fix: handle forward service rebind on self-occupied port

When UpdateService encounters bind address conflicts (port already in use),
the handler now automatically deletes existing forward services and retries
the AddService operation. This resolves issues where a forward's own stale
listener prevents the update.

- Add isBindAddressInUseError() to detect port bind conflicts
- Add rebindForwardServiceOnSelfOccupiedPort() for automatic cleanup and retry
- Add HasOtherForwardOnNodePort() repository method to verify port ownership
- Add unit tests for bind conflict detection

go-backend/internal/http/handler/control_plane.go

@@ -286,6 +286,9 @@ func (h *Handler) syncForwardServices(forward *forwardRecord, method string, all
 		if err != nil && allowFallbackAdd && method == "UpdateService" {
 			_, err = h.sendNodeCommand(node.ID, "AddService", services, true, false)
 		}
+		if err != nil && strings.EqualFold(strings.TrimSpace(method), "UpdateService") && isBindAddressInUseError(err) {
+			err = h.rebindForwardServiceOnSelfOccupiedPort(forward, node, fp.Port, services)
+		}
 		if err != nil {
 			return fmt.Errorf("节点 %s 下发失败: %w", node.Name, err)
 		}
@@ -293,6 +296,77 @@ func (h *Handler) syncForwardServices(forward *forwardRecord, method string, all
 	return nil
 }
 
+func (h *Handler) rebindForwardServiceOnSelfOccupiedPort(forward *forwardRecord, node *nodeRecord, port int, services []map[string]interface{}) error {
+	if h == nil || forward == nil || node == nil {
+		return errors.New("invalid self-occupy rebind context")
+	}
+	if port <= 0 {
+		return errors.New("invalid forward port")
+	}
+
+	hasOtherForward, err := h.repo.HasOtherForwardOnNodePort(node.ID, port, forward.ID)
+	if err != nil {
+		return err
+	}
+	if hasOtherForward {
+		return fmt.Errorf("端口 %d 已被其他转发占用", port)
+	}
+
+	if err := h.deleteForwardServicesOnNode(forward, node.ID); err != nil {
+		return err
+	}
+
+	time.Sleep(150 * time.Millisecond)
+
+	_, err = h.sendNodeCommand(node.ID, "AddService", services, true, false)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (h *Handler) deleteForwardServicesOnNode(forward *forwardRecord, nodeID int64) error {
+	if h == nil || forward == nil {
+		return errors.New("invalid forward delete context")
+	}
+
+	userTunnelID, _, _, err := h.resolveUserTunnelAndLimiter(forward.UserID, forward.TunnelID)
+	if err != nil {
+		return err
+	}
+	userTunnelIDs, err := h.listUserTunnelIDs(forward.UserID, forward.TunnelID)
+	if err != nil {
+		return err
+	}
+	allUserTunnelIDs, err := h.listUserTunnelIDsByUser(forward.UserID)
+	if err != nil {
+		return err
+	}
+	candidateTunnelIDs := make([]int64, 0, len(userTunnelIDs)+len(allUserTunnelIDs))
+	candidateTunnelIDs = append(candidateTunnelIDs, userTunnelIDs...)
+	candidateTunnelIDs = append(candidateTunnelIDs, allUserTunnelIDs...)
+	bases := buildForwardServiceBaseCandidates(forward.ID, forward.UserID, userTunnelID, candidateTunnelIDs)
+
+	var lastErr error
+	for _, base := range bases {
+		names := buildForwardControlServiceNames(base, "DeleteService")
+		payload := map[string]interface{}{
+			"services": names,
+		}
+		_, cmdErr := h.sendNodeCommand(nodeID, "DeleteService", payload, false, true)
+		if cmdErr == nil {
+			return nil
+		}
+		lastErr = cmdErr
+	}
+
+	if lastErr != nil {
+		return lastErr
+	}
+	return nil
+}
+
 func (h *Handler) controlForwardServices(forward *forwardRecord, commandType string, tolerateNotFound bool) error {
 	if h == nil || forward == nil {
 		return errors.New("invalid forward control context")
@@ -1303,6 +1377,20 @@ func isAlreadyExistsMessage(message string) bool {
 	return strings.Contains(msg, "already exists") || strings.Contains(msg, "已存在")
 }
 
+func isBindAddressInUseError(err error) bool {
+	if err == nil {
+		return false
+	}
+	msg := strings.ToLower(strings.TrimSpace(err.Error()))
+	if msg == "" {
+		return false
+	}
+	if strings.Contains(msg, "address already in use") {
+		return true
+	}
+	return strings.Contains(msg, "cannot assign requested address")
+}
+
 func buildForwardServiceConfigs(baseName string, forward *forwardRecord, tunnel *tunnelRecord, node *nodeRecord, port int, bindIP string, limiterID *int64, tunnelTLSProtocol bool) []map[string]interface{} {
 	protocols := []string{"tcp", "udp"}
 	services := make([]map[string]interface{}, 0, 2)

go-backend/internal/http/handler/control_plane_test.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"errors"
 	"reflect"
 	"testing"
 )
@@ -66,6 +67,21 @@ func TestIsAlreadyExistsMessage(t *testing.T) {
 	}
 }
 
+func TestIsBindAddressInUseError(t *testing.T) {
+	if !isBindAddressInUseError(errors.New("listen tcp [::]:10001: bind: address already in use")) {
+		t.Fatalf("address already in use should be detected")
+	}
+	if !isBindAddressInUseError(errors.New("listen tcp4 13.228.170.187:16765: bind: cannot assign requested address")) {
+		t.Fatalf("cannot assign requested address should be detected")
+	}
+	if isBindAddressInUseError(errors.New("service demo already exists")) {
+		t.Fatalf("already exists should not be treated as bind conflict")
+	}
+	if isBindAddressInUseError(nil) {
+		t.Fatalf("nil error should not be treated as bind conflict")
+	}
+}
+
 func TestBuildForwardServiceConfigs_UsesBindIPForListen(t *testing.T) {
 	forward := &forwardRecord{RemoteAddr: "1.2.3.4:80", Strategy: "fifo", TunnelID: 7}
 	node := &nodeRecord{TCPListenAddr: "[::]", UDPListenAddr: "[::]"}

go-backend/internal/store/repo/repository_control.go

@@ -111,6 +111,25 @@ func (r *Repository) ListForwardPorts(forwardID int64) ([]model.ForwardPortRecor
 	return rows, nil
 }
 
+func (r *Repository) HasOtherForwardOnNodePort(nodeID int64, port int, currentForwardID int64) (bool, error) {
+	if r == nil || r.db == nil {
+		return false, errors.New("repository not initialized")
+	}
+	if nodeID <= 0 || port <= 0 {
+		return false, nil
+	}
+
+	var count int64
+	err := r.db.Model(&model.ForwardPort{}).
+		Where("node_id = ? AND port = ? AND forward_id <> ?", nodeID, port, currentForwardID).
+		Count(&count).Error
+	if err != nil {
+		return false, err
+	}
+
+	return count > 0, nil
+}
+
 func (r *Repository) GetTunnelOutProtocol(tunnelID int64) (string, error) {
 	if r == nil || r.db == nil {
 		return "", errors.New("repository not initialized")

plans/004-forward-explicit-bind-self-occupy-release.md

@@ -0,0 +1,11 @@
+# 004 Forward Explicit Bind Self-Occupy Release
+
+## Checklist
+
+- [x] Confirm current forward edit/save failure path and lock strategy: explicit bind always stays explicit.
+- [x] Add repository query to detect whether a node+port is occupied by other forwards (excluding current forward).
+- [x] Enhance forward service sync to treat address-in-use as a recoverable case when only self occupies the port.
+- [x] On self-occupy conflict, proactively delete current forward services on target node and retry AddService.
+- [x] Keep hard failure when the same node+port is occupied by other forwards.
+- [x] Add focused unit tests for new error classification helpers.
+- [x] Run focused backend tests for touched handler/repo packages.