feat(saf): resync ack confirmation + completed/ack-missing telemetry; doc resync rewrite (plan R2-02 T7)

src/ZB.MOM.WW.ScadaBridge.Commons/Observability/ScadaBridgeTelemetry.cs

@@ -47,6 +47,14 @@ public static class ScadaBridgeTelemetry
         Meter.CreateCounter<long>("scadabridge.store_and_forward.replication.failures", unit: "1",
             description: "S&F buffer replication operations that failed to dispatch/deliver to the peer node");
 
+    private static readonly Counter<long> _sfResyncCompleted =
+        Meter.CreateCounter<long>("scadabridge.store_and_forward.resync.completed", unit: "1",
+            description: "S&F anti-entropy resyncs the standby acknowledged as applied");
+
+    private static readonly Counter<long> _sfResyncAckMissing =
+        Meter.CreateCounter<long>("scadabridge.store_and_forward.resync.ack_missing", unit: "1",
+            description: "S&F resyncs answered by the active node but never acknowledged by the standby within the ack window (lost chunks / dead peer)");
+
     /// <summary>
     /// Incremented each time a per-site live-alarm aggregator re-establishes its site-wide
     /// gRPC stream — a NodeA↔NodeB failover flip or a reconcile-driven reopen after the
@@ -107,6 +115,12 @@ public static class ScadaBridgeTelemetry
     /// <summary>Records one failed S&amp;F replication dispatch.</summary>
     public static void RecordReplicationFailure() => _replicationFailures.Add(1);
 
+    /// <summary>Records one acknowledged (applied) S&amp;F buffer resync.</summary>
+    public static void RecordSfResyncCompleted() => _sfResyncCompleted.Add(1);
+
+    /// <summary>Records one resync whose ack window expired.</summary>
+    public static void RecordSfResyncAckMissing() => _sfResyncAckMissing.Add(1);
+
     /// <summary>Records that a site connection opened (increments the up-count gauge).</summary>
     public static void SiteConnectionOpened() => Interlocked.Increment(ref _siteConnectionsUp);