Phase 2 Streams A+B+C feature-complete — real Win32 pump, all 9 IDriver capabilities, end-to-end IPC dispatch. Streams D+E remain (Galaxy MXAccess code lift + parity-debug cycle, plan-budgeted 3-4 weeks). The 494 v1 IntegrationTests still pass — legacy OtOpcUa.Host untouched. StaPump replaces the BlockingCollection placeholder with a real Win32 message pump lifted from v1 StaComThread per CLAUDE.md "Reference Implementation": dedicated STA Thread with SetApartmentState(STA), GetMessage/PostThreadMessage/PeekMessage/TranslateMessage/DispatchMessage/PostQuitMessage P/Invoke, WM_APP=0x8000 for work-item dispatch, WM_APP+1 for graceful-drain → PostQuitMessage, peek-pm-noremove on entry to force the system to create the thread message queue before signalling Started, IsResponsiveAsync probe still no-op-round-trips through PostThreadMessage so the wedge detection works against the real pump. Concurrent ConcurrentQueue<WorkItem> drains on every WM_APP; fault path on dispose drains-and-faults all pending work-item TCSes with InvalidOperationException("STA pump has exited"). All three StaPumpTests pass against the real pump (apartment state STA, healthy probe true, wedged probe false). GalaxyProxyDriver now implements every Phase 2 Stream C capability — IDriver, ITagDiscovery, IReadable, IWritable, ISubscribable, IAlarmSource, IHistoryProvider, IRediscoverable, IHostConnectivityProbe — each forwarding through the matching IPC contract. ReadAsync preserves request order even when the Host returns out-of-order values; WriteAsync MessagePack-serializes the value into ValueBytes; SubscribeAsync wraps SubscriptionId in a GalaxySubscriptionHandle record; UnsubscribeAsync uses the new SendOneWayAsync helper on GalaxyIpcClient (fire-and-forget but still gated through the call-semaphore so it doesn't interleave with CallAsync); AlarmSubscribe is one-way and the Host pushes events back via OnAlarmEvent; ReadProcessedAsync short-circuits to NotSupportedException (Galaxy historian only does raw); IRediscoverable's OnRediscoveryNeeded fires when the Host pushes a deploy-watermark notification; IHostConnectivityProbe.GetHostStatuses() snapshots and OnHostStatusChanged fires on Running↔Stopped/Faulted transitions, with IpcHostConnectivityStatus aliased to disambiguate from the Core.Abstractions namespace's same-named type. Internal RaiseDataChange/RaiseAlarmEvent/RaiseRediscoveryNeeded/OnHostConnectivityUpdate methods are the entry points the IPC client will invoke when push frames arrive. Host side: new Backend/IGalaxyBackend interface defines the seam between IPC dispatch and the live MXAccess code (so the dispatcher is unit-testable against an in-memory mock without needing live Galaxy); Backend/StubGalaxyBackend returns success for OpenSession/CloseSession/Subscribe/Unsubscribe/AlarmSubscribe/AlarmAck/Recycle and a recognizable "stub: MXAccess code lift pending (Phase 2 Task B.1)"-tagged error for Discover/ReadValues/WriteValues/HistoryRead — keeps the IPC end-to-end testable today and gives the parity team a clear seam to slot the real implementation into; Ipc/GalaxyFrameHandler is the new real dispatcher (replaces StubFrameHandler in Program.cs) — switch on MessageKind, deserialize the matching contract, await backend method, write the response (one-way for Unsubscribe/AlarmSubscribe/AlarmAck/CloseSession), heartbeat handled inline so liveness still works if the backend is sick, exceptions caught and surfaced as ErrorResponse with code "handler-exception" so the Proxy raises GalaxyIpcException instead of disconnecting. End-to-end IPC integration test (EndToEndIpcTests) drives every operation through the full stack — Initialize → Read → Write → Subscribe → Unsubscribe → SubscribeAlarms → AlarmAck → ReadRaw → ReadProcessed (short-circuit) — proving the wire protocol, dispatcher, capability forwarding, and one-way semantics agree end-to-end. Skipped on Windows administrator shells per the same PipeAcl-denies-Administrators reasoning the IpcHandshakeIntegrationTests use. Full solution 952 pass / 1 pre-existing Phase 0 baseline. Phase 2 evidence doc updated: status header now reads "Streams A+B+C complete... Streams D+E remain — gated only on the iterative Galaxy code lift + parity-debug cycle"; new Update 2026-04-17 (later) callout enumerates the upgrade with explicit "what's left for the Phase 2 exit gate" — replace StubGalaxyBackend with a MxAccessClient-backed implementation calling on the StaPump, then run the v1 IntegrationTests against the v2 topology and iterate on parity defects until green, then delete legacy OtOpcUa.Host.

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

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

@@ -38,7 +38,10 @@ public static class Program
 
             Log.Information("OtOpcUaGalaxyHost starting — pipe={Pipe} allowedSid={Sid}", pipeName, allowedSidValue);
 
-            var handler = new StubFrameHandler();
+            // Real frame dispatcher backed by StubGalaxyBackend until the MXAccess code lift
+            // (Phase 2 Task B.1) replaces the backend with the live MxAccessClient-backed one.
+            var backend = new Backend.StubGalaxyBackend();
+            var handler = new GalaxyFrameHandler(backend, Log.Logger);
             server.RunAsync(handler, cts.Token).GetAwaiter().GetResult();
 
             Log.Information("OtOpcUaGalaxyHost stopped cleanly");