ax(node): rename Transport.mu to mutex (AX Principle 1)

Abbreviated field name `mu` is ambiguous — rename to `mutex` to satisfy
AX-025 §1 (predictable names over short names).

Co-Authored-By: Charon <charon@lethean.io>

pkg/node/transport.go

@@ -109,7 +109,7 @@ type Transport struct {
 	registry     *PeerRegistry
 	handler      MessageHandler
 	dedup        *MessageDeduplicator // Message deduplication
-	mu           sync.RWMutex
+	mutex        sync.RWMutex
 	ctx          context.Context
 	cancel       context.CancelFunc
 	waitGroup    sync.WaitGroup
@@ -277,11 +277,11 @@ func (t *Transport) Stop() error {
 	t.cancel()
 
 	// Gracefully close all connections with shutdown message
-	t.mu.Lock()
+	t.mutex.Lock()
 	for _, pc := range t.conns {
 		pc.GracefulClose("server shutdown", DisconnectShutdown)
 	}
-	t.mu.Unlock()
+	t.mutex.Unlock()
 
 	// Shutdown HTTP server if it was started
 	if t.server != nil {
@@ -300,8 +300,8 @@ func (t *Transport) Stop() error {
 // OnMessage sets the handler for incoming messages.
 // Must be called before Start() to avoid races.
 func (t *Transport) OnMessage(handler MessageHandler) {
-	t.mu.Lock()
-	defer t.mu.Unlock()
+	t.mutex.Lock()
+	defer t.mutex.Unlock()
 	t.handler = handler
 }
 
@@ -339,9 +339,9 @@ func (t *Transport) Connect(peer *Peer) (*PeerConnection, error) {
 	}
 
 	// Store connection using the real peer ID from handshake
-	t.mu.Lock()
+	t.mutex.Lock()
 	t.conns[pc.Peer.ID] = pc
-	t.mu.Unlock()
+	t.mutex.Unlock()
 
 	logging.Debug("connected to peer", logging.Fields{"peer_id": pc.Peer.ID, "secret_len": len(pc.SharedSecret)})
 
@@ -363,9 +363,9 @@ func (t *Transport) Connect(peer *Peer) (*PeerConnection, error) {
 
 // if err := transport.Send(peer.ID, msg); err != nil { return err }
 func (t *Transport) Send(peerID string, msg *Message) error {
-	t.mu.RLock()
+	t.mutex.RLock()
 	pc, exists := t.conns[peerID]
-	t.mu.RUnlock()
+	t.mutex.RUnlock()
 
 	if !exists {
 		return fmt.Errorf("peer %s not connected", peerID)
@@ -377,7 +377,7 @@ func (t *Transport) Send(peerID string, msg *Message) error {
 // Broadcast sends a message to all connected peers except the sender.
 // The sender is identified by msg.From and excluded to prevent echo.
 func (t *Transport) Broadcast(msg *Message) error {
-	t.mu.RLock()
+	t.mutex.RLock()
 	conns := make([]*PeerConnection, 0, len(t.conns))
 	for _, pc := range t.conns {
 		// Exclude sender from broadcast to prevent echo (P2P-MED-6)
@@ -386,7 +386,7 @@ func (t *Transport) Broadcast(msg *Message) error {
 		}
 		conns = append(conns, pc)
 	}
-	t.mu.RUnlock()
+	t.mutex.RUnlock()
 
 	var lastErr error
 	for _, pc := range conns {
@@ -399,17 +399,17 @@ func (t *Transport) Broadcast(msg *Message) error {
 
 // GetConnection returns an active connection to a peer.
 func (t *Transport) GetConnection(peerID string) *PeerConnection {
-	t.mu.RLock()
-	defer t.mu.RUnlock()
+	t.mutex.RLock()
+	defer t.mutex.RUnlock()
 	return t.conns[peerID]
 }
 
 // handleWSUpgrade handles incoming WebSocket connections.
 func (t *Transport) handleWSUpgrade(w http.ResponseWriter, r *http.Request) {
 	// Enforce MaxConns limit (including pending connections during handshake)
-	t.mu.RLock()
+	t.mutex.RLock()
 	currentConns := len(t.conns)
-	t.mu.RUnlock()
+	t.mutex.RUnlock()
 	pendingConns := int(t.pendingConns.Load())
 
 	totalConns := currentConns + pendingConns
@@ -583,9 +583,9 @@ func (t *Transport) handleWSUpgrade(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Store connection
-	t.mu.Lock()
+	t.mutex.Lock()
 	t.conns[peer.ID] = pc
-	t.mu.Unlock()
+	t.mutex.Unlock()
 
 	// Update registry
 	t.registry.SetConnected(peer.ID, true)
@@ -764,9 +764,9 @@ func (t *Transport) readLoop(pc *PeerConnection) {
 		}
 
 		// Dispatch to handler (read handler under lock to avoid race)
-		t.mu.RLock()
+		t.mutex.RLock()
 		handler := t.handler
-		t.mu.RUnlock()
+		t.mutex.RUnlock()
 		if handler != nil {
 			handler(pc, msg)
 		}
@@ -810,9 +810,9 @@ func (t *Transport) keepalive(pc *PeerConnection) {
 
 // removeConnection removes and cleans up a connection.
 func (t *Transport) removeConnection(pc *PeerConnection) {
-	t.mu.Lock()
+	t.mutex.Lock()
 	delete(t.conns, pc.Peer.ID)
-	t.mu.Unlock()
+	t.mutex.Unlock()
 
 	t.registry.SetConnected(pc.Peer.ID, false)
 	pc.Close()
@@ -931,7 +931,7 @@ func (t *Transport) decryptMessage(data []byte, sharedSecret []byte) (*Message,
 // n := transport.ConnectedPeers()
 // if n == 0 { return ErrNoPeers }
 func (t *Transport) ConnectedPeers() int {
-	t.mu.RLock()
-	defer t.mu.RUnlock()
+	t.mutex.RLock()
+	defer t.mutex.RUnlock()
 	return len(t.conns)
 }