fix: add retry mechanism for tunnel service bind conflicts (#286)

## Summary
- Add retry logic for tunnel service creation/update when encountering
"address already in use" bind errors
- Automatically cleanup stale service and retry once before failing
- Add comprehensive unit and contract tests for bind conflict scenarios

## Changes
- `mutations.go`: Add `retryTunnelServiceAddWithCleanup` helper and
`addTunnelServiceOnNode` wrapper
- `control_plane_test.go`: Unit tests for retry behavior on address
conflicts
- `dual_stack_test.go`: Test fallback to node listen address
- `forward_contract_test.go`: Contract test for forward update with bind
retry
- `limiter_sync_failure_contract_test.go`: Contract test for tunnel
update with bind retry
- `plans/016-tunnel-runtime-bind-conflict-retry.md`: Implementation plan
document

## Test Plan
- Unit tests verify retry logic executes correctly
- Contract tests validate end-to-end behavior with mock nodes
- All tests pass with race detector enabled

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

@@ -273,6 +273,75 @@ func TestIsCannotAssignRequestedAddressError(t *testing.T) {
 	}
 }
 
+func TestRetryTunnelServiceAddWithCleanupRetriesOnAddressInUse(t *testing.T) {
+	addCalls := 0
+	cleanupCalls := 0
+	err := retryTunnelServiceAddWithCleanup(
+		func() error {
+			addCalls++
+			if addCalls == 1 {
+				return errors.New("listen tcp 10.0.0.1:32000: bind: address already in use")
+			}
+			return nil
+		},
+		func() error {
+			cleanupCalls++
+			return nil
+		},
+		0,
+	)
+	if err != nil {
+		t.Fatalf("expected retry to succeed, got %v", err)
+	}
+	if addCalls != 2 {
+		t.Fatalf("expected 2 add attempts, got %d", addCalls)
+	}
+	if cleanupCalls != 1 {
+		t.Fatalf("expected 1 cleanup attempt, got %d", cleanupCalls)
+	}
+}
+
+func TestRetryTunnelServiceAddWithCleanupSkipsCleanupOnNonBindError(t *testing.T) {
+	addCalls := 0
+	cleanupCalls := 0
+	err := retryTunnelServiceAddWithCleanup(
+		func() error {
+			addCalls++
+			return errors.New("network timeout")
+		},
+		func() error {
+			cleanupCalls++
+			return nil
+		},
+		0,
+	)
+	if err == nil {
+		t.Fatalf("expected hard error")
+	}
+	if addCalls != 1 {
+		t.Fatalf("expected 1 add attempt, got %d", addCalls)
+	}
+	if cleanupCalls != 0 {
+		t.Fatalf("expected 0 cleanup attempts, got %d", cleanupCalls)
+	}
+}
+
+func TestRetryTunnelServiceAddWithCleanupReturnsCleanupError(t *testing.T) {
+	cleanupErr := errors.New("delete failed")
+	err := retryTunnelServiceAddWithCleanup(
+		func() error {
+			return errors.New("listen tcp 10.0.0.1:32000: bind: address already in use")
+		},
+		func() error {
+			return cleanupErr
+		},
+		0,
+	)
+	if !errors.Is(err, cleanupErr) {
+		t.Fatalf("expected cleanup error %v, got %v", cleanupErr, err)
+	}
+}
+
 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/http/handler/dual_stack_test.go

@@ -43,6 +43,19 @@ func TestBuildTunnelChainServiceConfig_UsesConnectIPForListen(t *testing.T) {
 	}
 }
 
+func TestBuildTunnelChainServiceConfig_FallsBackToNodeListenAddr(t *testing.T) {
+	node := &nodeRecord{TCPListenAddr: "10.8.0.5"}
+	chain := tunnelRuntimeNode{Protocol: "tls", Port: 21002}
+	services := buildTunnelChainServiceConfig(99, chain, node)
+	if len(services) != 1 {
+		t.Fatalf("expected 1 service, got %d", len(services))
+	}
+	addr, _ := services[0]["addr"].(string)
+	if addr != "10.8.0.5:21002" {
+		t.Fatalf("expected node listen addr 10.8.0.5:21002, got %q", addr)
+	}
+}
+
 func TestBuildTunnelChainServiceConfig_DefaultListenAddrWhenConnectIPEmpty(t *testing.T) {
 	node := &nodeRecord{TCPListenAddr: "[::]"}
 	chain := tunnelRuntimeNode{Protocol: "tls", Port: 21001}

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

@@ -25,6 +25,8 @@ import (
 	"gorm.io/gorm"
 )
 
+const tunnelServiceBindRetryDelay = 150 * time.Millisecond
+
 func (h *Handler) userCreate(w http.ResponseWriter, r *http.Request) {
 	if r.Method != http.MethodPost {
 		response.WriteJSON(w, response.ErrDefault("请求失败"))
@@ -2584,7 +2586,7 @@ func (h *Handler) applyTunnelRuntime(state *tunnelCreateState) ([]int64, []int64
 			createdChains = append(createdChains, chainNode.NodeID)
 
 			serviceData := buildTunnelChainServiceConfig(state.TunnelID, chainNode, state.Nodes[chainNode.NodeID])
-			if _, err := h.sendNodeCommand(chainNode.NodeID, "AddService", serviceData, true, false); err != nil {
+			if err := h.addTunnelServiceOnNode(chainNode.NodeID, state.TunnelID, serviceData); err != nil {
 				return createdChains, createdServices, fmt.Errorf("转发链节点 %s 下发服务失败: %w", nodeDisplayName(state.Nodes[chainNode.NodeID]), err)
 			}
 			createdServices = append(createdServices, chainNode.NodeID)
@@ -2596,7 +2598,7 @@ func (h *Handler) applyTunnelRuntime(state *tunnelCreateState) ([]int64, []int64
 			continue
 		}
 		serviceData := buildTunnelChainServiceConfig(state.TunnelID, outNode, state.Nodes[outNode.NodeID])
-		if _, err := h.sendNodeCommand(outNode.NodeID, "AddService", serviceData, true, false); err != nil {
+		if err := h.addTunnelServiceOnNode(outNode.NodeID, state.TunnelID, serviceData); err != nil {
 			return createdChains, createdServices, fmt.Errorf("出口节点 %s 下发服务失败: %w", nodeDisplayName(state.Nodes[outNode.NodeID]), err)
 		}
 		createdServices = append(createdServices, outNode.NodeID)
@@ -2605,6 +2607,44 @@ func (h *Handler) applyTunnelRuntime(state *tunnelCreateState) ([]int64, []int64
 	return createdChains, createdServices, nil
 }
 
+func retryTunnelServiceAddWithCleanup(add func() error, cleanup func() error, wait time.Duration) error {
+	if add == nil {
+		return errors.New("invalid tunnel service add callback")
+	}
+	err := add()
+	if err == nil || !isAddressAlreadyInUseError(err) {
+		return err
+	}
+	if cleanup == nil {
+		return err
+	}
+	if cleanupErr := cleanup(); cleanupErr != nil {
+		return cleanupErr
+	}
+	if wait > 0 {
+		time.Sleep(wait)
+	}
+	return add()
+}
+
+func (h *Handler) addTunnelServiceOnNode(nodeID, tunnelID int64, serviceData []map[string]interface{}) error {
+	if h == nil {
+		return errors.New("invalid tunnel service context")
+	}
+	serviceName := fmt.Sprintf("%d_tls", tunnelID)
+	return retryTunnelServiceAddWithCleanup(
+		func() error {
+			_, err := h.sendNodeCommand(nodeID, "AddService", serviceData, true, false)
+			return err
+		},
+		func() error {
+			_, err := h.sendNodeCommand(nodeID, "DeleteService", map[string]interface{}{"services": []string{serviceName}}, false, true)
+			return err
+		},
+		tunnelServiceBindRetryDelay,
+	)
+}
+
 func (h *Handler) rollbackTunnelRuntime(chainNodeIDs, serviceNodeIDs []int64, tunnelID int64) {
 	if h == nil || tunnelID <= 0 {
 		return

go-backend/tests/contract/forward_contract_test.go

@@ -7,6 +7,8 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"strconv"
+	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -914,6 +916,164 @@ func TestForwardCreateThenPauseResumeContract(t *testing.T) {
 	}
 }
 
+func TestForwardUpdateRecoversFromAddressInUseContract(t *testing.T) {
+	secret := "contract-jwt-secret"
+	router, repo := setupContractRouter(t, secret)
+	server := httptest.NewServer(router)
+	defer server.Close()
+
+	adminToken, err := auth.GenerateToken(1, "admin_user", 0, secret)
+	if err != nil {
+		t.Fatalf("generate admin token: %v", err)
+	}
+
+	now := time.Now().UnixMilli()
+	if err := repo.DB().Exec(`
+		INSERT INTO user(id, user, pwd, role_id, exp_time, flow, in_flow, out_flow, flow_reset_time, num, created_time, updated_time, status)
+		VALUES(202, 'forward_bind_retry_user', 'pwd', 1, 2727251700000, 99999, 0, 0, 1, 99999, ?, ?, 1)
+	`, now, now).Error; err != nil {
+		t.Fatalf("insert user: %v", err)
+	}
+
+	if err := repo.DB().Exec(`
+		INSERT INTO tunnel(name, traffic_ratio, type, protocol, flow, created_time, updated_time, status, in_ip, inx)
+		VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`, "forward-bind-retry-tunnel", 1.0, 1, "tls", 99999, now, now, 1, nil, 0).Error; err != nil {
+		t.Fatalf("insert tunnel: %v", err)
+	}
+	tunnelID := mustLastInsertID(t, repo, "forward-bind-retry-tunnel")
+
+	if err := repo.DB().Exec(`
+		INSERT INTO node(name, secret, server_ip, server_ip_v4, server_ip_v6, port, interface_name, version, http, tls, socks, created_time, updated_time, status, tcp_listen_addr, udp_listen_addr, inx)
+		VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`, "forward-bind-retry-node", "forward-bind-retry-secret", "10.42.0.1", "10.42.0.1", "", "44000-44010", "", "v1", 1, 1, 1, now, now, 1, "10.42.0.9", "[::]", 0).Error; err != nil {
+		t.Fatalf("insert node: %v", err)
+	}
+	nodeID := mustLastInsertID(t, repo, "forward-bind-retry-node")
+
+	if err := repo.DB().Exec(`
+		INSERT INTO chain_tunnel(tunnel_id, chain_type, node_id, port, strategy, inx, protocol)
+		VALUES(?, 1, ?, 44001, 'round', 1, 'tls')
+	`, tunnelID, nodeID).Error; err != nil {
+		t.Fatalf("insert chain_tunnel: %v", err)
+	}
+
+	if err := repo.DB().Exec(`
+		INSERT INTO user_tunnel(id, user_id, tunnel_id, speed_id, num, flow, in_flow, out_flow, flow_reset_time, exp_time, status)
+		VALUES(41, 202, ?, NULL, 999, 99999, 0, 0, 1, 2727251700000, 1)
+	`, tunnelID).Error; err != nil {
+		t.Fatalf("insert user_tunnel: %v", err)
+	}
+
+	createPayload := map[string]interface{}{
+		"name":       "forward-bind-retry-target",
+		"tunnelId":   tunnelID,
+		"remoteAddr": "1.1.1.1:443",
+		"strategy":   "fifo",
+	}
+	createBody, err := json.Marshal(createPayload)
+	if err != nil {
+		t.Fatalf("marshal create payload: %v", err)
+	}
+
+	var mu sync.Mutex
+	counts := map[string]int{}
+	var addServiceAddrs []string
+	triggerConflict := false
+	stopNode := startMockNodeSessionWithCommandRecorder(t, server.URL, "forward-bind-retry-secret", func(cmdType string, data json.RawMessage) (bool, string) {
+		key := strings.ToLower(strings.TrimSpace(cmdType))
+		mu.Lock()
+		counts[key]++
+		attempt := counts[key]
+		if strings.EqualFold(strings.TrimSpace(cmdType), "AddService") || strings.EqualFold(strings.TrimSpace(cmdType), "UpdateService") {
+			var services []map[string]interface{}
+			if err := json.Unmarshal(data, &services); err == nil {
+				for _, svc := range services {
+					if addr, _ := svc["addr"].(string); strings.TrimSpace(addr) != "" {
+						addServiceAddrs = append(addServiceAddrs, addr)
+					}
+				}
+			}
+		}
+		shouldFail := false
+		if triggerConflict {
+			if strings.EqualFold(strings.TrimSpace(cmdType), "UpdateService") && attempt == 1 {
+				shouldFail = true
+			}
+			if strings.EqualFold(strings.TrimSpace(cmdType), "AddService") && attempt == 1 {
+				shouldFail = true
+			}
+		}
+		mu.Unlock()
+		if shouldFail {
+			return true, "listen tcp 10.42.0.9:44001: bind: address already in use"
+		}
+		return false, ""
+	})
+	defer stopNode()
+	waitNodeStatus(t, repo, nodeID, 1)
+
+	createReq := httptest.NewRequest(http.MethodPost, "/api/v1/forward/create", bytes.NewReader(createBody))
+	createReq.Header.Set("Authorization", adminToken)
+	createReq.Header.Set("Content-Type", "application/json")
+	createRes := httptest.NewRecorder()
+	router.ServeHTTP(createRes, createReq)
+	assertCode(t, createRes, 0)
+	mu.Lock()
+	counts = map[string]int{}
+	addServiceAddrs = nil
+	triggerConflict = true
+	mu.Unlock()
+
+	forwardID := mustLastInsertID(t, repo, "forward-bind-retry-target")
+
+	updatePayload := map[string]interface{}{
+		"id":         forwardID,
+		"name":       "forward-bind-retry-target-updated",
+		"tunnelId":   tunnelID,
+		"remoteAddr": "9.9.9.9:8443",
+		"strategy":   "fifo",
+	}
+	updateBody, err := json.Marshal(updatePayload)
+	if err != nil {
+		t.Fatalf("marshal update payload: %v", err)
+	}
+	updateReq := httptest.NewRequest(http.MethodPost, "/api/v1/forward/update", bytes.NewReader(updateBody))
+	updateReq.Header.Set("Authorization", adminToken)
+	updateReq.Header.Set("Content-Type", "application/json")
+	updateRes := httptest.NewRecorder()
+	router.ServeHTTP(updateRes, updateReq)
+	assertCode(t, updateRes, 0)
+
+	mu.Lock()
+	defer mu.Unlock()
+	boundPort := mustQueryInt(t, repo, `SELECT port FROM forward_port WHERE forward_id = ? LIMIT 1`, forwardID)
+	if counts["updateservice"] != 1 {
+		t.Fatalf("expected one UpdateService attempt, got %d (%v)", counts["updateservice"], counts)
+	}
+	if counts["deleteservice"] == 0 {
+		t.Fatalf("expected DeleteService cleanup after address-in-use (%v)", counts)
+	}
+	if counts["addservice"] < 2 {
+		t.Fatalf("expected AddService retry path to run at least twice total, got %d (%v)", counts["addservice"], counts)
+	}
+	foundBindAddr := false
+	for _, addr := range addServiceAddrs {
+		if addr == "10.42.0.9:"+strconv.Itoa(boundPort) {
+			foundBindAddr = true
+			break
+		}
+	}
+	if !foundBindAddr {
+		t.Fatalf("expected forward runtime to keep node listen addr 10.42.0.9:%d, got %v", boundPort, addServiceAddrs)
+	}
+
+	storedRemoteAddr := mustQueryString(t, repo, `SELECT remote_addr FROM forward WHERE id = ?`, forwardID)
+	if storedRemoteAddr != "9.9.9.9:8443" {
+		t.Fatalf("expected remote_addr update to persist, got %q", storedRemoteAddr)
+	}
+}
+
 func jsonNumber(v int64) string {
 	return strconv.FormatInt(v, 10)
 }

go-backend/tests/contract/limiter_sync_failure_contract_test.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"sort"
 	"strings"
 	"sync"
 	"testing"
@@ -538,6 +539,134 @@ func TestBatchAssignInsertRollbackWhenLimiterDispatchFailsContract(t *testing.T)
 	}
 }
 
+func TestTunnelUpdateRecoversFromAddressInUseContract(t *testing.T) {
+	secret := "contract-jwt-secret"
+	router, r := setupContractRouter(t, secret)
+	server := httptest.NewServer(router)
+	defer server.Close()
+
+	adminToken, err := auth.GenerateToken(1, "admin_user", 0, secret)
+	if err != nil {
+		t.Fatalf("generate admin token: %v", err)
+	}
+
+	now := time.Now().UnixMilli()
+	if err := r.DB().Exec(`
+		INSERT INTO tunnel(name, traffic_ratio, type, protocol, flow, created_time, updated_time, status, in_ip, inx)
+		VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`, "tunnel-bind-retry", 1.0, 1, "tls", 99999, now, now, 1, nil, 0).Error; err != nil {
+		t.Fatalf("insert tunnel: %v", err)
+	}
+	tunnelID := mustLastInsertID(t, r, "tunnel-bind-retry")
+
+	if err := r.DB().Exec(`
+		INSERT INTO node(name, secret, server_ip, server_ip_v4, server_ip_v6, port, interface_name, version, http, tls, socks, created_time, updated_time, status, tcp_listen_addr, udp_listen_addr, inx)
+		VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`, "tunnel-bind-entry", "tunnel-bind-entry-secret", "10.41.0.1", "10.41.0.1", "", "43000-43010", "", "v1", 1, 1, 1, now, now, 1, "10.41.0.1", "[::]", 0).Error; err != nil {
+		t.Fatalf("insert entry node: %v", err)
+	}
+	entryNodeID := mustLastInsertID(t, r, "tunnel-bind-entry")
+
+	if err := r.DB().Exec(`
+		INSERT INTO node(name, secret, server_ip, server_ip_v4, server_ip_v6, port, interface_name, version, http, tls, socks, created_time, updated_time, status, tcp_listen_addr, udp_listen_addr, inx)
+		VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`, "tunnel-bind-exit", "tunnel-bind-exit-secret", "10.41.0.2", "10.41.0.2", "", "43100-43110", "eth0", "v1", 1, 1, 1, now, now, 1, "10.41.0.9", "[::]", 0).Error; err != nil {
+		t.Fatalf("insert exit node: %v", err)
+	}
+	exitNodeID := mustLastInsertID(t, r, "tunnel-bind-exit")
+
+	if err := r.DB().Exec(`
+		INSERT INTO chain_tunnel(tunnel_id, chain_type, node_id, port, strategy, inx, protocol)
+		VALUES(?, 1, ?, 43001, 'round', 1, 'tls')
+	`, tunnelID, entryNodeID).Error; err != nil {
+		t.Fatalf("insert entry chain_tunnel: %v", err)
+	}
+	if err := r.DB().Exec(`
+		INSERT INTO chain_tunnel(tunnel_id, chain_type, node_id, port, strategy, inx, protocol, connect_ip)
+		VALUES(?, 3, ?, 43101, 'round', 1, 'tls', ?)
+	`, tunnelID, exitNodeID, "10.41.0.99").Error; err != nil {
+		t.Fatalf("insert exit chain_tunnel: %v", err)
+	}
+
+	var commandMu sync.Mutex
+	commandCounts := map[string]int{}
+	var addServiceAddrs []string
+	stopEntry := startMockNodeSessionWithCommandRecorder(t, server.URL, "tunnel-bind-entry-secret", func(cmdType string, data json.RawMessage) (bool, string) {
+		commandMu.Lock()
+		defer commandMu.Unlock()
+		commandCounts["entry:"+strings.ToLower(strings.TrimSpace(cmdType))]++
+		return false, ""
+	})
+	defer stopEntry()
+	stopExit := startMockNodeSessionWithCommandRecorder(t, server.URL, "tunnel-bind-exit-secret", func(cmdType string, data json.RawMessage) (bool, string) {
+		key := "exit:" + strings.ToLower(strings.TrimSpace(cmdType))
+		commandMu.Lock()
+		commandCounts[key]++
+		attempt := commandCounts[key]
+		if strings.EqualFold(strings.TrimSpace(cmdType), "AddService") {
+			var services []map[string]interface{}
+			if err := json.Unmarshal(data, &services); err == nil {
+				for _, svc := range services {
+					if addr, _ := svc["addr"].(string); strings.TrimSpace(addr) != "" {
+						addServiceAddrs = append(addServiceAddrs, addr)
+					}
+				}
+			}
+		}
+		commandMu.Unlock()
+		if strings.EqualFold(strings.TrimSpace(cmdType), "AddService") && attempt == 1 {
+			return true, "listen tcp 10.41.0.99:43101: bind: address already in use"
+		}
+		return false, ""
+	})
+	defer stopExit()
+	waitNodeStatus(t, r, entryNodeID, 1)
+	waitNodeStatus(t, r, exitNodeID, 1)
+
+	payload := map[string]interface{}{
+		"id":           tunnelID,
+		"name":         "tunnel-bind-retry",
+		"type":         2,
+		"flow":         99999,
+		"trafficRatio": 1.0,
+		"status":       1,
+		"inNodeId": []map[string]interface{}{
+			{"nodeId": entryNodeID, "protocol": "tls", "strategy": "round"},
+		},
+		"chainNodes": []interface{}{},
+		"outNodeId": []map[string]interface{}{
+			{"nodeId": exitNodeID, "protocol": "tls", "strategy": "round", "port": 43101, "connectIp": "10.41.0.99"},
+		},
+	}
+	body, err := json.Marshal(payload)
+	if err != nil {
+		t.Fatalf("marshal payload: %v", err)
+	}
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/tunnel/update", bytes.NewReader(body))
+	req.Header.Set("Authorization", adminToken)
+	req.Header.Set("Content-Type", "application/json")
+	res := httptest.NewRecorder()
+	router.ServeHTTP(res, req)
+	assertCode(t, res, 0)
+
+	commandMu.Lock()
+	defer commandMu.Unlock()
+	if commandCounts["exit:addservice"] != 2 {
+		t.Fatalf("expected exit AddService twice, got %d (%v)", commandCounts["exit:addservice"], sortedCommandCounts(commandCounts))
+	}
+	if commandCounts["exit:deleteservice"] == 0 {
+		t.Fatalf("expected exit DeleteService retry cleanup to run (%v)", sortedCommandCounts(commandCounts))
+	}
+	if len(addServiceAddrs) < 2 {
+		t.Fatalf("expected recorded AddService addresses, got %v", addServiceAddrs)
+	}
+	for _, addr := range addServiceAddrs {
+		if addr != "10.41.0.99:43101" {
+			t.Fatalf("expected connectIp to stay preferred in AddService addr, got %q", addr)
+		}
+	}
+}
+
 func startMockNodeSessionWithCommandFailures(t *testing.T, baseURL string, nodeSecret string, failCommands map[string]string) func() {
 	t.Helper()
 
@@ -633,3 +762,112 @@ func startMockNodeSessionWithCommandFailures(t *testing.T, baseURL string, nodeS
 		})
 	}
 }
+
+func startMockNodeSessionWithCommandRecorder(t *testing.T, baseURL string, nodeSecret string, onCommand func(cmdType string, data json.RawMessage) (bool, string)) func() {
+	t.Helper()
+
+	u, err := url.Parse(baseURL)
+	if err != nil {
+		t.Fatalf("parse provider url: %v", err)
+	}
+	if strings.EqualFold(u.Scheme, "https") {
+		u.Scheme = "wss"
+	} else {
+		u.Scheme = "ws"
+	}
+	u.Path = "/system-info"
+	q := u.Query()
+	q.Set("type", "1")
+	q.Set("secret", nodeSecret)
+	q.Set("version", "v1")
+	q.Set("http", "1")
+	q.Set("tls", "1")
+	q.Set("socks", "1")
+	u.RawQuery = q.Encode()
+
+	conn, _, err := websocket.DefaultDialer.Dial(u.String(), nil)
+	if err != nil {
+		t.Fatalf("dial mock node websocket: %v", err)
+	}
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for {
+			_, raw, readErr := conn.ReadMessage()
+			if readErr != nil {
+				return
+			}
+
+			plain := raw
+			var wrap struct {
+				Encrypted bool   `json:"encrypted"`
+				Data      string `json:"data"`
+			}
+			if err := json.Unmarshal(raw, &wrap); err == nil && wrap.Encrypted && strings.TrimSpace(wrap.Data) != "" {
+				crypto, cryptoErr := security.NewAESCrypto(nodeSecret)
+				if cryptoErr == nil {
+					if dec, decErr := crypto.Decrypt(wrap.Data); decErr == nil {
+						plain = []byte(dec)
+					}
+				}
+			}
+
+			var cmd struct {
+				Type      string          `json:"type"`
+				RequestID string          `json:"requestId"`
+				Data      json.RawMessage `json:"data"`
+			}
+			if err := json.Unmarshal(plain, &cmd); err != nil {
+				continue
+			}
+			if strings.TrimSpace(cmd.RequestID) == "" {
+				continue
+			}
+
+			shouldFail := false
+			failMsg := ""
+			if onCommand != nil {
+				shouldFail, failMsg = onCommand(strings.TrimSpace(cmd.Type), cmd.Data)
+			}
+
+			respType := fmt.Sprintf("%sResponse", cmd.Type)
+			respPayload := map[string]interface{}{
+				"type":      respType,
+				"success":   !shouldFail,
+				"message":   "OK",
+				"requestId": cmd.RequestID,
+			}
+			if shouldFail {
+				if strings.TrimSpace(failMsg) == "" {
+					failMsg = "mock command failed"
+				}
+				respPayload["message"] = failMsg
+			}
+
+			respBytes, err := json.Marshal(respPayload)
+			if err != nil {
+				continue
+			}
+			_ = conn.WriteMessage(websocket.TextMessage, respBytes)
+		}
+	}()
+
+	var stopOnce sync.Once
+	return func() {
+		stopOnce.Do(func() {
+			_ = conn.Close()
+			wg.Wait()
+		})
+	}
+}
+
+func sortedCommandCounts(counts map[string]int) []string {
+	items := make([]string, 0, len(counts))
+	for key, value := range counts {
+		items = append(items, fmt.Sprintf("%s=%d", key, value))
+	}
+	sort.Strings(items)
+	return items
+}

plans/016-tunnel-runtime-bind-conflict-retry.md

@@ -0,0 +1,27 @@
+# 016 Tunnel Runtime Bind Conflict Retry
+
+## Checklist
+
+- [x] Confirm tunnel `connectIp` precedence remains `connectIp > node tcp_listen_addr` for runtime service listen address.
+- [x] Add tunnel runtime `address already in use` recovery that deletes the stale service and retries `AddService`.
+- [x] Keep non-bind failures unchanged and avoid altering tunnel chain apply semantics.
+- [x] Add regression tests for tunnel service address precedence and bind-conflict retry behavior.
+- [x] Run focused backend handler tests and record the result.
+- [ ] Add a contract test that simulates node-side `address already in use` during tunnel update and verifies retry success.
+- [ ] Investigate whether forward update `address already in use` reports are only tunnel-redeploy linkage or also an independent forward path.
+- [x] Add a contract test that simulates node-side `address already in use` during tunnel update and verifies retry success.
+- [x] Investigate whether forward update `address already in use` reports are only tunnel-redeploy linkage or also an independent forward path.
+
+## Test Record
+
+- Command: `cd go-backend && go test ./internal/http/handler/...`
+- Result: passed.
+- Command: `cd go-backend && go test ./tests/contract/... -run 'TestTunnelUpdateRecoversFromAddressInUseContract|TestForwardCreateRollbackWhenServiceDispatchReturnsAddressInUseContract|TestForwardUpdateIgnoresDeletedSpeedLimitContract'`
+- Result: passed.
+- Command: `cd go-backend && go test ./tests/contract/... -run 'TestForwardUpdateRecoversFromAddressInUseContract|TestTunnelUpdateRecoversFromAddressInUseContract'`
+- Result: passed.
+
+## Investigation Note
+
+- Forward update still has its own independent `address already in use` recovery path in `syncForwardServicesWithWarnings` / `rebindForwardServiceOnSelfOccupiedPort`; tunnel update linkage is not the only possible source of the symptom.
+- Tunnel update also triggers downstream forward `UpdateService` for bound forwards, so users can still observe the same error around a tunnel edit even when the failing runtime is on the tunnel side.