fix(localdb): snapshot review fixes — MAX-guarded complete watermark, keyset pagination, phantom-row guard

Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts
2026-07-17 23:50:42 -04:00
parent 130e9c918f
commit 8befebd476
5 changed files with 135 additions and 23 deletions
@@ -146,10 +146,15 @@ internal sealed class OplogStore(ILocalDb db, ReplicationOptions options, Func<D
    public Task SetNeedsSnapshotAsync(bool value, CancellationToken ct = default) =>
        db.ExecuteAsync("UPDATE __localdb_peer_state SET needs_snapshot = @v WHERE id = 1", new { v = value ? 1 : 0 }, ct);

-    /// <summary>Records the highest remote seq applied locally plus the peer HLC observed with it; also stamps <c>last_sync_utc</c>.</summary>
+    /// <summary>
+    /// Records the highest remote seq applied locally plus the peer HLC observed with it; also stamps
+    /// <c>last_sync_utc</c>. Both watermarks are MAX-guarded (monotonic): a snapshot completing with a
+    /// lower as-of seq than a concurrently-applied delta must never regress the durable watermark.
+    /// </summary>
    public Task SetLastAppliedRemoteSeqAsync(long seq, long lastSeenHlc, CancellationToken ct = default) =>
        db.ExecuteAsync(
-            "UPDATE __localdb_peer_state SET last_applied_remote_seq = @seq, last_seen_hlc = @hlc, last_sync_utc = @now WHERE id = 1",
+            "UPDATE __localdb_peer_state SET last_applied_remote_seq = MAX(last_applied_remote_seq, @seq), " +
+            "last_seen_hlc = MAX(last_seen_hlc, @hlc), last_sync_utc = @now WHERE id = 1",
            new { seq, hlc = lastSeenHlc, now = FormatUtc(_utcNow()) }, ct);

    private static string FormatUtc(DateTimeOffset value) =>