fix(quic): exclude locally rejected datagrams [CI]

backend/probe/src/MoShiro.Probe/Link/AgentConnection.cs

@@ -51,7 +51,7 @@ public sealed class AgentConnection : IDisposable
 
     public KnownAgent Endpoint { get; }
 
-    public bool IsConnected => _session is not null;
+    public bool IsConnected => _session is not null && Volatile.Read(ref _activeDatagrams)?.IsConnected == true;
 
     public int RoleCount => _session?.RoleCount ?? 0;
 
@@ -91,16 +91,26 @@ public sealed class AgentConnection : IDisposable
                 p95 = sorted[(int)Math.Ceiling(sorted.Length * 0.95) - 1];
             }
 
-            QuicTransportSnapshot? transport = Volatile.Read(ref _activeDatagrams)?.GetTransportSnapshot();
+            QuicDatagramTransport? datagrams = Volatile.Read(ref _activeDatagrams);
+            bool connected = _session is not null && datagrams?.IsConnected == true;
+            ProbeLinkAttemptState state = _attemptState;
+            string? lastError = _lastError;
+            if (!connected && state == ProbeLinkAttemptState.Connected)
+            {
+                state = ProbeLinkAttemptState.RetryWait;
+                lastError ??= "QUIC datagram transport is closed; reconnecting";
+            }
+
+            QuicTransportSnapshot? transport = datagrams?.GetTransportSnapshot();
             return new ProbeQuicLinkHealth
             {
                 AgentId = Endpoint.AgentId,
                 IpVersion = Endpoint.IpVersion,
-                Connected = IsConnected,
-                State = _attemptState,
-                LastError = _lastError,
+                Connected = connected,
+                State = state,
+                LastError = lastError,
                 RetryAttempt = _lastRetryAttempt,
-                RetryInMs = _attemptState == ProbeLinkAttemptState.RetryWait && _retryAt is { } retryAt
+                RetryInMs = state == ProbeLinkAttemptState.RetryWait && _retryAt is { } retryAt
                     ? Math.Max(0, (long)(retryAt - _env.Time.GetUtcNow()).TotalMilliseconds)
                     : null,
                 HandshakeAttempts = _handshakeAttempts,
@@ -282,9 +292,21 @@ public sealed class AgentConnection : IDisposable
             _env.Log.Info("agent session up", ("agent", Endpoint.AgentId), ("offset_us", clock.OffsetUs));
             Task maintenance = MaintainAsync(rpc, session, clock, cts.Token);
             Task finished = await Task.WhenAny(run, receive, pump, maintenance);
+            string reason = finished == run
+                ? "closed by the Agent control connection"
+                : finished == receive
+                    ? "QUIC datagram transport closed"
+                    : finished == pump
+                        ? "Probe outbox pump stopped"
+                        : "connection maintenance stopped";
+            if (finished.IsFaulted && finished.Exception?.GetBaseException() is { } error)
+            {
+                reason = $"{error.GetType().Name}: {error.Message}";
+            }
+
             await cts.CancelAsync();
             await Task.WhenAll(Quiet(run), Quiet(receive), Quiet(pump), Quiet(maintenance));
-            return finished == run ? "closed by the agent" : "session task failed";
+            return reason;
         }
         finally
         {