FOCAS — retire Tier-C split, inline managed wire client, make read-only

Migration closes the FOCAS Tier-C architecture. OtOpcUa previously had
`Driver.FOCAS.Host` (NSSM-wrapped Windows service loading Fwlib64.dll via
P/Invoke) + `Driver.FOCAS.Shared` (MessagePack IPC contracts) + a C shim
DLL stand-in for unit tests. All of it is deleted; the driver is now a
single in-process managed assembly talking the FOCAS/2 Ethernet binary
protocol directly on TCP:8193.

Architecture

- Pure-managed `FocasWireClient` inlined at `src/.../Driver.FOCAS/Wire/`
  (owner-imported — see Wire/FocasWireClient.cs for the full surface).
  Opens two TCP sockets, runs the initiate handshake, serialises requests
  on socket 2 through a semaphore, closes cleanly with PDU + socket
  teardown. Both sync `IDisposable` and async `IAsyncDisposable`.
- `WireFocasClient` (same folder) adapts the wire client to OtOpcUa's
  `IFocasClient` surface — fixed-tree reads, PARAM/MACRO/PMC addresses,
  alarms. Writes return `BadNotWritable` by design — OtOpcUa is read-only
  against FOCAS.
- `FocasDriverFactoryExtensions` now accepts `"Backend": "wire"` (default)
  and `"Backend": "unimplemented"`. Legacy `ipc` and `fwlib` backends are
  rejected at startup with a diagnostic pointing at the migration doc.

Deletions

- `src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Host/` — whole project + Ipc/,
  Backend/, Stability/, Program.cs.
- `src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/` — Contracts/, FrameReader,
  FrameWriter, whole project.
- `tests/...Driver.FOCAS.Host.Tests/` + `.Shared.Tests/` — whole projects.
- `src/.../Driver.FOCAS/FwlibNative.cs` + `FwlibFocasClient.cs` — 21
  P/Invokes + 7 `Pack=1` marshalling structs + the Fwlib-backed
  `IFocasClient` implementation.
- `src/.../Driver.FOCAS/Ipc/` + `Supervisor/` — IPC client wrapper +
  Host-process supervisor (backoff, circuit breaker, heartbeat, post-
  mortem reader, process launcher).
- `scripts/install/Install-FocasHost.ps1` — NSSM service installer.
- `tests/.../Driver.FOCAS.Tests/{IpcFocasClientTests, IpcLoopback,
  FwlibNativeHelperTests, PostMortemReaderCompatibilityTests,
  SupervisorTests, FocasDriverFactoryExtensionsTests}.cs` — tests that
  exercised the retired surfaces.
- `tests/.../Driver.FOCAS.IntegrationTests/Shim/` — the zig-built C shim
  DLL that masqueraded as Fwlib64.dll.

Solution changes

- `ZB.MOM.WW.OtOpcUa.slnx` drops the 4 retired project refs.
- `src/.../Driver.FOCAS.csproj` drops the Shared ProjectReference, adds
  `Microsoft.Extensions.Logging.Abstractions` for the optional `ILogger`
  hook in `FocasWireClient`.
- `src/.../Driver.FOCAS.Cli.csproj` drops the six `<Content Include>`
  entries that copied `vendor/fanuc/*.dll` into the CLI bin. CLI now uses
  `WireFocasClient` directly.
- `FocasDriver` default factory flips to `Wire.WireFocasClientFactory`.

Integration tests

- New `tests/.../Driver.FOCAS.IntegrationTests/` project covering fixed-
  tree reads (identity, axes, dynamic, program, operation mode, timers,
  spindle load + max RPM, servo meters), user-authored PARAM / MACRO /
  PMC reads, `DiscoverAsync` emission, `SubscribeAsync` + `OnDataChange`,
  `IAlarmSource` raise/clear transitions, and `ProbeAsync` /
  `OnHostStatusChanged`. 9 e2e tests against the focas-mock fixture
  (Docker container with the vendored Python mock's native FOCAS/2
  Ethernet responder).
- `scripts/integration/run-focas.ps1` orchestrates compose up → tests →
  compose down. Dropped the shim-build stage + DLL-copy step + the split
  testhost workaround (the latter only existed because of native-DLL
  lifecycle bugs the shim tripped).
- Docker compose collapses from 11 per-series services to one `focas-sim`
  service. Tests seed per-series state via `mock_load_profile` at test
  start.
- Vendored focas-mock snapshot refreshed to pick up upstream's native
  FOCAS/2 Ethernet responder (was 660 lines, now 1018) — the
  pre-refresh snapshot only spoke the JSON admin protocol.

Tests

- 145/145 unit tests in `Driver.FOCAS.Tests` pass (was 208 pre-deletion;
  63 removed tests exercised the retired IPC/shim/supervisor/Fwlib
  surfaces).
- 9/9 integration tests pass against the refreshed mock.
- `FocasScaffoldingTests.Unimplemented_factory_throws_on_Create…` updated
  to assert the new diagnostic message pointing at
  `docs/drivers/FOCAS.md` rather than the now-gone `Fwlib64.dll`.

Docs

- `docs/drivers/FOCAS.md` rewritten for the managed wire topology —
  deployment collapses to one `"Backend": "wire"` config block, no
  separate service, no DLL deployment, no pipe ACL.
- `docs/drivers/FOCAS-Test-Fixture.md` updated — single TCP probe skip
  gate instead of TCP + shim probe; fewer moving parts.
- `docs/drivers/README.md` row for FOCAS reflects the Tier-A managed
  topology (previously listed Tier-C + `Fwlib64.dll` P/Invoke).
- `docs/Driver.FOCAS.Cli.md` drops the Tier-C architecture-note section.
- `docs/v2/implementation/focas-isolation-plan.md` marked historical —
  the plan it documents was executed then superseded by the wire client.
- `docs/v2/v2-release-readiness.md` re-audited 2026-04-24. Phase 5
  driver complement closed. FOCAS change-log entry added.

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

docs/drivers/README.md

@@ -26,7 +26,7 @@ Driver type metadata is registered at startup in `DriverTypeRegistry` (`src/ZB.M
 | AB CIP | `Driver.AbCip` | A | libplctag CIP | IDriver, ITagDiscovery, IReadable, IWritable, ISubscribable, IHostConnectivityProbe, IPerCallHostResolver, IAlarmSource | ControlLogix / CompactLogix. Tag discovery uses the `@tags` walker to enumerate controller-scoped + program-scoped symbols; UDT member resolution via the UDT template reader |
 | AB Legacy | `Driver.AbLegacy` | A | libplctag PCCC | IDriver, ITagDiscovery, IReadable, IWritable, ISubscribable, IHostConnectivityProbe, IPerCallHostResolver | SLC 500 / MicroLogix. File-based addressing (`N7:0`, `F8:0`) — no symbol table, tag list is user-authored in the config DB |
 | TwinCAT | `Driver.TwinCAT` | B | Beckhoff `TwinCAT.Ads` (`TcAdsClient`) | IDriver, ITagDiscovery, IReadable, IWritable, ISubscribable, IHostConnectivityProbe, IPerCallHostResolver | The only native-notification driver outside Galaxy — ADS delivers `ValueChangedCallback` events the driver forwards straight to `ISubscribable.OnDataChange` without polling. Symbol tree uploaded via `SymbolLoaderFactory` |
-| FOCAS | `Driver.FOCAS` | C | FANUC FOCAS2 (`Fwlib32.dll` P/Invoke) | IDriver, ITagDiscovery, IReadable, IWritable, ISubscribable, IHostConnectivityProbe, IPerCallHostResolver | Tier C — FOCAS DLL has crash modes that warrant process isolation. CNC-shaped data model (axes, spindle, PMC, macros, alarms) not a flat tag map |
+| [FOCAS](FOCAS.md) | `Driver.FOCAS` | A | Pure-managed `FocasWireClient` — FOCAS/2 Ethernet binary protocol on TCP:8193, inlined into the driver assembly | IDriver, ITagDiscovery, IReadable, ISubscribable, IHostConnectivityProbe, IPerCallHostResolver, IAlarmSource | Read-only by design (WriteAsync returns `BadNotWritable`). CNC-shaped data model (axes, spindle, PMC, macros, alarms) not a flat tag map. Previously Tier-C (Host + P/Invoke + shim DLL); retired in the 2026-04-24 migration when the managed wire client landed |
 | OPC UA Client | `Driver.OpcUaClient` | B | OPCFoundation `Opc.Ua.Client` | IDriver, ITagDiscovery, IReadable, IWritable, ISubscribable, IAlarmSource, IHistoryProvider, IHostConnectivityProbe | Gateway/aggregation driver. Opens a single `Session` against a remote OPC UA server and re-exposes its address space. Owns its own `ApplicationConfiguration` (distinct from `Client.Shared`) because it's always-on with keep-alive + `TransferSubscriptions` across SDK reconnect, not an interactive CLI |
 
 ## Per-driver documentation
@@ -35,6 +35,9 @@ Driver type metadata is registered at startup in `DriverTypeRegistry` (`src/ZB.M
   - [Galaxy.md](Galaxy.md) — COM bridge, STA pump, IPC, runtime probes
   - [Galaxy-Repository.md](Galaxy-Repository.md) — ZB SQL reader, `LocalPlatform` scope filter, change detection
 
+- **FOCAS** has a short getting-started doc because the Tier-C two-project deployment + backend-selection env var + alarm projection opt-in all need explaining up front:
+  - [FOCAS.md](FOCAS.md) — deployment, config, capability surface, alarm projection, troubleshooting
+
 - **All other drivers** share a single per-driver specification in [docs/v2/driver-specs.md](../v2/driver-specs.md) — addressing, data-type maps, connection settings, and quirks live there. That file is the authoritative per-driver reference; this index points at it rather than duplicating.
 
 ## Test-fixture coverage maps