs the Active/Acknowledged/Inactive state machine for any driver that
+// declares alarms via AlarmConditionInfo's sub-attribute refs.
+builder.Services.AddSingleton<IHistoryRouter, HistoryRouter>();
+builder.Services.AddSingleton<AlarmConditionService>();
+
 builder.Services.AddSingleton<OpcUaApplicationHost>(sp =>
 {
     var registry = sp.GetRequiredService<DriverEquipmentContentRegistry>();
@@ -146,7 +156,9 @@ builder.Services.AddSingleton<OpcUaApplicationHost>(sp =>
         sp.GetRequiredService<IUserAuthenticator>(),
         sp.GetRequiredService<ILoggerFactory>(),
         sp.GetRequiredService<ILogger<OpcUaApplicationHost>>(),
-        equipmentContentLookup: registry.Get);
+        equipmentContentLookup: registry.Get,
+        historyRouter: sp.GetRequiredService<IHistoryRouter>(),
+        alarmConditionService: sp.GetRequiredService<AlarmConditionService>());
 });
 builder.Services.AddHostedService<OpcUaServerService>();
 

tests/ZB.MOM.WW.OtOpcUa.Admin.Tests/TagServiceTests.cs

@@ -0,0 +1,146 @@
+using Microsoft.EntityFrameworkCore;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Admin.Services;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+
+namespace ZB.MOM.WW.OtOpcUa.Admin.Tests;
+
+/// <summary>
+///     #155 — TagService CRUD round-trip coverage. Mirrors the EquipmentService test shape;
+///     uses EF Core InMemory so no SQL Server is required.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class TagServiceTests
+{
+    [Fact]
+    public async Task Create_And_List_Surfaces_The_Tag()
+    {
+        using var ctx = NewContext();
+        var svc = new TagService(ctx);
+
+        var created = await svc.CreateAsync(draftId: 1, NewTag("Temp"), TestContext.Current.CancellationToken);
+        created.TagId.ShouldNotBeNullOrEmpty();
+        created.GenerationId.ShouldBe(1);
+
+        var list = await svc.ListAsync(1, ct: TestContext.Current.CancellationToken);
+        list.Count.ShouldBe(1);
+        list[0].Name.ShouldBe("Temp");
+    }
+
+    [Fact]
+    public async Task List_Filters_By_DriverInstance()
+    {
+        using var ctx = NewContext();
+        var svc = new TagService(ctx);
+        await svc.CreateAsync(1, NewTag("a", driver: "drv-1"), TestContext.Current.CancellationToken);
+        await svc.CreateAsync(1, NewTag("b", driver: "drv-2"), TestContext.Current.CancellationToken);
+        await svc.CreateAsync(1, NewTag("c", driver: "drv-1"), TestContext.Current.CancellationToken);
+
+        var d1 = await svc.ListAsync(1, driverInstanceId: "drv-1", ct: TestContext.Current.CancellationToken);
+        d1.Count.ShouldBe(2);
+        d1.Select(t => t.Name).ShouldBe(new[] { "a", "c" }, ignoreOrder: true);
+    }
+
+    [Fact]
+    public async Task Update_Persists_Editable_Fields()
+    {
+        using var ctx = NewContext();
+        var svc = new TagService(ctx);
+        var t = await svc.CreateAsync(1, NewTag("Original"), TestContext.Current.CancellationToken);
+
+        t.Name = "Renamed";
+        t.DataType = "Float";
+        t.AccessLevel = TagAccessLevel.ReadWrite;
+        t.TagConfig = "{\"addressString\":\"40001:F\"}";
+        await svc.UpdateAsync(t, TestContext.Current.CancellationToken);
+
+        var fresh = (await svc.ListAsync(1, ct: TestContext.Current.CancellationToken))[0];
+        fresh.Name.ShouldBe("Renamed");
+        fresh.DataType.ShouldBe("Float");
+        fresh.AccessLevel.ShouldBe(TagAccessLevel.ReadWrite);
+        fresh.TagConfig.ShouldContain("40001:F");
+    }
+
+    [Fact]
+    public async Task TagConfig_With_Advanced_Modbus_Fields_RoundTrips_Through_Factory()
+    {
+        // #156 — TagsTab serializes advanced fields (deadband / unitId / coalesceProhibited)
+        // into TagConfig as a structured JSON object alongside addressString. Confirm the
+        // shape survives a DB round-trip AND that ModbusDriverFactoryExtensions.BuildTag's
+        // JSON consumer accepts it. If the field names drift between the UI and the factory,
+        // this test catches it before users do.
+        using var ctx = NewContext();
+        var svc = new TagService(ctx);
+
+        var advancedConfig = System.Text.Json.JsonSerializer.Serialize(new
+        {
+            addressString = "40001:F:CDAB",
+            deadband = 0.5,
+            unitId = 7,
+            coalesceProhibited = true,
+        });
+        var t = NewTag("Tank");
+        t.TagConfig = advancedConfig;
+        await svc.CreateAsync(1, t, TestContext.Current.CancellationToken);
+
+        var fresh = (await svc.ListAsync(1, ct: TestContext.Current.CancellationToken)).Single();
+        fresh.TagConfig.ShouldContain("addressString");
+        fresh.TagConfig.ShouldContain("deadband");
+        fresh.TagConfig.ShouldContain("unitId");
+        fresh.TagConfig.ShouldContain("coalesceProhibited");
+
+        // Build the wrapping driver-config JSON the factory consumes (one tag, the structured
+        // config above as its TagConfig), then construct a driver from it. If any field name
+        // doesn't match the DTO, BuildTag throws here.
+        var driverConfig = System.Text.Json.JsonSerializer.Serialize(new
+        {
+            host = "127.0.0.1",
+            tags = new[]
+            {
+                new
+                {
+                    name = "Tank",
+                    addressString = "40001:F:CDAB",
+                    deadband = 0.5,
+                    unitId = (byte)7,
+                    coalesceProhibited = true,
+                },
+            },
+        });
+        Should.NotThrow(() => ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusDriverFactoryExtensions.CreateInstance(
+            "advanced-rt", driverConfig));
+    }
+
+    [Fact]
+    public async Task Delete_Removes_The_Row()
+    {
+        using var ctx = NewContext();
+        var svc = new TagService(ctx);
+        var t = await svc.CreateAsync(1, NewTag("Doomed"), TestContext.Current.CancellationToken);
+
+        await svc.DeleteAsync(t.TagRowId, TestContext.Current.CancellationToken);
+
+        (await svc.ListAsync(1, ct: TestContext.Current.CancellationToken)).ShouldBeEmpty();
+    }
+
+    private static Tag NewTag(string name, string driver = "drv-1") => new()
+    {
+        TagId = string.Empty,            // CreateAsync auto-assigns
+        DriverInstanceId = driver,
+        Name = name,
+        DataType = "Int32",
+        AccessLevel = TagAccessLevel.Read,
+        TagConfig = "{}",
+    };
+
+    private static OtOpcUaConfigDbContext NewContext()
+    {
+        var opts = new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
+            .UseInMemoryDatabase(Guid.NewGuid().ToString())
+            .Options;
+        return new OtOpcUaConfigDbContext(opts);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/Alarms/AlarmConditionInfoTests.cs

@@ -0,0 +1,100 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.Alarms;
+
+/// <summary>
+///     Contract tests for the <see cref="AlarmConditionInfo"/> record extension added in PR 2.1.
+///     Five sub-attribute references (InAlarmRef, PriorityRef, DescAttrNameRef, AckedRef,
+///     AckMsgWriteRef) carry the driver-side tag references the server-level alarm-condition
+///     service uses to subscribe to live alarm-state attributes and route ack writes.
+/// </summary>
+public sealed class AlarmConditionInfoTests
+{
+    [Fact]
+    public void LegacyThreeArgConstructor_StillCompiles_AndDefaultsRefsToNull()
+    {
+        var info = new AlarmConditionInfo(
+            SourceName: "Tank.HiHi",
+            InitialSeverity: AlarmSeverity.High,
+            InitialDescription: "High-high alarm");
+
+        info.SourceName.ShouldBe("Tank.HiHi");
+        info.InitialSeverity.ShouldBe(AlarmSeverity.High);
+        info.InitialDescription.ShouldBe("High-high alarm");
+        info.InAlarmRef.ShouldBeNull();
+        info.PriorityRef.ShouldBeNull();
+        info.DescAttrNameRef.ShouldBeNull();
+        info.AckedRef.ShouldBeNull();
+        info.AckMsgWriteRef.ShouldBeNull();
+    }
+
+    [Fact]
+    public void FullConstructor_PopulatesAllFiveSubAttributeRefs()
+    {
+        var info = new AlarmConditionInfo(
+            SourceName: "Tank1.HiAlarm",
+            InitialSeverity: AlarmSeverity.Medium,
+            InitialDescription: "Tank level high",
+            InAlarmRef: "Tank1.HiAlarm.InAlarm",
+            PriorityRef: "Tank1.HiAlarm.Priority",
+            DescAttrNameRef: "Tank1.HiAlarm.DescAttrName",
+            AckedRef: "Tank1.HiAlarm.Acked",
+            AckMsgWriteRef: "Tank1.HiAlarm.AckMsg");
+
+        info.InAlarmRef.ShouldBe("Tank1.HiAlarm.InAlarm");
+        info.PriorityRef.ShouldBe("Tank1.HiAlarm.Priority");
+        info.DescAttrNameRef.ShouldBe("Tank1.HiAlarm.DescAttrName");
+        info.AckedRef.ShouldBe("Tank1.HiAlarm.Acked");
+        info.AckMsgWriteRef.ShouldBe("Tank1.HiAlarm.AckMsg");
+    }
+
+    [Fact]
+    public void RecordEquality_ComparesAllEightFields()
+    {
+        var a = new AlarmConditionInfo(
+            "T.Alarm", AlarmSeverity.Low, "desc",
+            "T.Alarm.InAlarm", "T.Alarm.Priority", "T.Alarm.DescAttrName",
+            "T.Alarm.Acked", "T.Alarm.AckMsg");
+
+        var b = new AlarmConditionInfo(
+            "T.Alarm", AlarmSeverity.Low, "desc",
+            "T.Alarm.InAlarm", "T.Alarm.Priority", "T.Alarm.DescAttrName",
+            "T.Alarm.Acked", "T.Alarm.AckMsg");
+
+        a.ShouldBe(b);
+    }
+
+    [Fact]
+    public void RecordEquality_DistinctWhenAnyRefDiffers()
+    {
+        var baseInfo = new AlarmConditionInfo(
+            "T.Alarm", AlarmSeverity.Low, "desc",
+            InAlarmRef: "T.Alarm.InAlarm");
+
+        var differingAckRef = baseInfo with { AckedRef = "T.Alarm.Acked" };
+
+        baseInfo.ShouldNotBe(differingAckRef);
+    }
+
+    [Fact]
+    public void WithExpression_AllowsPartialUpdates()
+    {
+        var legacy = new AlarmConditionInfo("S", AlarmSeverity.Medium, null);
+
+        var enriched = legacy with
+        {
+            InAlarmRef = "S.InAlarm",
+            AckedRef = "S.Acked",
+            AckMsgWriteRef = "S.AckMsg",
+        };
+
+        enriched.SourceName.ShouldBe("S");
+        enriched.InAlarmRef.ShouldBe("S.InAlarm");
+        enriched.PriorityRef.ShouldBeNull();
+        enriched.DescAttrNameRef.ShouldBeNull();
+        enriched.AckedRef.ShouldBe("S.Acked");
+        enriched.AckMsgWriteRef.ShouldBe("S.AckMsg");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/Historian/IHistorianDataSourceContractTests.cs

@@ -0,0 +1,121 @@
+using System.Reflection;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.Historian;
+
+/// <summary>
+///     Structural contract tests for the historian data-source surface added in PR 1.1.
+///     Asserts the type shape — implementations are tested in their own projects.
+/// </summary>
+public sealed class IHistorianDataSourceContractTests
+{
+    [Fact]
+    public void Interface_LivesInRootNamespace()
+    {
+        typeof(IHistorianDataSource).Namespace
+            .ShouldBe("ZB.MOM.WW.OtOpcUa.Core.Abstractions");
+    }
+
+    [Fact]
+    public void Interface_IsPublic()
+    {
+        typeof(IHistorianDataSource).IsPublic.ShouldBeTrue();
+        typeof(IHistorianDataSource).IsInterface.ShouldBeTrue();
+    }
+
+    [Fact]
+    public void Interface_ExtendsIDisposable()
+    {
+        typeof(IDisposable).IsAssignableFrom(typeof(IHistorianDataSource))
+            .ShouldBeTrue("data sources own backend connections; the server disposes them on shutdown");
+    }
+
+    [Theory]
+    [InlineData("ReadRawAsync", typeof(Task<HistoryReadResult>))]
+    [InlineData("ReadProcessedAsync", typeof(Task<HistoryReadResult>))]
+    [InlineData("ReadAtTimeAsync", typeof(Task<HistoryReadResult>))]
+    [InlineData("ReadEventsAsync", typeof(Task<HistoricalEventsResult>))]
+    public void ReadMethods_ReturnExpectedTaskShape(string methodName, Type expectedReturnType)
+    {
+        var method = typeof(IHistorianDataSource).GetMethod(methodName);
+        method.ShouldNotBeNull();
+        method!.ReturnType.ShouldBe(expectedReturnType);
+    }
+
+    [Fact]
+    public void GetHealthSnapshot_IsSynchronous()
+    {
+        var method = typeof(IHistorianDataSource).GetMethod("GetHealthSnapshot");
+        method.ShouldNotBeNull();
+        method!.ReturnType.ShouldBe(typeof(HistorianHealthSnapshot));
+    }
+
+    [Fact]
+    public void HealthSnapshot_AcceptsEmptyClusterNodeList()
+    {
+        var snapshot = new HistorianHealthSnapshot(
+            TotalQueries: 0,
+            TotalSuccesses: 0,
+            TotalFailures: 0,
+            ConsecutiveFailures: 0,
+            LastSuccessTime: null,
+            LastFailureTime: null,
+            LastError: null,
+            ProcessConnectionOpen: false,
+            EventConnectionOpen: false,
+            ActiveProcessNode: null,
+            ActiveEventNode: null,
+            Nodes: Array.Empty<HistorianClusterNodeState>());
+
+        snapshot.Nodes.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void HealthSnapshot_PreservesClusterNodes()
+    {
+        var node = new HistorianClusterNodeState(
+            Name: "hist-01",
+            IsHealthy: true,
+            CooldownUntil: null,
+            FailureCount: 0,
+            LastError: null,
+            LastFailureTime: null);
+
+        var snapshot = new HistorianHealthSnapshot(
+            TotalQueries: 5,
+            TotalSuccesses: 5,
+            TotalFailures: 0,
+            ConsecutiveFailures: 0,
+            LastSuccessTime: new DateTime(2026, 4, 29, 12, 0, 0, DateTimeKind.Utc),
+            LastFailureTime: null,
+            LastError: null,
+            ProcessConnectionOpen: true,
+            EventConnectionOpen: true,
+            ActiveProcessNode: "hist-01",
+            ActiveEventNode: "hist-01",
+            Nodes: new[] { node });
+
+        snapshot.Nodes.Count.ShouldBe(1);
+        snapshot.Nodes[0].ShouldBe(node);
+    }
+
+    [Fact]
+    public void ClusterNodeState_RecordEqualityByValue()
+    {
+        var a = new HistorianClusterNodeState("hist-01", true, null, 0, null, null);
+        var b = new HistorianClusterNodeState("hist-01", true, null, 0, null, null);
+
+        a.ShouldBe(b);
+    }
+
+    [Fact]
+    public void ClusterNodeState_DistinctByAnyField()
+    {
+        var healthy = new HistorianClusterNodeState("hist-01", true, null, 0, null, null);
+        var unhealthy = new HistorianClusterNodeState("hist-01", false, null, 1, "boom", null);
+
+        healthy.ShouldNotBe(unhealthy);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/HistorianWiringTests.cs

@@ -6,7 +6,7 @@ using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Sta;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/HistoryReadAtTimeTests.cs

@@ -8,7 +8,7 @@ using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Sta;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/HistoryReadEventsTests.cs

@@ -6,7 +6,7 @@ using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Sta;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/HistoryReadProcessedTests.cs

@@ -7,7 +7,7 @@ using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Sta;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;

tests/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/Backend/HistorianClusterEndpointPickerTests.cs

@@ -2,7 +2,7 @@ using System;
 using System.Linq;
 using Shouldly;
 using Xunit;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests
 {

tests/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/Backend/HistorianQualityMapperTests.cs

@@ -1,6 +1,6 @@
 using Shouldly;
 using Xunit;
-using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests;
 

tests/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/Ipc/PipeRoundTripTests.cs

@@ -0,0 +1,284 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+using Serilog;
+using Serilog.Core;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;
+using SidecarHistorianEventDto = ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc.HistorianEventDto;
+using BackendHistorianEventDto = ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend.HistorianEventDto;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests.Ipc;
+
+/// <summary>
+///     Round-trip tests for the sidecar pipe contract added in PR 3.3. Each scenario serializes
+///     a Request through the wire framing, dispatches via <see cref="HistorianFrameHandler"/>
+///     against a fake historian, and asserts the returned Reply round-trips with the expected
+///     content. No real named pipe is opened — the framing is exercised over a back-to-back
+///     <see cref="MemoryStream"/> pair so tests stay fast and platform-independent.
+/// </summary>
+public sealed class PipeRoundTripTests
+{
+    private static readonly ILogger Quiet = Logger.None;
+
+    private sealed class FakeHistorian : IHistorianDataSource
+    {
+        public List<HistorianSample> RawSamples { get; set; } = new();
+        public List<HistorianAggregateSample> AggregateSamples { get; set; } = new();
+        public List<HistorianSample> AtTimeSamples { get; set; } = new();
+        public List<BackendHistorianEventDto> Events { get; set; } = new();
+        public Exception? ThrowFromRead { get; set; }
+
+        public Task<List<HistorianSample>> ReadRawAsync(string tagName, DateTime startTime, DateTime endTime, int maxValues, CancellationToken ct = default)
+        {
+            if (ThrowFromRead is not null) throw ThrowFromRead;
+            return Task.FromResult(RawSamples);
+        }
+
+        public Task<List<HistorianAggregateSample>> ReadAggregateAsync(string tagName, DateTime startTime, DateTime endTime, double intervalMs, string aggregateColumn, CancellationToken ct = default)
+            => Task.FromResult(AggregateSamples);
+
+        public Task<List<HistorianSample>> ReadAtTimeAsync(string tagName, DateTime[] timestamps, CancellationToken ct = default)
+            => Task.FromResult(AtTimeSamples);
+
+        public Task<List<BackendHistorianEventDto>> ReadEventsAsync(string? sourceName, DateTime startTime, DateTime endTime, int maxEvents, CancellationToken ct = default)
+            => Task.FromResult(Events);
+
+        public HistorianHealthSnapshot GetHealthSnapshot() => new();
+
+        public void Dispose() { }
+    }
+
+    private sealed class FakeAlarmWriter : IAlarmEventWriter
+    {
+        public List<AlarmHistorianEventDto> Received { get; } = new();
+        public Func<AlarmHistorianEventDto, bool> Decide { get; set; } = _ => true;
+
+        public Task<bool[]> WriteAsync(AlarmHistorianEventDto[] events, CancellationToken cancellationToken)
+        {
+            Received.AddRange(events);
+            var result = new bool[events.Length];
+            for (var i = 0; i < events.Length; i++) result[i] = Decide(events[i]);
+            return Task.FromResult(result);
+        }
+    }
+
+    /// <summary>
+    ///     Drives one round trip: serialize <paramref name="request"/>, run the handler,
+    ///     read the reply frame, deserialize it. Returns the reply.
+    /// </summary>
+    private static async Task<TReply> RoundTripAsync<TRequest, TReply>(
+        MessageKind requestKind,
+        MessageKind expectedReplyKind,
+        TRequest request,
+        IFrameHandler handler)
+    {
+        // Build the request body the same way FrameWriter would, but feed it directly into
+        // the handler's Handle method (the pipe server has already read the kind + body
+        // before handing them to the handler).
+        var requestBody = MessagePackSerializer.Serialize(request);
+
+        using var stream = new MemoryStream();
+        using var writer = new FrameWriter(stream, leaveOpen: true);
+
+        await handler.HandleAsync(requestKind, requestBody, writer, CancellationToken.None);
+
+        stream.Position = 0;
+        using var reader = new FrameReader(stream, leaveOpen: true);
+        var frame = await reader.ReadFrameAsync(CancellationToken.None);
+        frame.ShouldNotBeNull();
+        frame!.Value.Kind.ShouldBe(expectedReplyKind);
+        return MessagePackSerializer.Deserialize<TReply>(frame.Value.Body);
+    }
+
+    [Fact]
+    public async Task ReadRaw_RoundTripsSamples()
+    {
+        var historian = new FakeHistorian();
+        historian.RawSamples.Add(new HistorianSample { Value = 42.0, Quality = 192, TimestampUtc = new DateTime(2026, 4, 29, 12, 0, 0, DateTimeKind.Utc) });
+        historian.RawSamples.Add(new HistorianSample { Value = 43.5, Quality = 192, TimestampUtc = new DateTime(2026, 4, 29, 12, 0, 1, DateTimeKind.Utc) });
+
+        var handler = new HistorianFrameHandler(historian, Quiet);
+        var reply = await RoundTripAsync<ReadRawRequest, ReadRawReply>(
+            MessageKind.ReadRawRequest, MessageKind.ReadRawReply,
+            new ReadRawRequest
+            {
+                TagName = "Tank.Level",
+                StartUtcTicks = new DateTime(2026, 4, 29, 0, 0, 0, DateTimeKind.Utc).Ticks,
+                EndUtcTicks = new DateTime(2026, 4, 30, 0, 0, 0, DateTimeKind.Utc).Ticks,
+                MaxValues = 100,
+                CorrelationId = "corr-1",
+            }, handler);
+
+        reply.Success.ShouldBeTrue();
+        reply.Error.ShouldBeNull();
+        reply.CorrelationId.ShouldBe("corr-1");
+        reply.Samples.Length.ShouldBe(2);
+        reply.Samples[0].Quality.ShouldBe((byte)192);
+        reply.Samples[0].TimestampUtcTicks.ShouldBe(new DateTime(2026, 4, 29, 12, 0, 0, DateTimeKind.Utc).Ticks);
+        reply.Samples[0].ValueBytes.ShouldNotBeNull();
+        MessagePackSerializer.Deserialize<double>(reply.Samples[0].ValueBytes!).ShouldBe(42.0);
+    }
+
+    [Fact]
+    public async Task ReadRaw_FailureSurfacesAsErrorReply()
+    {
+        var historian = new FakeHistorian { ThrowFromRead = new InvalidOperationException("boom") };
+        var handler = new HistorianFrameHandler(historian, Quiet);
+        var reply = await RoundTripAsync<ReadRawRequest, ReadRawReply>(
+            MessageKind.ReadRawRequest, MessageKind.ReadRawReply,
+            new ReadRawRequest { TagName = "Tag", CorrelationId = "fail-1" }, handler);
+
+        reply.Success.ShouldBeFalse();
+        reply.Error.ShouldBe("boom");
+        reply.CorrelationId.ShouldBe("fail-1");
+        reply.Samples.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public async Task ReadProcessed_RoundTripsBuckets()
+    {
+        var historian = new FakeHistorian();
+        historian.AggregateSamples.Add(new HistorianAggregateSample { Value = 50.0, TimestampUtc = new DateTime(2026, 4, 29, 0, 0, 0, DateTimeKind.Utc) });
+        historian.AggregateSamples.Add(new HistorianAggregateSample { Value = null, TimestampUtc = new DateTime(2026, 4, 29, 0, 1, 0, DateTimeKind.Utc) });
+
+        var handler = new HistorianFrameHandler(historian, Quiet);
+        var reply = await RoundTripAsync<ReadProcessedRequest, ReadProcessedReply>(
+            MessageKind.ReadProcessedRequest, MessageKind.ReadProcessedReply,
+            new ReadProcessedRequest { TagName = "Tank.Level", IntervalMs = 60000, AggregateColumn = "Average", CorrelationId = "p-1" },
+            handler);
+
+        reply.Success.ShouldBeTrue();
+        reply.Buckets.Length.ShouldBe(2);
+        reply.Buckets[0].Value.ShouldBe(50.0);
+        reply.Buckets[1].Value.ShouldBeNull(); // unavailable bucket
+    }
+
+    [Fact]
+    public async Task ReadAtTime_RoundTripsSamples()
+    {
+        var historian = new FakeHistorian();
+        historian.AtTimeSamples.Add(new HistorianSample { Value = 7, Quality = 192, TimestampUtc = new DateTime(2026, 4, 29, 0, 0, 0, DateTimeKind.Utc) });
+
+        var handler = new HistorianFrameHandler(historian, Quiet);
+        var reply = await RoundTripAsync<ReadAtTimeRequest, ReadAtTimeReply>(
+            MessageKind.ReadAtTimeRequest, MessageKind.ReadAtTimeReply,
+            new ReadAtTimeRequest
+            {
+                TagName = "Tank.Level",
+                TimestampsUtcTicks = new[] { new DateTime(2026, 4, 29, 0, 0, 0, DateTimeKind.Utc).Ticks },
+                CorrelationId = "t-1",
+            }, handler);
+
+        reply.Success.ShouldBeTrue();
+        reply.Samples.Length.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task ReadEvents_RoundTripsEvents()
+    {
+        var historian = new FakeHistorian();
+        var eid = Guid.Parse("11111111-1111-1111-1111-111111111111");
+        historian.Events.Add(new BackendHistorianEventDto
+        {
+            Id = eid,
+            Source = "Tank.HiHi",
+            EventTime = new DateTime(2026, 4, 29, 1, 0, 0, DateTimeKind.Utc),
+            ReceivedTime = new DateTime(2026, 4, 29, 1, 0, 1, DateTimeKind.Utc),
+            DisplayText = "Level high-high",
+            Severity = 800,
+        });
+
+        var handler = new HistorianFrameHandler(historian, Quiet);
+        var reply = await RoundTripAsync<ReadEventsRequest, ReadEventsReply>(
+            MessageKind.ReadEventsRequest, MessageKind.ReadEventsReply,
+            new ReadEventsRequest { SourceName = "Tank.HiHi", MaxEvents = 100, CorrelationId = "e-1" },
+            handler);
+
+        reply.Success.ShouldBeTrue();
+        reply.Events.Length.ShouldBe(1);
+        reply.Events[0].EventId.ShouldBe(eid.ToString());
+        reply.Events[0].Source.ShouldBe("Tank.HiHi");
+        reply.Events[0].DisplayText.ShouldBe("Level high-high");
+        reply.Events[0].Severity.ShouldBe((ushort)800);
+    }
+
+    [Fact]
+    public async Task WriteAlarmEvents_RoutesToWriter_AndReturnsPerEventStatus()
+    {
+        var historian = new FakeHistorian();
+        var alarmWriter = new FakeAlarmWriter
+        {
+            // Simulate "second event fails" to verify per-event status flows through.
+            Decide = e => e.EventId != "ev-2",
+        };
+        var handler = new HistorianFrameHandler(historian, Quiet, alarmWriter);
+
+        var request = new WriteAlarmEventsRequest
+        {
+            CorrelationId = "wa-1",
+            Events = new[]
+            {
+                new AlarmHistorianEventDto { EventId = "ev-1", SourceName = "Tank.HiHi", AlarmType = "Active",     Severity = 800, EventTimeUtcTicks = DateTime.UtcNow.Ticks },
+                new AlarmHistorianEventDto { EventId = "ev-2", SourceName = "Tank.HiHi", AlarmType = "Acknowledged", Severity = 800, EventTimeUtcTicks = DateTime.UtcNow.Ticks },
+            },
+        };
+
+        var reply = await RoundTripAsync<WriteAlarmEventsRequest, WriteAlarmEventsReply>(
+            MessageKind.WriteAlarmEventsRequest, MessageKind.WriteAlarmEventsReply,
+            request, handler);
+
+        reply.Success.ShouldBeTrue();
+        reply.PerEventOk.Length.ShouldBe(2);
+        reply.PerEventOk[0].ShouldBeTrue();
+        reply.PerEventOk[1].ShouldBeFalse();
+        alarmWriter.Received.Count.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task WriteAlarmEvents_FailsCleanly_WhenNoWriterConfigured()
+    {
+        var historian = new FakeHistorian();
+        var handler = new HistorianFrameHandler(historian, Quiet, alarmWriter: null);
+
+        var reply = await RoundTripAsync<WriteAlarmEventsRequest, WriteAlarmEventsReply>(
+            MessageKind.WriteAlarmEventsRequest, MessageKind.WriteAlarmEventsReply,
+            new WriteAlarmEventsRequest
+            {
+                CorrelationId = "wa-2",
+                Events = new[] { new AlarmHistorianEventDto { EventId = "ev-1" } },
+            }, handler);
+
+        reply.Success.ShouldBeFalse();
+        reply.Error.ShouldNotBeNull();
+        reply.PerEventOk.Length.ShouldBe(1);
+        reply.PerEventOk[0].ShouldBeFalse();
+    }
+
+    [Fact]
+    public async Task FrameReader_FrameWriter_RoundTripPreservesKindAndBody()
+    {
+        // Pure framing-layer test — confirms the length-prefix + kind-byte + body protocol
+        // is the same on both sides without any handler in the loop.
+        using var stream = new MemoryStream();
+        using var writer = new FrameWriter(stream, leaveOpen: true);
+
+        var hello = new Hello { ProtocolMajor = 1, PeerName = "test-peer", SharedSecret = "secret" };
+        await writer.WriteAsync(MessageKind.Hello, hello, CancellationToken.None);
+
+        stream.Position = 0;
+        using var reader = new FrameReader(stream, leaveOpen: true);
+        var frame = await reader.ReadFrameAsync(CancellationToken.None);
+
+        frame.ShouldNotBeNull();
+        frame!.Value.Kind.ShouldBe(MessageKind.Hello);
+        var decoded = MessagePackSerializer.Deserialize<Hello>(frame.Value.Body);
+        decoded.PeerName.ShouldBe("test-peer");
+        decoded.SharedSecret.ShouldBe("secret");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/ProgramSmokeTests.cs

@@ -0,0 +1,21 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests;
+
+/// <summary>
+///     Smoke test confirming the sidecar project links and the test project resolves a
+///     ProjectReference to it. Real behavioural tests arrive in PR 3.2 (backend lift) and
+///     PR 3.3 (pipe server). For PR 3.1 we just verify the assembly identity is what the
+///     csproj declares.
+/// </summary>
+public class ProgramSmokeTests
+{
+    [Fact]
+    public void Program_Assembly_HasExpectedName()
+    {
+        typeof(Program).Assembly.GetName().Name
+            .ShouldBe("OtOpcUa.Driver.Historian.Wonderware");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests.csproj

@@ -0,0 +1,28 @@
+<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.Historian.Wonderware.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.Historian.Wonderware\ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.csproj"/>
+    </ItemGroup>
+
+</Project>

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusCoalescingAutoRecoveryTests.cs

@@ -156,6 +156,38 @@ public sealed class ModbusCoalescingAutoRecoveryTests
         await drv.ShutdownAsync(CancellationToken.None);
     }
 
+    [Fact]
+    public async Task GetAutoProhibitedRanges_Surfaces_Operator_Visible_Snapshot()
+    {
+        // #152 — diagnostic accessor returns the live prohibition map as a snapshot of public
+        // ModbusAutoProhibition records. Consumers (Admin UI, dashboards) project this list
+        // into whatever shape they need.
+        var fake = new ProtectedHoleTransport { ProtectedAddress = 102 };
+        var t100 = new ModbusTagDefinition("T100", ModbusRegion.HoldingRegisters, 100, ModbusDataType.Int16);
+        var t102 = new ModbusTagDefinition("T102", ModbusRegion.HoldingRegisters, 102, ModbusDataType.Int16);
+        var t104 = new ModbusTagDefinition("T104", ModbusRegion.HoldingRegisters, 104, ModbusDataType.Int16);
+        var opts = new ModbusDriverOptions { Host = "f", UnitId = 7, Tags = [t100, t102, t104], MaxReadGap = 5,
+            Probe = new ModbusProbeOptions { Enabled = false } };
+        var drv = new ModbusDriver(opts, "m1", _ => fake);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        // Pre-failure: nothing prohibited.
+        drv.GetAutoProhibitedRanges().ShouldBeEmpty();
+
+        await drv.ReadAsync(["T100", "T102", "T104"], CancellationToken.None);
+
+        var snapshot = drv.GetAutoProhibitedRanges();
+        snapshot.Count.ShouldBe(1);
+        snapshot[0].UnitId.ShouldBe((byte)7);
+        snapshot[0].Region.ShouldBe(ModbusRegion.HoldingRegisters);
+        snapshot[0].StartAddress.ShouldBe((ushort)100);
+        snapshot[0].EndAddress.ShouldBe((ushort)104);
+        snapshot[0].BisectionPending.ShouldBeTrue("multi-register prohibition starts split-pending");
+        snapshot[0].LastProbedUtc.ShouldBeGreaterThan(DateTime.UtcNow.AddMinutes(-1));
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
     [Fact]
     public async Task Tags_Outside_Prohibited_Range_Still_Coalesce()
     {

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusCoalescingBisectionTests.cs

@@ -0,0 +1,171 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests;
+
+/// <summary>
+///     #150 — bisection-style range narrowing for coalescing prohibitions. After a coalesced
+///     read fails, the re-probe loop bisects the prohibited range over multiple ticks until
+///     it pinpoints the actual protected register(s). Healthy halves get cleared as the
+///     bisection narrows.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class ModbusCoalescingBisectionTests
+{
+    /// <summary>
+    ///     Programmable transport like the one in ModbusCoalescingAutoRecoveryTests but local
+    ///     to keep this test file standalone — having the protection model live next to the
+    ///     bisection assertions makes the test intent easier to read.
+    /// </summary>
+    private sealed class ProtectedHoleTransport : IModbusTransport
+    {
+        public ushort ProtectedAddress { get; set; } = ushort.MaxValue;
+        public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
+        public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
+        {
+            var addr = (ushort)((pdu[1] << 8) | pdu[2]);
+            var qty = (ushort)((pdu[3] << 8) | pdu[4]);
+            if (pdu[0] is 0x03 or 0x04 && ProtectedAddress >= addr && ProtectedAddress < addr + qty)
+                return Task.FromException<byte[]>(new ModbusException(pdu[0], 0x02, "IllegalDataAddress"));
+            switch (pdu[0])
+            {
+                case 0x03: case 0x04:
+                {
+                    var resp = new byte[2 + qty * 2];
+                    resp[0] = pdu[0]; resp[1] = (byte)(qty * 2);
+                    return Task.FromResult(resp);
+                }
+                default: return Task.FromResult(new byte[] { pdu[0], 0, 0 });
+            }
+        }
+        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+    }
+
+    [Fact]
+    public async Task Bisection_Narrows_Multi_Register_Prohibition_Per_Reprobe()
+    {
+        var fake = new ProtectedHoleTransport { ProtectedAddress = 105 };
+        // 11 tags 100..110 with MaxReadGap=10 → coalesce into one block 100..110. The protected
+        // register is in the middle (105). After the first failure the planner records the
+        // full 100..110 range as split-pending. Each subsequent re-probe bisects until the
+        // prohibition is pinned at register 105.
+        var tags = Enumerable.Range(100, 11)
+            .Select(i => new ModbusTagDefinition($"T{i}", ModbusRegion.HoldingRegisters, (ushort)i, ModbusDataType.Int16))
+            .ToArray();
+        var opts = new ModbusDriverOptions { Host = "f", Tags = tags, MaxReadGap = 10,
+            AutoProhibitReprobeInterval = TimeSpan.FromMilliseconds(100),
+            Probe = new ModbusProbeOptions { Enabled = false } };
+        var drv = new ModbusDriver(opts, "m1", _ => fake);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(tags.Select(t => t.Name).ToArray(), CancellationToken.None);
+        // Initial prohibition: full 100..110 range, split-pending.
+        drv.AutoProhibitedRangeCount.ShouldBe(1);
+
+        // Re-probe pass 1: bisect 100..110 → mid=105 → left=100..105 (fails because 105 is
+        // protected), right=106..110 (succeeds). Result: prohibition collapses to 100..105.
+        await drv.RunReprobeOnceForTestAsync(CancellationToken.None);
+        drv.AutoProhibitedRangeCount.ShouldBe(1, "after pass 1 the prohibition narrows but doesn't disappear");
+
+        // Re-probe pass 2: bisect 100..105 → mid=102 → left=100..102 (succeeds), right=103..105 (fails).
+        // Result: prohibition collapses to 103..105.
+        await drv.RunReprobeOnceForTestAsync(CancellationToken.None);
+
+        // Re-probe pass 3: bisect 103..105 → mid=104 → left=103..104 (succeeds), right=105..105 (fails).
+        // Result: prohibition collapses to 105..105 (single register, no longer split-pending).
+        await drv.RunReprobeOnceForTestAsync(CancellationToken.None);
+        drv.AutoProhibitedRangeCount.ShouldBe(1, "single-register prohibition stays after bisection terminates");
+
+        // Re-probe pass 4: 105..105 is single-register; straight-retry path. Still fails;
+        // prohibition stays.
+        await drv.RunReprobeOnceForTestAsync(CancellationToken.None);
+        drv.AutoProhibitedRangeCount.ShouldBe(1);
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Bisection_Clears_When_Both_Halves_Are_Healthy()
+    {
+        // Transient failure scenario: range failed once, but by the next re-probe the PLC has
+        // unlocked it. Bisection of (100..110) returns success on both halves → entry removed
+        // entirely.
+        var fake = new ProtectedHoleTransport { ProtectedAddress = 105 };
+        var tags = Enumerable.Range(100, 11)
+            .Select(i => new ModbusTagDefinition($"T{i}", ModbusRegion.HoldingRegisters, (ushort)i, ModbusDataType.Int16))
+            .ToArray();
+        var opts = new ModbusDriverOptions { Host = "f", Tags = tags, MaxReadGap = 10,
+            AutoProhibitReprobeInterval = TimeSpan.FromMilliseconds(100),
+            Probe = new ModbusProbeOptions { Enabled = false } };
+        var drv = new ModbusDriver(opts, "m1", _ => fake);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(tags.Select(t => t.Name).ToArray(), CancellationToken.None);
+        drv.AutoProhibitedRangeCount.ShouldBe(1);
+
+        // Operator unlocks the protected register before the re-probe runs.
+        fake.ProtectedAddress = ushort.MaxValue;
+
+        await drv.RunReprobeOnceForTestAsync(CancellationToken.None);
+        drv.AutoProhibitedRangeCount.ShouldBe(0, "both bisected halves succeed → parent prohibition cleared entirely");
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Bisection_Splits_Into_Two_When_Both_Halves_Still_Fail()
+    {
+        // Two protected registers in the same coalesced range: 102 and 108. After bisection,
+        // both halves of the original (100..110) range still contain a protected address
+        // (left=100..105 contains 102, right=106..110 contains 108). The prohibition replaces
+        // the parent with TWO smaller split-pending entries.
+        var fake = new ProtectedHoleTransport();
+        // Build a more elaborate transport that protects two addresses.
+        var twoHole = new TwoHoleTransport { ProtectedAddresses = { 102, 108 } };
+        var tags = Enumerable.Range(100, 11)
+            .Select(i => new ModbusTagDefinition($"T{i}", ModbusRegion.HoldingRegisters, (ushort)i, ModbusDataType.Int16))
+            .ToArray();
+        var opts = new ModbusDriverOptions { Host = "f", Tags = tags, MaxReadGap = 10,
+            AutoProhibitReprobeInterval = TimeSpan.FromMilliseconds(100),
+            Probe = new ModbusProbeOptions { Enabled = false } };
+        var drv = new ModbusDriver(opts, "m1", _ => twoHole);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(tags.Select(t => t.Name).ToArray(), CancellationToken.None);
+        drv.AutoProhibitedRangeCount.ShouldBe(1);
+
+        // Re-probe: bisect 100..110 at mid=105 → left=100..105 (contains 102, fails),
+        // right=106..110 (contains 108, fails). Result: TWO entries in place of the parent.
+        await drv.RunReprobeOnceForTestAsync(CancellationToken.None);
+        drv.AutoProhibitedRangeCount.ShouldBe(2, "both halves still fail → prohibition splits into two");
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    private sealed class TwoHoleTransport : IModbusTransport
+    {
+        public readonly HashSet<ushort> ProtectedAddresses = new();
+        public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
+        public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
+        {
+            var addr = (ushort)((pdu[1] << 8) | pdu[2]);
+            var qty = (ushort)((pdu[3] << 8) | pdu[4]);
+            if (pdu[0] is 0x03 or 0x04)
+                for (var i = 0; i < qty; i++)
+                    if (ProtectedAddresses.Contains((ushort)(addr + i)))
+                        return Task.FromException<byte[]>(new ModbusException(pdu[0], 0x02, "IllegalDataAddress"));
+            switch (pdu[0])
+            {
+                case 0x03: case 0x04:
+                {
+                    var resp = new byte[2 + qty * 2];
+                    resp[0] = pdu[0]; resp[1] = (byte)(qty * 2);
+                    return Task.FromResult(resp);
+                }
+                default: return Task.FromResult(new byte[] { pdu[0], 0, 0 });
+            }
+        }
+        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLoggerInjectionTests.cs

@@ -0,0 +1,99 @@
+using Microsoft.Extensions.Logging;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests;
+
+/// <summary>
+///     #153 — confirm ModbusDriver emits structured warnings on first-fire of an
+///     auto-prohibition and informational logs on re-probe clearance. The logger plumbing
+///     extends through ModbusDriverFactoryExtensions.Register so production server-bootstrap
+///     paths get the logger automatically; here we exercise the constructor injection
+///     directly.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class ModbusLoggerInjectionTests
+{
+    private sealed class CapturingLogger : ILogger<ModbusDriver>
+    {
+        public readonly List<(LogLevel Level, string Message)> Entries = new();
+        public IDisposable BeginScope<TState>(TState state) where TState : notnull => NullScope.Instance;
+        public bool IsEnabled(LogLevel logLevel) => true;
+        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
+            => Entries.Add((logLevel, formatter(state, exception)));
+        private sealed class NullScope : IDisposable { public static readonly NullScope Instance = new(); public void Dispose() { } }
+    }
+
+    private sealed class ProtectedHoleTransport : IModbusTransport
+    {
+        public ushort ProtectedAddress { get; set; } = 102;
+        public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
+        public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
+        {
+            var addr = (ushort)((pdu[1] << 8) | pdu[2]);
+            var qty = (ushort)((pdu[3] << 8) | pdu[4]);
+            if (pdu[0] is 0x03 && ProtectedAddress >= addr && ProtectedAddress < addr + qty)
+                return Task.FromException<byte[]>(new ModbusException(0x03, 0x02, "IllegalDataAddress"));
+            var resp = new byte[2 + qty * 2];
+            resp[0] = pdu[0]; resp[1] = (byte)(qty * 2);
+            return Task.FromResult(resp);
+        }
+        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+    }
+
+    [Fact]
+    public async Task First_Failure_Emits_Single_Warning_Subsequent_Refire_Stays_Quiet()
+    {
+        var fake = new ProtectedHoleTransport();
+        var logger = new CapturingLogger();
+        var t100 = new ModbusTagDefinition("T100", ModbusRegion.HoldingRegisters, 100, ModbusDataType.Int16);
+        var t102 = new ModbusTagDefinition("T102", ModbusRegion.HoldingRegisters, 102, ModbusDataType.Int16);
+        var t104 = new ModbusTagDefinition("T104", ModbusRegion.HoldingRegisters, 104, ModbusDataType.Int16);
+        var opts = new ModbusDriverOptions { Host = "f", Tags = [t100, t102, t104], MaxReadGap = 5,
+            Probe = new ModbusProbeOptions { Enabled = false } };
+        var drv = new ModbusDriver(opts, "drv-logged", _ => fake, logger: logger);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        // Scan 1 — coalesced read fails. Expect exactly one warning.
+        await drv.ReadAsync(["T100", "T102", "T104"], CancellationToken.None);
+        var warnings = logger.Entries.Where(e => e.Level == LogLevel.Warning).ToList();
+        warnings.Count.ShouldBe(1);
+        warnings[0].Message.ShouldContain("drv-logged");
+        warnings[0].Message.ShouldContain("Start=100");
+        warnings[0].Message.ShouldContain("End=104");
+
+        // Scan 2 — same coalesced range still fails. Re-fire is suppressed (planner sees
+        // the prohibition and skips the merge; even if it didn't, the de-dupe in
+        // RecordAutoProhibition would suppress).
+        await drv.ReadAsync(["T100", "T102", "T104"], CancellationToken.None);
+        logger.Entries.Count(e => e.Level == LogLevel.Warning).ShouldBe(1, "re-fire of same range stays silent");
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Reprobe_Clearing_Prohibition_Emits_Information_Log()
+    {
+        var fake = new ProtectedHoleTransport();
+        var logger = new CapturingLogger();
+        var t100 = new ModbusTagDefinition("T100", ModbusRegion.HoldingRegisters, 100, ModbusDataType.Int16);
+        var t102 = new ModbusTagDefinition("T102", ModbusRegion.HoldingRegisters, 102, ModbusDataType.Int16);
+        var t104 = new ModbusTagDefinition("T104", ModbusRegion.HoldingRegisters, 104, ModbusDataType.Int16);
+        var opts = new ModbusDriverOptions { Host = "f", Tags = [t100, t102, t104], MaxReadGap = 5,
+            AutoProhibitReprobeInterval = TimeSpan.FromHours(1),  // long interval — we drive it manually
+            Probe = new ModbusProbeOptions { Enabled = false } };
+        var drv = new ModbusDriver(opts, "drv-logged", _ => fake, logger: logger);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["T100", "T102", "T104"], CancellationToken.None);
+        // Operator unlocks the protected register; re-probe should clear + log.
+        fake.ProtectedAddress = ushort.MaxValue;
+        await drv.RunReprobeOnceForTestAsync(CancellationToken.None);
+
+        var infoLogs = logger.Entries.Where(e => e.Level == LogLevel.Information && e.Message.Contains("cleared")).ToList();
+        infoLogs.Count.ShouldBeGreaterThanOrEqualTo(1, "re-probe success must emit a 'cleared' info log");
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Server.Tests/Alarms/AlarmConditionServiceTests.cs

@@ -0,0 +1,331 @@
+using System.Collections.Concurrent;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Server.Alarms;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Tests.Alarms;
+
+/// <summary>
+///     Server-level alarm-condition state-machine tests added in PR 2.2. Ports the live
+///     transition cases from <c>GalaxyAlarmTrackerTests</c> against the new
+///     driver-agnostic <see cref="AlarmConditionService"/>: sub-attribute references come
+///     from <see cref="AlarmConditionInfo"/>, value changes flow as
+///     <see cref="DataValueSnapshot"/> instead of MX-specific <c>Vtq</c>, and the ack
+///     write path is decoupled into <see cref="IAlarmAcknowledger"/>.
+/// </summary>
+public sealed class AlarmConditionServiceTests
+{
+    private const string ConditionId = "TankFarm.Tank1.Level.HiHi";
+    private const string InAlarmRef = "TankFarm.Tank1.Level.HiHi.InAlarm";
+    private const string PriorityRef = "TankFarm.Tank1.Level.HiHi.Priority";
+    private const string DescRef = "TankFarm.Tank1.Level.HiHi.DescAttrName";
+    private const string AckedRef = "TankFarm.Tank1.Level.HiHi.Acked";
+    private const string AckMsgWriteRef = "TankFarm.Tank1.Level.HiHi.AckMsg";
+
+    private static AlarmConditionInfo Info(
+        string? inAlarm = InAlarmRef, string? priority = PriorityRef,
+        string? desc = DescRef, string? acked = AckedRef, string? ackMsg = AckMsgWriteRef)
+        => new(
+            SourceName: ConditionId,
+            InitialSeverity: AlarmSeverity.Medium,
+            InitialDescription: null,
+            InAlarmRef: inAlarm,
+            PriorityRef: priority,
+            DescAttrNameRef: desc,
+            AckedRef: acked,
+            AckMsgWriteRef: ackMsg);
+
+    private static DataValueSnapshot Bool(bool v) =>
+        new(v, StatusCode: 0, SourceTimestampUtc: DateTime.UtcNow, ServerTimestampUtc: DateTime.UtcNow);
+    private static DataValueSnapshot Int(int v) =>
+        new(v, 0, DateTime.UtcNow, DateTime.UtcNow);
+    private static DataValueSnapshot Str(string v) =>
+        new(v, 0, DateTime.UtcNow, DateTime.UtcNow);
+
+    private sealed class FakeAcker : IAlarmAcknowledger
+    {
+        public readonly ConcurrentQueue<(string Ref, string Comment)> Writes = new();
+        public bool ReturnValue { get; set; } = true;
+
+        public Task<bool> WriteAckMessageAsync(string ackMsgWriteRef, string comment, CancellationToken cancellationToken)
+        {
+            Writes.Enqueue((ackMsgWriteRef, comment));
+            return Task.FromResult(ReturnValue);
+        }
+    }
+
+    [Fact]
+    public void Track_AddsCondition_AndExposesSubscribedReferences()
+    {
+        using var svc = new AlarmConditionService();
+
+        svc.Track(ConditionId, Info());
+
+        svc.TrackedCount.ShouldBe(1);
+        var refs = svc.GetSubscribedReferences();
+        refs.ShouldContain(InAlarmRef);
+        refs.ShouldContain(PriorityRef);
+        refs.ShouldContain(DescRef);
+        refs.ShouldContain(AckedRef);
+        refs.Count.ShouldBe(4);
+    }
+
+    [Fact]
+    public void Track_IsIdempotentOnRepeatCall()
+    {
+        using var svc = new AlarmConditionService();
+
+        svc.Track(ConditionId, Info());
+        svc.Track(ConditionId, Info());
+
+        svc.TrackedCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public void Track_OmitsNullSubAttributeRefs()
+    {
+        using var svc = new AlarmConditionService();
+
+        // Driver may not expose every sub-attribute (e.g. no .Acked observable).
+        svc.Track(ConditionId, Info(priority: null, desc: null, acked: null));
+
+        svc.GetSubscribedReferences().ShouldBe(new[] { InAlarmRef });
+    }
+
+    [Fact]
+    public void InAlarmFalseToTrue_FiresActiveTransition()
+    {
+        using var svc = new AlarmConditionService();
+        var transitions = new ConcurrentQueue<AlarmConditionTransition>();
+        svc.TransitionRaised += (_, t) => transitions.Enqueue(t);
+        svc.Track(ConditionId, Info());
+
+        svc.OnValueChanged(PriorityRef, Int(500));
+        svc.OnValueChanged(DescRef, Str("Tank level high-high"));
+        svc.OnValueChanged(InAlarmRef, Bool(true));
+
+        transitions.Count.ShouldBe(1);
+        transitions.TryDequeue(out var t).ShouldBeTrue();
+        t!.Transition.ShouldBe(AlarmStateTransition.Active);
+        t.Priority.ShouldBe(500);
+        t.Description.ShouldBe("Tank level high-high");
+        t.ConditionId.ShouldBe(ConditionId);
+    }
+
+    [Fact]
+    public void InAlarmTrueToFalse_FiresInactiveTransition()
+    {
+        using var svc = new AlarmConditionService();
+        var transitions = new ConcurrentQueue<AlarmConditionTransition>();
+        svc.TransitionRaised += (_, t) => transitions.Enqueue(t);
+        svc.Track(ConditionId, Info());
+
+        svc.OnValueChanged(InAlarmRef, Bool(true));
+        svc.OnValueChanged(InAlarmRef, Bool(false));
+
+        transitions.Count.ShouldBe(2);
+        transitions.TryDequeue(out _);
+        transitions.TryDequeue(out var t).ShouldBeTrue();
+        t!.Transition.ShouldBe(AlarmStateTransition.Inactive);
+    }
+
+    [Fact]
+    public void AckedFalseToTrue_FiresAcknowledged_WhileActive()
+    {
+        using var svc = new AlarmConditionService();
+        var transitions = new ConcurrentQueue<AlarmConditionTransition>();
+        svc.TransitionRaised += (_, t) => transitions.Enqueue(t);
+        svc.Track(ConditionId, Info());
+
+        svc.OnValueChanged(InAlarmRef, Bool(true));   // Active, resets Acked → false
+        svc.OnValueChanged(AckedRef, Bool(true));     // Acknowledged
+
+        transitions.Count.ShouldBe(2);
+        transitions.TryDequeue(out _);
+        transitions.TryDequeue(out var t).ShouldBeTrue();
+        t!.Transition.ShouldBe(AlarmStateTransition.Acknowledged);
+    }
+
+    [Fact]
+    public void AckedTransitionWhileInactive_DoesNotFire()
+    {
+        using var svc = new AlarmConditionService();
+        var transitions = new ConcurrentQueue<AlarmConditionTransition>();
+        svc.TransitionRaised += (_, t) => transitions.Enqueue(t);
+        svc.Track(ConditionId, Info());
+
+        // Initial Acked=true on subscribe (alarm at rest, pre-ack'd) — must not fire.
+        svc.OnValueChanged(AckedRef, Bool(true));
+
+        transitions.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void RepeatedActiveTransitions_ResetAckedFlag()
+    {
+        using var svc = new AlarmConditionService();
+        var transitions = new ConcurrentQueue<AlarmConditionTransition>();
+        svc.TransitionRaised += (_, t) => transitions.Enqueue(t);
+        svc.Track(ConditionId, Info());
+
+        // Cycle 1: active → ack → inactive → active again
+        svc.OnValueChanged(InAlarmRef, Bool(true));
+        svc.OnValueChanged(AckedRef, Bool(true));
+        svc.OnValueChanged(InAlarmRef, Bool(false));
+        svc.OnValueChanged(InAlarmRef, Bool(true));   // re-arms — Acked must reset to false
+        svc.OnValueChanged(AckedRef, Bool(true));     // produces a fresh Acknowledged
+
+        // Active, Acknowledged, Inactive, Active, Acknowledged
+        transitions.Count.ShouldBe(5);
+        var ordered = transitions.Select(t => t.Transition).ToArray();
+        ordered.ShouldBe(new[]
+        {
+            AlarmStateTransition.Active,
+            AlarmStateTransition.Acknowledged,
+            AlarmStateTransition.Inactive,
+            AlarmStateTransition.Active,
+            AlarmStateTransition.Acknowledged,
+        });
+    }
+
+    [Fact]
+    public async Task AcknowledgeAsync_RoutesToAckerWithAckMsgRef()
+    {
+        using var svc = new AlarmConditionService();
+        var acker = new FakeAcker();
+        svc.Track(ConditionId, Info(), acker);
+
+        var ok = await svc.AcknowledgeAsync(ConditionId, "operator-1: cleared", CancellationToken.None);
+
+        ok.ShouldBeTrue();
+        acker.Writes.Count.ShouldBe(1);
+        acker.Writes.TryDequeue(out var w).ShouldBeTrue();
+        w.Ref.ShouldBe(AckMsgWriteRef);
+        w.Comment.ShouldBe("operator-1: cleared");
+    }
+
+    [Fact]
+    public async Task AcknowledgeAsync_ReturnsFalse_WhenConditionUntracked()
+    {
+        using var svc = new AlarmConditionService();
+        var acker = new FakeAcker();
+        svc.Track("OtherCondition", Info(), acker);
+
+        var ok = await svc.AcknowledgeAsync(ConditionId, "comment");
+
+        ok.ShouldBeFalse();
+        acker.Writes.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public async Task AcknowledgeAsync_ReturnsFalse_WhenNoAckerRegistered()
+    {
+        using var svc = new AlarmConditionService();
+        svc.Track(ConditionId, Info(), acker: null);
+
+        var ok = await svc.AcknowledgeAsync(ConditionId, "comment");
+
+        ok.ShouldBeFalse();
+    }
+
+    [Fact]
+    public async Task AcknowledgeAsync_ReturnsFalse_WhenAckMsgRefMissing()
+    {
+        using var svc = new AlarmConditionService();
+        var acker = new FakeAcker();
+        svc.Track(ConditionId, Info(ackMsg: null), acker);
+
+        var ok = await svc.AcknowledgeAsync(ConditionId, "comment");
+
+        ok.ShouldBeFalse();
+        acker.Writes.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Snapshot_ReportsLatestFields()
+    {
+        using var svc = new AlarmConditionService();
+        svc.Track(ConditionId, Info());
+        svc.OnValueChanged(InAlarmRef, Bool(true));
+        svc.OnValueChanged(PriorityRef, Int(900));
+        svc.OnValueChanged(DescRef, Str("MyAlarm"));
+        svc.OnValueChanged(AckedRef, Bool(true));
+
+        var snap = svc.Snapshot();
+
+        snap.Count.ShouldBe(1);
+        snap[0].ConditionId.ShouldBe(ConditionId);
+        snap[0].InAlarm.ShouldBeTrue();
+        snap[0].Acked.ShouldBeTrue();
+        snap[0].Priority.ShouldBe(900);
+        snap[0].Description.ShouldBe("MyAlarm");
+    }
+
+    [Fact]
+    public void OnValueChanged_ForUnknownReference_IsSilentlyIgnored()
+    {
+        using var svc = new AlarmConditionService();
+        var transitions = new ConcurrentQueue<AlarmConditionTransition>();
+        svc.TransitionRaised += (_, t) => transitions.Enqueue(t);
+
+        svc.OnValueChanged("Some.Random.Tag.InAlarm", Bool(true));
+
+        transitions.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Untrack_RemovesConditionAndReleasesReferences()
+    {
+        using var svc = new AlarmConditionService();
+        svc.Track(ConditionId, Info());
+
+        svc.Untrack(ConditionId);
+
+        svc.TrackedCount.ShouldBe(0);
+        svc.GetSubscribedReferences().ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Untrack_NonexistentConditionIsNoOp()
+    {
+        using var svc = new AlarmConditionService();
+        svc.Track(ConditionId, Info());
+
+        Should.NotThrow(() => svc.Untrack("does-not-exist"));
+        svc.TrackedCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public void Track_ThrowsAfterDisposal()
+    {
+        var svc = new AlarmConditionService();
+        svc.Dispose();
+
+        Should.Throw<ObjectDisposedException>(() => svc.Track(ConditionId, Info()));
+    }
+
+    [Fact]
+    public void OnValueChanged_AfterDisposal_IsSilentlyDropped()
+    {
+        var svc = new AlarmConditionService();
+        svc.Track(ConditionId, Info());
+        svc.Dispose();
+
+        // Stale callbacks during disposal must not throw.
+        Should.NotThrow(() => svc.OnValueChanged(InAlarmRef, Bool(true)));
+    }
+
+    [Fact]
+    public void PriorityCoercion_AcceptsCommonNumericTypes()
+    {
+        using var svc = new AlarmConditionService();
+        svc.Track(ConditionId, Info());
+
+        svc.OnValueChanged(PriorityRef, new DataValueSnapshot((short)123, 0, null, DateTime.UtcNow));
+        svc.OnValueChanged(InAlarmRef, Bool(true));
+
+        var snap = svc.Snapshot()[0];
+        snap.Priority.ShouldBe(123);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Server.Tests/HealthEndpointsHostTests.cs

@@ -157,6 +157,76 @@ public sealed class HealthEndpointsHostTests : IAsyncLifetime
         response.StatusCode.ShouldBe(System.Net.HttpStatusCode.NotFound);
     }
 
+    // ===== #154 — driver-diagnostics endpoint =====
+
+    [Fact]
+    public async Task Diagnostics_ReturnsModbusAutoProhibitions_ForLiveDriver()
+    {
+        // Bring up a Modbus driver with a programmable transport that protects register 102,
+        // record one prohibition, then hit /diagnostics/drivers/{id}/modbus/auto-prohibited.
+        var fake = new ModbusDriverDiagnosticsTransport { ProtectedAddress = 102 };
+        var t1 = new ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusTagDefinition(
+            "T1", ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusRegion.HoldingRegisters, 100, ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusDataType.Int16);
+        var t2 = new ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusTagDefinition(
+            "T2", ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusRegion.HoldingRegisters, 102, ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusDataType.Int16);
+        var opts = new ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusDriverOptions
+        {
+            Host = "f", Tags = [t1, t2], MaxReadGap = 5,
+            Probe = new ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusProbeOptions { Enabled = false },
+        };
+        var driver = new ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusDriver(opts, "diag-mb", _ => fake);
+        await _driverHost.RegisterAsync(driver, "{}", CancellationToken.None);
+        await driver.ReadAsync(["T1", "T2"], CancellationToken.None);
+
+        Start();
+
+        var response = await _client.GetAsync("/diagnostics/drivers/diag-mb/modbus/auto-prohibited");
+
+        response.IsSuccessStatusCode.ShouldBeTrue();
+        var body = JsonDocument.Parse(await response.Content.ReadAsStringAsync()).RootElement;
+        body.GetProperty("driverInstanceId").GetString().ShouldBe("diag-mb");
+        body.GetProperty("count").GetInt32().ShouldBe(1);
+        var first = body.GetProperty("ranges")[0];
+        first.GetProperty("startAddress").GetInt32().ShouldBe(100);
+        first.GetProperty("endAddress").GetInt32().ShouldBe(102);
+        first.GetProperty("region").GetString().ShouldBe("HoldingRegisters");
+        first.GetProperty("bisectionPending").GetBoolean().ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task Diagnostics_404_When_Driver_Not_Found()
+    {
+        Start();
+        var response = await _client.GetAsync("/diagnostics/drivers/no-such/modbus/auto-prohibited");
+        response.StatusCode.ShouldBe(System.Net.HttpStatusCode.NotFound);
+    }
+
+    [Fact]
+    public async Task Diagnostics_400_When_Driver_Is_Wrong_Type()
+    {
+        await _driverHost.RegisterAsync(new StubDriver("not-modbus", DriverState.Healthy), "{}", CancellationToken.None);
+        Start();
+        var response = await _client.GetAsync("/diagnostics/drivers/not-modbus/modbus/auto-prohibited");
+        response.StatusCode.ShouldBe(System.Net.HttpStatusCode.BadRequest);
+    }
+
+    private sealed class ModbusDriverDiagnosticsTransport : ZB.MOM.WW.OtOpcUa.Driver.Modbus.IModbusTransport
+    {
+        public ushort ProtectedAddress { get; set; } = 102;
+        public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
+        public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
+        {
+            var addr = (ushort)((pdu[1] << 8) | pdu[2]);
+            var qty = (ushort)((pdu[3] << 8) | pdu[4]);
+            if (pdu[0] is 0x03 && ProtectedAddress >= addr && ProtectedAddress < addr + qty)
+                return Task.FromException<byte[]>(new ZB.MOM.WW.OtOpcUa.Driver.Modbus.ModbusException(0x03, 0x02, "IllegalDataAddress"));
+            var resp = new byte[2 + qty * 2];
+            resp[0] = pdu[0]; resp[1] = (byte)(qty * 2);
+            return Task.FromResult(resp);
+        }
+        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+    }
+
     private sealed class StubDriver : IDriver
     {
         private readonly DriverState _state;

tests/ZB.MOM.WW.OtOpcUa.Server.Tests/History/HistoryRouterTests.cs

@@ -0,0 +1,169 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Server.History;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Tests.History;
+
+/// <summary>
+///     Tests for <see cref="HistoryRouter"/> registration + resolution semantics added
+///     in PR 1.2. The router is the only seam between OPC UA HistoryRead service calls
+///     and registered <see cref="IHistorianDataSource"/> implementations, so the
+///     resolution rules (case-insensitive prefix, longest-match wins, no source =>
+///     null) need explicit coverage.
+/// </summary>
+public sealed class HistoryRouterTests
+{
+    [Fact]
+    public void Resolve_ReturnsNull_WhenNoSourceRegistered()
+    {
+        using var router = new HistoryRouter();
+        router.Resolve("anything").ShouldBeNull();
+    }
+
+    [Fact]
+    public void Resolve_ReturnsRegisteredSource_WhenPrefixMatches()
+    {
+        using var router = new HistoryRouter();
+        var source = new FakeSource("galaxy");
+        router.Register("galaxy", source);
+
+        router.Resolve("galaxy.TankFarm.Tank1.Level").ShouldBe(source);
+    }
+
+    [Fact]
+    public void Resolve_ReturnsNull_WhenPrefixDoesNotMatch()
+    {
+        using var router = new HistoryRouter();
+        router.Register("galaxy", new FakeSource("galaxy"));
+
+        router.Resolve("modbus.MyDevice.Tag1").ShouldBeNull();
+    }
+
+    [Fact]
+    public void Resolve_LongestPrefixWins_WhenMultipleRegistered()
+    {
+        using var router = new HistoryRouter();
+        var generic = new FakeSource("generic");
+        var specific = new FakeSource("specific");
+
+        router.Register("galaxy", generic);
+        router.Register("galaxy.HighRate", specific);
+
+        router.Resolve("galaxy.HighRate.Sensor1").ShouldBe(specific);
+        router.Resolve("galaxy.LowRate.Sensor2").ShouldBe(generic);
+    }
+
+    [Fact]
+    public void Resolve_IsCaseInsensitive_OnPrefixMatch()
+    {
+        using var router = new HistoryRouter();
+        var source = new FakeSource("galaxy");
+        router.Register("Galaxy", source);
+
+        router.Resolve("galaxy.foo").ShouldBe(source);
+        router.Resolve("GALAXY.foo").ShouldBe(source);
+    }
+
+    [Fact]
+    public void Register_Throws_WhenPrefixAlreadyRegistered()
+    {
+        using var router = new HistoryRouter();
+        router.Register("galaxy", new FakeSource("first"));
+
+        Should.Throw<InvalidOperationException>(
+            () => router.Register("galaxy", new FakeSource("second")));
+    }
+
+    [Fact]
+    public void Dispose_DisposesAllRegisteredSources()
+    {
+        var router = new HistoryRouter();
+        var a = new FakeSource("a");
+        var b = new FakeSource("b");
+        router.Register("ns_a", a);
+        router.Register("ns_b", b);
+
+        router.Dispose();
+
+        a.IsDisposed.ShouldBeTrue();
+        b.IsDisposed.ShouldBeTrue();
+    }
+
+    [Fact]
+    public void Dispose_SwallowsExceptionsFromMisbehavingSource()
+    {
+        var router = new HistoryRouter();
+        var throwing = new ThrowingFakeSource();
+        var clean = new FakeSource("clean");
+        router.Register("bad", throwing);
+        router.Register("good", clean);
+
+        // Even when one source's Dispose throws, the router must finish disposing the
+        // remaining sources (server shutdown invariant).
+        Should.NotThrow(() => router.Dispose());
+        clean.IsDisposed.ShouldBeTrue();
+    }
+
+    [Fact]
+    public void Resolve_Throws_AfterDisposal()
+    {
+        var router = new HistoryRouter();
+        router.Dispose();
+
+        Should.Throw<ObjectDisposedException>(() => router.Resolve("anything"));
+    }
+
+    [Fact]
+    public void Register_Throws_AfterDisposal()
+    {
+        var router = new HistoryRouter();
+        router.Dispose();
+
+        Should.Throw<ObjectDisposedException>(
+            () => router.Register("ns", new FakeSource("x")));
+    }
+
+    private sealed class FakeSource(string name) : IHistorianDataSource
+    {
+        public string Name { get; } = name;
+        public bool IsDisposed { get; private set; }
+
+        public void Dispose() => IsDisposed = true;
+
+        public Task<HistoryReadResult> ReadRawAsync(string fullReference, DateTime startUtc, DateTime endUtc, uint maxValuesPerNode, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public Task<HistoryReadResult> ReadProcessedAsync(string fullReference, DateTime startUtc, DateTime endUtc, TimeSpan interval, HistoryAggregateType aggregate, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public Task<HistoryReadResult> ReadAtTimeAsync(string fullReference, IReadOnlyList<DateTime> timestampsUtc, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public Task<HistoricalEventsResult> ReadEventsAsync(string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public HistorianHealthSnapshot GetHealthSnapshot()
+            => new(0, 0, 0, 0, null, null, null, false, false, null, null, []);
+    }
+
+    private sealed class ThrowingFakeSource : IHistorianDataSource
+    {
+        public void Dispose() => throw new InvalidOperationException("boom");
+
+        public Task<HistoryReadResult> ReadRawAsync(string fullReference, DateTime startUtc, DateTime endUtc, uint maxValuesPerNode, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public Task<HistoryReadResult> ReadProcessedAsync(string fullReference, DateTime startUtc, DateTime endUtc, TimeSpan interval, HistoryAggregateType aggregate, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public Task<HistoryReadResult> ReadAtTimeAsync(string fullReference, IReadOnlyList<DateTime> timestampsUtc, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public Task<HistoricalEventsResult> ReadEventsAsync(string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+
+        public HistorianHealthSnapshot GetHealthSnapshot()
+            => new(0, 0, 0, 0, null, null, null, false, false, null, null, []);
+    }
+}