fix(mcp): harden dashboard dispatch lifecycle

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

cmd/dashboard/controller/websocket_ping.go

@@ -0,0 +1,79 @@
+package controller
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+type websocketPingWriter interface {
+	WriteMessage(messageType int, data []byte) error
+}
+
+type websocketPingConnection interface {
+	websocketPingWriter
+	Close() error
+}
+
+type websocketPingTransport struct {
+	websocketPingWriter
+	closeOnce sync.Once
+	closeErr  error
+	close     func() error
+}
+
+func newWebsocketPingTransport(writer websocketPingWriter, close func() error) *websocketPingTransport {
+	return &websocketPingTransport{websocketPingWriter: writer, close: close}
+}
+
+func (transport *websocketPingTransport) Close() error {
+	transport.closeOnce.Do(func() { transport.closeErr = transport.close() })
+	return transport.closeErr
+}
+
+func websocketPingLoop(ctx context.Context, ticks <-chan time.Time, writer websocketPingWriter) error {
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case _, ok := <-ticks:
+			if !ok {
+				return nil
+			}
+		}
+
+		select {
+		case <-ctx.Done():
+			return nil
+		default:
+		}
+		if err := writer.WriteMessage(websocket.PingMessage, []byte{}); err != nil {
+			return err
+		}
+	}
+}
+
+func startWebsocketPing(ctx context.Context, ticks <-chan time.Time, connection websocketPingConnection) func() {
+	workerContext, cancel := context.WithCancel(ctx)
+	workerDone := make(chan struct{})
+	go func() {
+		defer close(workerDone)
+		_ = websocketPingLoop(workerContext, ticks, connection)
+	}()
+	return func() {
+		_ = connection.Close()
+		cancel()
+		<-workerDone
+	}
+}
+
+func startWebsocketPingTicker(ctx context.Context, interval time.Duration, connection websocketPingConnection) func() {
+	ticker := time.NewTicker(interval)
+	stop := startWebsocketPing(ctx, ticker.C, connection)
+	return func() {
+		ticker.Stop()
+		stop()
+	}
+}