task-galaxy-e2e branch — non-FOCAS work-in-progress snapshot

Catch-all commit for pending work on the task-galaxy-e2e branch that
wasn't part of the FOCAS migration. Grouping by topic so future per-topic
commits can be cherry-picked if needed.

TwinCAT
- src/.../Driver.TwinCAT/AdsTwinCATClient.cs + TwinCATDriverFactoryExtensions.cs:
  factory-registration extensions + ADS client refinements.
- src/.../Driver.TwinCAT.Cli/Commands/BrowseCommand.cs: new browse command
  for the TwinCAT test-client CLI.
- tests/.../Driver.TwinCAT.IntegrationTests/TwinCAT3SmokeTests.cs + TwinCatProject/:
  fixture scaffold with a minimal POU + README pointing at the TCBSD/ESXi
  VM for e2e.
- docs/Driver.TwinCAT.Cli.md + docs/drivers/TwinCAT-Test-Fixture.md:
  documentation for the above.
- docs/v3/twincat-backlog.md: forward-looking backlog seed.

Admin UI + fleet status
- src/.../Admin/Components/Pages/Clusters/DriversTab.razor + Hosts.razor:
  UI refresh for fleet-status rendering.
- src/.../Admin/Hubs/FleetStatusHub.cs + FleetStatusPoller.cs +
  Admin/Program.cs: SignalR hub + poller plumbing for live fleet data.
- tests/.../Admin.Tests/FleetStatusPollerTests.cs: poller coverage.

Server + redundancy runtime (Phase 6.3 follow-ups)
- src/.../Server/Hosting/RedundancyPublisherHostedService.cs: HostedService
  that owns the RedundancyStatePublisher lifecycle + wires peer reachability.
- src/.../Server/Redundancy/ServerRedundancyNodeWriter.cs: OPC UA
  variable-node writer binding ServiceLevel + ServerUriArray to the
  publisher's events.
- src/.../Server/Program.cs + Server.csproj: hosted-service registration.
- tests/.../Server.Tests/ServerRedundancyNodeWriterTests.cs +
  Server.Tests.csproj: coverage for the above.

Configuration
- src/.../Configuration/Validation/DraftValidator.cs +
  tests/.../Configuration.Tests/DraftValidatorTests.cs: draft-validation
  refinements.

E2E scripts (shared infrastructure)
- scripts/e2e/README.md + _common.ps1 + test-all.ps1: shared helpers + the
  all-drivers test-all runner.
- scripts/e2e/test-opcuaclient.ps1: OPC UA Client e2e runner.

Docs
- docs/v2/implementation/phase-6-{1,2,3,4}*.md + exit-gate-phase-{3,7}.md:
  phase-gate + implementation doc updates.
- docs/v2/plan.md: top-level plan refresh.
- docs/v2/redundancy-interop-playbook.md: client interop playbook for the
  Phase 6.3 redundancy-runtime work.

Two orphan FOCAS docs remain on disk but deliberately unstaged —
docs/v2/focas-deployment.md and docs/v2/implementation/focas-simulator-plan.md
describe the now-retired Tier-C topology and should either be rewritten
or deleted in a follow-up.

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

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

@@ -153,4 +153,62 @@ END";
             m.Args[0] is AlertMessage alert && alert.NodeId == "p-2-a" && alert.Severity == "error");
         alertMatch.ShouldNotBeNull("poller should have raised AlertRaised for p-2-a");
     }
+
+    [Fact]
+    public async Task Poller_pushes_ResilienceStatusChanged_on_delta()
+    {
+        // Phase 6.1 Stream E.2 — DriverInstanceResilienceStatus row changes should surface
+        // on the fleet hub so /hosts updates without waiting for the 10s poll.
+        using (var scope = _sp.CreateScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<OtOpcUaConfigDbContext>();
+            db.DriverInstanceResilienceStatuses.Add(new DriverInstanceResilienceStatus
+            {
+                DriverInstanceId = "drv-1", HostName = "plc.example.com",
+                ConsecutiveFailures = 2, CurrentBulkheadDepth = 1,
+                LastSampledUtc = DateTime.UtcNow,
+            });
+            await db.SaveChangesAsync();
+        }
+
+        var recorder = new RecordingHubClients();
+        var fleetHub = new RecordingHubContext<FleetStatusHub>(recorder);
+        var alertHub = new RecordingHubContext<AlertHub>(new RecordingHubClients());
+
+        var poller = new FleetStatusPoller(
+            _sp.GetRequiredService<IServiceScopeFactory>(),
+            fleetHub, alertHub, NullLogger<FleetStatusPoller>.Instance, new RedundancyMetrics());
+
+        await poller.PollOnceAsync(CancellationToken.None);
+
+        var match = recorder.SentMessages.FirstOrDefault(m =>
+            m.Method == "ResilienceStatusChanged" &&
+            m.Args.Length > 0 &&
+            m.Args[0] is ResilienceStatusChangedMessage r &&
+            r.DriverInstanceId == "drv-1" && r.HostName == "plc.example.com");
+        match.ShouldNotBeNull("poller should have pushed ResilienceStatusChanged on first observation");
+
+        // Same snapshot on the next tick — should NOT push again (delta-only push).
+        recorder.SentMessages.Clear();
+        await poller.PollOnceAsync(CancellationToken.None);
+        recorder.SentMessages.Any(m => m.Method == "ResilienceStatusChanged")
+            .ShouldBeFalse("unchanged snapshot must not fire another push");
+
+        // Mutate the row — delta should fire again.
+        using (var scope = _sp.CreateScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<OtOpcUaConfigDbContext>();
+            var row = await db.DriverInstanceResilienceStatuses.SingleAsync();
+            row.ConsecutiveFailures = 5;
+            row.LastCircuitBreakerOpenUtc = DateTime.UtcNow;
+            await db.SaveChangesAsync();
+        }
+
+        await poller.PollOnceAsync(CancellationToken.None);
+        var mutatedMatch = recorder.SentMessages.FirstOrDefault(m =>
+            m.Method == "ResilienceStatusChanged" &&
+            m.Args.Length > 0 &&
+            m.Args[0] is ResilienceStatusChangedMessage r2 && r2.ConsecutiveFailures == 5);
+        mutatedMatch.ShouldNotBeNull("mutated row should produce a second ResilienceStatusChanged");
+    }
 }