feat(localdb): telemetry meters + ISyncStatus

Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts

ZB.MOM.WW.LocalDb/src/ZB.MOM.WW.LocalDb.Replication/Internal/SyncSession.cs

@@ -31,6 +31,8 @@ internal sealed class SyncSession
     private readonly ReplicationOptions _options;
     private readonly ILogger _logger;
     private readonly Func<DateTimeOffset> _utcNow;
+    private readonly LocalDbMetrics? _metrics;
+    private readonly SyncStatus? _status;
 
     // Highest oplog seq handed to the wire this session; the pump reads strictly above it so a batch
     // is never re-sent before its ack (the reliable ordered stream delivers exactly once in-session).
@@ -45,7 +47,7 @@ internal sealed class SyncSession
 
     public SyncSession(
         SqliteLocalDb db, OplogStore store, LwwApplier applier, ReplicationOptions options, ILogger logger,
-        Func<DateTimeOffset>? utcNow = null)
+        Func<DateTimeOffset>? utcNow = null, LocalDbMetrics? metrics = null, SyncStatus? status = null)
     {
         _db = db;
         _store = store;
@@ -53,6 +55,8 @@ internal sealed class SyncSession
         _options = options;
         _logger = logger;
         _utcNow = utcNow ?? (() => DateTimeOffset.UtcNow);
+        _metrics = metrics;
+        _status = status;
     }
 
     /// <summary>
@@ -140,6 +144,7 @@ internal sealed class SyncSession
 
         await _store.SetPeerNodeIdAsync(peerHandshake.NodeId, ct);
         PeerNodeId = peerHandshake.NodeId;
+        _status?.SetPeerNodeId(peerHandshake.NodeId);
         _sentThruSeq = peerHandshake.LastAppliedRemoteSeq;
         Interlocked.Exchange(ref _peerAckedSeq, peerHandshake.LastAppliedRemoteSeq);
 
@@ -164,6 +169,7 @@ internal sealed class SyncSession
             if (SnapshotSender is null)
                 throw new NotSupportedException("snapshot required but no snapshot sender configured");
             var snapshotAsOfSeq = await SnapshotSender(dataSend, ct);
+            _metrics?.RecordSnapshot("sent");
             // The snapshot already carries every row state up to as-of; skipping the pump past it
             // avoids re-sending tail deltas the peer would only discard via LWW.
             if (snapshotAsOfSeq > _sentThruSeq)
@@ -269,6 +275,7 @@ internal sealed class SyncSession
                                 "Replication protocol error: SnapshotComplete with no active snapshot (missing SnapshotBegin).");
                         await SnapshotApplier!.OnCompleteAsync(msg.SnapshotComplete, ct);
                         _snapshotReceiving = false;
+                        _metrics?.RecordSnapshot("received");
                         break;
                     default:
                         throw new InvalidOperationException(
@@ -288,6 +295,7 @@ internal sealed class SyncSession
         var driftLimitMs = nowMs + (long)_options.MaxHlcDriftAhead.TotalMilliseconds;
         var toApply = new List<OplogEntryRecord>(batch.Entries.Count);
         var maxSeq = 0L;
+        var driftDeadLettered = 0;
 
         foreach (var proto in batch.Entries)
         {
@@ -310,6 +318,7 @@ internal sealed class SyncSession
                 if (_options.FailClosedOnDrift)
                 {
                     await DeadLetterDriftedAsync(entry, physicalMs, nowMs, now, ct);
+                    driftDeadLettered++;
                     continue;
                 }
             }
@@ -317,6 +326,10 @@ internal sealed class SyncSession
         }
 
         var result = await _applier.ApplyBatchAsync(toApply, ct);
+        _metrics?.RecordApplied(result.Applied);
+        _metrics?.RecordConflictsDiscarded(result.Discarded);
+        _metrics?.RecordDeadLettered(result.DeadLettered + driftDeadLettered);
+        _status?.SetLastSyncUtc(now);
         var ackThru = Math.Max(result.AppliedThruSeq, maxSeq);
         if (ackThru > result.AppliedThruSeq)
             // Dead-lettered entries carried the batch's top seqs; advance the durable remote