fix(tsconnect/wasm): normalise ":port" listen addr to "0.0.0.0:port"

netstack.ListenTCP requires a full host:port address; callers passing
the standard net.Listen form (":0" for any-interface ephemeral port)
would get ParseAddrPort error. Prepend "0.0.0.0" when the address
starts with ":" so the API matches Go's net.Listen behaviour.

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

cmd/tsconnect/wasm/wasm_js.go

@@ -873,6 +873,11 @@ 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) {