fix(tsconnect/wasm): nil-check lb and ln in shutdown() before use

lb and ln are only initialised during run(); calling shutdown() before
run() panics on nil. Guard both fields before dereferencing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/tsconnect/wasm/wasm_js.go

@@ -637,8 +637,12 @@ func (i *jsIPN) logout() {
 func (i *jsIPN) shutdown() js.Value {
 	return makePromise(func() (any, error) {
 		i.shutdownOnce.Do(func() {
-			i.lb.Shutdown()
-			i.ln.Close()
+			if i.lb != nil {
+				i.lb.Shutdown()
+			}
+			if i.ln != nil {
+				i.ln.Close()
+			}
 			close(i.shutdownCh)
 		})
 		return nil, nil
@@ -873,6 +877,11 @@ func (i *jsIPN) listen(network, addr string) js.Value {
 			if n == "tcp" {
 				n = "tcp4"
 			}
+			// netstack.ListenTCP requires a full host:port; normalise the
+			// standard net.Listen form ":port" that omits the host.
+			if strings.HasPrefix(addr, ":") {
+				addr = "0.0.0.0" + addr
+			}
 			ln, err := i.ns.ListenTCP(n, addr)
 			if err != nil {
 				return nil, err

safesocket/safesocket_js.go

@@ -5,15 +5,22 @@ package safesocket
 
 import (
 	"context"
+	"fmt"
 	"net"
+	"sync/atomic"
 
 	"github.com/akutz/memconn"
 )
 
 const memName = "Tailscale-IPN"
 
+// memSeq ensures each IPN instance in the same WASM process gets a distinct
+// memconn address, so concurrent instances do not conflict on the registry.
+var memSeq atomic.Int64
+
 func listen(path string) (net.Listener, error) {
-	return memconn.Listen("memu", memName)
+	name := fmt.Sprintf("%s-%d", memName, memSeq.Add(1))
+	return memconn.Listen("memu", name)
 }
 
 func connect(ctx context.Context, _ string) (net.Conn, error) {