feat: add websocket routing and executor unregister API

- Introduce Server.AttachWebsocketRoute(path, handler) to mount websocket
  upgrade handlers on the Gin engine.
- Track registered WS paths via wsRoutes with wsRouteMu to prevent
  duplicate registrations; initialize in NewServer and import sync.
- Add Manager.UnregisterExecutor(provider) for clean executor lifecycle
  management.
- Add github.com/gorilla/websocket v1.5.3 dependency and update go.sum.

Motivation: enable services to expose WS endpoints through the core server
and allow removing auth executors dynamically while avoiding duplicate
route setup. No breaking changes.

internal/wsrelay/session.go

@@ -0,0 +1,188 @@
+package wsrelay
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+const (
+	readTimeout          = 60 * time.Second
+	writeTimeout         = 10 * time.Second
+	maxInboundMessageLen = 64 << 20 // 64 MiB
+	heartbeatInterval    = 30 * time.Second
+)
+
+var errClosed = errors.New("websocket session closed")
+
+type pendingRequest struct {
+	ch        chan Message
+	closeOnce sync.Once
+}
+
+func (pr *pendingRequest) close() {
+	if pr == nil {
+		return
+	}
+	pr.closeOnce.Do(func() {
+		close(pr.ch)
+	})
+}
+
+type session struct {
+	conn       *websocket.Conn
+	manager    *Manager
+	provider   string
+	id         string
+	closed     chan struct{}
+	closeOnce  sync.Once
+	writeMutex sync.Mutex
+	pending    sync.Map // map[string]*pendingRequest
+}
+
+func newSession(conn *websocket.Conn, mgr *Manager, id string) *session {
+	s := &session{
+		conn:     conn,
+		manager:  mgr,
+		provider: "",
+		id:       id,
+		closed:   make(chan struct{}),
+	}
+	conn.SetReadLimit(maxInboundMessageLen)
+	conn.SetReadDeadline(time.Now().Add(readTimeout))
+	conn.SetPongHandler(func(string) error {
+		conn.SetReadDeadline(time.Now().Add(readTimeout))
+		return nil
+	})
+	s.startHeartbeat()
+	return s
+}
+
+func (s *session) startHeartbeat() {
+	if s == nil || s.conn == nil {
+		return
+	}
+	ticker := time.NewTicker(heartbeatInterval)
+	go func() {
+		defer ticker.Stop()
+		for {
+			select {
+			case <-s.closed:
+				return
+			case <-ticker.C:
+				s.writeMutex.Lock()
+				err := s.conn.WriteControl(websocket.PingMessage, []byte("ping"), time.Now().Add(writeTimeout))
+				s.writeMutex.Unlock()
+				if err != nil {
+					s.cleanup(err)
+					return
+				}
+			}
+		}
+	}()
+}
+
+func (s *session) run(ctx context.Context) {
+	defer s.cleanup(errClosed)
+	for {
+		var msg Message
+		if err := s.conn.ReadJSON(&msg); err != nil {
+			s.cleanup(err)
+			return
+		}
+		s.dispatch(msg)
+	}
+}
+
+func (s *session) dispatch(msg Message) {
+	if msg.Type == MessageTypePing {
+		_ = s.send(context.Background(), Message{ID: msg.ID, Type: MessageTypePong})
+		return
+	}
+	if value, ok := s.pending.Load(msg.ID); ok {
+		req := value.(*pendingRequest)
+		select {
+		case req.ch <- msg:
+		default:
+		}
+		if msg.Type == MessageTypeHTTPResp || msg.Type == MessageTypeError || msg.Type == MessageTypeStreamEnd {
+			if actual, loaded := s.pending.LoadAndDelete(msg.ID); loaded {
+				actual.(*pendingRequest).close()
+			}
+		}
+		return
+	}
+	if msg.Type == MessageTypeHTTPResp || msg.Type == MessageTypeError || msg.Type == MessageTypeStreamEnd {
+		s.manager.logDebugf("wsrelay: received terminal message for unknown id %s (provider=%s)", msg.ID, s.provider)
+	}
+}
+
+func (s *session) send(ctx context.Context, msg Message) error {
+	select {
+	case <-s.closed:
+		return errClosed
+	default:
+	}
+	s.writeMutex.Lock()
+	defer s.writeMutex.Unlock()
+	if err := s.conn.SetWriteDeadline(time.Now().Add(writeTimeout)); err != nil {
+		return fmt.Errorf("set write deadline: %w", err)
+	}
+	if err := s.conn.WriteJSON(msg); err != nil {
+		return fmt.Errorf("write json: %w", err)
+	}
+	return nil
+}
+
+func (s *session) request(ctx context.Context, msg Message) (<-chan Message, error) {
+	if msg.ID == "" {
+		return nil, fmt.Errorf("wsrelay: message id is required")
+	}
+	if _, loaded := s.pending.LoadOrStore(msg.ID, &pendingRequest{ch: make(chan Message, 8)}); loaded {
+		return nil, fmt.Errorf("wsrelay: duplicate message id %s", msg.ID)
+	}
+	value, _ := s.pending.Load(msg.ID)
+	req := value.(*pendingRequest)
+	if err := s.send(ctx, msg); err != nil {
+		if actual, loaded := s.pending.LoadAndDelete(msg.ID); loaded {
+			req := actual.(*pendingRequest)
+			req.close()
+		}
+		return nil, err
+	}
+	go func() {
+		select {
+		case <-ctx.Done():
+			if actual, loaded := s.pending.LoadAndDelete(msg.ID); loaded {
+				actual.(*pendingRequest).close()
+			}
+		case <-s.closed:
+		}
+	}()
+	return req.ch, nil
+}
+
+func (s *session) cleanup(cause error) {
+	s.closeOnce.Do(func() {
+		close(s.closed)
+		s.pending.Range(func(key, value any) bool {
+			req := value.(*pendingRequest)
+			msg := Message{ID: key.(string), Type: MessageTypeError, Payload: map[string]any{"error": cause.Error()}}
+			select {
+			case req.ch <- msg:
+			default:
+			}
+			req.close()
+			return true
+		})
+		s.pending = sync.Map{}
+		_ = s.conn.Close()
+		if s.manager != nil {
+			s.manager.handleSessionClosed(s, cause)
+		}
+	})
+}