pool/worker: add EventDialFailed with per-attempt error

pool.go

@@ -28,12 +28,14 @@ type PoolEventKind string
 const (
 	EventConnected    PoolEventKind = "connected"
 	EventDisconnected PoolEventKind = "disconnected"
+	EventDialFailed   PoolEventKind = "dial_failed"
 )
 
 type PoolEvent struct {
 	ID   string
 	Kind PoolEventKind
 	At   time.Time
+	Err  error
 }
 
 type PoolStats struct {

worker.go

@@ -311,8 +311,15 @@ func (w *DefaultWorker) spawnDialer(
 		w.logger.Debug("session: dialing")
 	}
 
+	onDialError := func(err error) {
+		if dialCtx.Err() != nil {
+			return
+		}
+		pool.Events <- PoolEvent{ID: w.id, Kind: EventDialFailed, Err: err, At: time.Now()}
+	}
+
 	go func() {
-		conn, err := connect(w.id, dialCtx, pool, w.handler)
+		conn, err := connect(w.id, dialCtx, pool, w.handler, onDialError)
 
 		if err != nil {
 			return
@@ -333,13 +340,14 @@ func connect(
 	ctx context.Context,
 	pool PoolPlugin,
 	handler slog.Handler,
+	onDialError func(error),
 ) (*transport.Connection, error) {
 	cc := pool.ConnectionConfig
 	conn, err := transport.NewConnection(ctx, id, &cc, handler)
 	if err != nil {
 		return nil, err
 	}
-	return conn, conn.Connect(ctx, nil)
+	return conn, conn.Connect(ctx, onDialError)
 }
 
 // ---------------------------/

worker_test.go

@@ -103,12 +103,12 @@ func TestWorkerSession(t *testing.T) {
 
 		honeybeetest.Never(t, func() bool {
 			select {
-			case <-events:
-				return true
+			case e := <-events:
+				return e.Kind == EventConnected || e.Kind == EventDisconnected
 			default:
 				return false
 			}
-		}, "expected no events when dial fails")
+		}, "expected no connected/disconnected events when dial fails")
 
 		// worker goroutine is still running
 		assert.False(t, func() bool {
@@ -639,6 +639,161 @@ func TestWorkerSession(t *testing.T) {
 			}
 		}, "expected wg to drain after parent cancel")
 	})
+
+	t.Run("EventDialFailed emitted with correct ID, non-nil Err, and non-zero At when dialer fails", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		w := makeWorker(t, ctx, cancel)
+		_, events, pool := makeWorkerContext(t)
+
+		cc, _ := transport.NewConnectionConfig(transport.WithRetryDisabled())
+		pool.ConnectionConfig = *cc
+		dialErr := errors.New("connection refused")
+		pool.ConnectionConfig.Dialer = &honeybeetest.MockDialer{
+			DialContextFunc: func(context.Context, string, http.Header) (types.Socket, *http.Response, error) {
+				return nil, nil, dialErr
+			},
+		}
+
+		var wg sync.WaitGroup
+		wg.Go(func() { w.Start(pool) })
+
+		honeybeetest.Eventually(t, func() bool {
+			select {
+			case e := <-events:
+				return e.Kind == EventDialFailed &&
+					e.ID == w.id &&
+					e.Err != nil &&
+					!e.At.IsZero()
+			default:
+				return false
+			}
+		}, "expected EventDialFailed")
+	})
+
+	t.Run("no EventDialFailed when first dial succeeds", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		w := makeWorker(t, ctx, cancel)
+		_, events, pool := makeWorkerContext(t)
+		mockSocket := honeybeetest.NewMockSocket()
+		pool.ConnectionConfig.Dialer = mockDialer(mockSocket)
+
+		var wg sync.WaitGroup
+		wg.Go(func() { w.Start(pool) })
+
+		honeybeetest.Eventually(t, func() bool {
+			select {
+			case e := <-events:
+				return e.Kind == EventConnected
+			default:
+				return false
+			}
+		}, "expected EventConnected")
+
+		// drain any remaining events and assert none are EventDialFailed
+		honeybeetest.Never(t, func() bool {
+			select {
+			case e := <-events:
+				return e.Kind == EventDialFailed
+			default:
+				return false
+			}
+		}, "expected no EventDialFailed when first dial succeeds")
+	})
+
+	t.Run("no EventDialFailed when worker is stopped mid-dial", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		w := makeWorker(t, ctx, cancel)
+		_, events, pool := makeWorkerContext(t)
+
+		cc, _ := transport.NewConnectionConfig(transport.WithRetryDisabled())
+		pool.ConnectionConfig = *cc
+		pool.ConnectionConfig.Dialer = &honeybeetest.MockDialer{
+			DialContextFunc: func(dialCtx context.Context, _ string, _ http.Header) (types.Socket, *http.Response, error) {
+				<-dialCtx.Done()
+				return nil, nil, dialCtx.Err()
+			},
+		}
+
+		var wg sync.WaitGroup
+		wg.Go(func() { w.Start(pool) })
+
+		w.Stop()
+
+		done := make(chan struct{})
+		go func() { wg.Wait(); close(done) }()
+		honeybeetest.Eventually(t, func() bool {
+			select {
+			case <-done:
+				return true
+			default:
+				return false
+			}
+		}, "expected worker to exit after Stop")
+
+		honeybeetest.Never(t, func() bool {
+			select {
+			case e := <-events:
+				return e.Kind == EventDialFailed
+			default:
+				return false
+			}
+		}, "expected no EventDialFailed when stopped mid-dial")
+	})
+
+	t.Run("no EventDialFailed when keepalive replaces an in-progress dial", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		config, _ := NewWorkerConfig(
+			WithReconnectDelay(0),
+			WithKeepaliveTimeout(20*time.Millisecond),
+		)
+		w := &DefaultWorker{
+			ctx:            ctx,
+			cancel:         cancel,
+			id:             "wss://test",
+			config:         config,
+			sendHeartbeat:  make(chan struct{}),
+			processedCount: &atomic.Uint64{},
+			outgoingCount:  &atomic.Uint64{},
+			restartCount:   &atomic.Uint64{},
+		}
+		_, events, pool := makeWorkerContext(t)
+
+		var dialCount atomic.Uint64
+		cc, _ := transport.NewConnectionConfig(transport.WithRetryDisabled())
+		pool.ConnectionConfig = *cc
+		pool.ConnectionConfig.Dialer = &honeybeetest.MockDialer{
+			DialContextFunc: func(dialCtx context.Context, _ string, _ http.Header) (types.Socket, *http.Response, error) {
+				dialCount.Add(1)
+				<-dialCtx.Done()
+				return nil, nil, dialCtx.Err()
+			},
+		}
+
+		var wg sync.WaitGroup
+		wg.Go(func() { w.Start(pool) })
+
+		// keepalive fires after 20ms, cancelling the first dial and spawning a second
+		honeybeetest.Eventually(t, func() bool {
+			return dialCount.Load() >= 2
+		}, "expected at least two dial attempts after keepalive fired")
+
+		honeybeetest.Never(t, func() bool {
+			select {
+			case e := <-events:
+				return e.Kind == EventDialFailed
+			default:
+				return false
+			}
+		}, "expected no EventDialFailed when keepalive replaces dial")
+	})
 }
 
 func TestWorkerSend(t *testing.T) {