Phase 6.1 Stream E.3 partial — in-flight counter feeds CurrentBulkheadDepth

Closes the observer half of #162 that was flagged as "persisted as 0 today"
in PR #105. The Admin /hosts column refresh + FleetStatusHub SignalR push
+ red-badge visual still belong to the visual-compliance pass.

Core.Resilience:
- DriverResilienceStatusTracker gains RecordCallStart + RecordCallComplete
  + CurrentInFlight field on the snapshot record. Concurrent-safe via the
  same ConcurrentDictionary.AddOrUpdate pattern as the other recorder methods.
  Clamps to zero on over-decrement so a stray Complete-without-Start can't
  drive the counter negative.
- CapabilityInvoker gains an optional statusTracker ctor parameter. When
  wired, every ExecuteAsync / ExecuteAsync(void) wraps the pipeline call
  in try / finally that records start/complete — so the counter advances
  cleanly whether the call succeeds, cancels, or throws. Null tracker keeps
  the pre-Phase-6.1 Stream E.3 behaviour exactly.

Server.Hosting:
- ResilienceStatusPublisherHostedService persists CurrentInFlight as the
  DriverInstanceResilienceStatus.CurrentBulkheadDepth column (was 0 before
  this PR). One-line fix on both the insert + update branches.

The in-flight counter is a pragmatic proxy for Polly's internal bulkhead
depth — a future PR wiring Polly telemetry would replace it with the real
value. The shape of the column + the publisher + the Admin /hosts query
doesn't change, so the follow-up is invisible to consumers.

Tests (8 new InFlightCounterTests, all pass):
- Start+Complete nets to zero.
- Nested starts sum; Complete decrements.
- Complete-without-Start clamps to zero.
- Different hosts track independently.
- Concurrent starts (500 parallel) don't lose count.
- CapabilityInvoker observed-mid-call depth == 1 during a pending call.
- CapabilityInvoker exception path still decrements (try/finally).
- CapabilityInvoker without tracker doesn't throw.

Full solution dotnet test: 1243 passing (was 1235, +8). Pre-existing
Client.CLI Subscribe flake unchanged.

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

src/ZB.MOM.WW.OtOpcUa.Core/Resilience/CapabilityInvoker.cs

@@ -22,6 +22,7 @@ public sealed class CapabilityInvoker
     private readonly string _driverInstanceId;
     private readonly string _driverType;
     private readonly Func<DriverResilienceOptions> _optionsAccessor;
+    private readonly DriverResilienceStatusTracker? _statusTracker;
 
     /// <summary>
     ///     Construct an invoker for one driver instance.
@@ -33,11 +34,13 @@ public sealed class CapabilityInvoker
     ///     pipeline-invalidate can take effect without restarting the invoker.
     /// </param>
     /// <param name="driverType">Driver type name for structured-log enrichment (e.g. <c>"Modbus"</c>).</param>
+    /// <param name="statusTracker">Optional resilience-status tracker. When wired, every capability call records start/complete so Admin <c>/hosts</c> can surface <see cref="ResilienceStatusSnapshot.CurrentInFlight"/> as the bulkhead-depth proxy.</param>
     public CapabilityInvoker(
         DriverResiliencePipelineBuilder builder,
         string driverInstanceId,
         Func<DriverResilienceOptions> optionsAccessor,
-        string driverType = "Unknown")
+        string driverType = "Unknown",
+        DriverResilienceStatusTracker? statusTracker = null)
     {
         ArgumentNullException.ThrowIfNull(builder);
         ArgumentNullException.ThrowIfNull(optionsAccessor);
@@ -46,6 +49,7 @@ public sealed class CapabilityInvoker
         _driverInstanceId = driverInstanceId;
         _driverType = driverType;
         _optionsAccessor = optionsAccessor;
+        _statusTracker = statusTracker;
     }
 
     /// <summary>Execute a capability call returning a value, honoring the per-capability pipeline.</summary>
@@ -59,9 +63,17 @@ public sealed class CapabilityInvoker
         ArgumentNullException.ThrowIfNull(callSite);
 
         var pipeline = ResolvePipeline(capability, hostName);
-        using (LogContextEnricher.Push(_driverInstanceId, _driverType, capability, LogContextEnricher.NewCorrelationId()))
+        _statusTracker?.RecordCallStart(_driverInstanceId, hostName);
+        try
         {
-            return await pipeline.ExecuteAsync(callSite, cancellationToken).ConfigureAwait(false);
+            using (LogContextEnricher.Push(_driverInstanceId, _driverType, capability, LogContextEnricher.NewCorrelationId()))
+            {
+                return await pipeline.ExecuteAsync(callSite, cancellationToken).ConfigureAwait(false);
+            }
+        }
+        finally
+        {
+            _statusTracker?.RecordCallComplete(_driverInstanceId, hostName);
         }
     }
 
@@ -75,9 +87,17 @@ public sealed class CapabilityInvoker
         ArgumentNullException.ThrowIfNull(callSite);
 
         var pipeline = ResolvePipeline(capability, hostName);
-        using (LogContextEnricher.Push(_driverInstanceId, _driverType, capability, LogContextEnricher.NewCorrelationId()))
+        _statusTracker?.RecordCallStart(_driverInstanceId, hostName);
+        try
         {
-            await pipeline.ExecuteAsync(callSite, cancellationToken).ConfigureAwait(false);
+            using (LogContextEnricher.Push(_driverInstanceId, _driverType, capability, LogContextEnricher.NewCorrelationId()))
+            {
+                await pipeline.ExecuteAsync(callSite, cancellationToken).ConfigureAwait(false);
+            }
+        }
+        finally
+        {
+            _statusTracker?.RecordCallComplete(_driverInstanceId, hostName);
         }
     }