fix(tsconnect): address bridge review findings

Co-Authored-By: gpt-5.6-sol <noreply@openai.com>

cmd/tsconnect/wasm/taildrop.go

@@ -246,13 +246,16 @@ func wireTaildropFileOps(lb *ipnlocal.LocalBackend, jsObj js.Value) {
 // ReadableStreamDefaultReader. Each Read call awaits one reader.read() Promise,
 // using the channel+FuncOf pattern so Go blocks until JS delivers the chunk.
 type jsStreamReader struct {
-	mu     sync.Mutex
-	reader js.Value
-	buf    []byte
-	done   bool
-	err    error
+	mu                sync.Mutex
+	reader            js.Value
+	buf               []byte
+	done              bool
+	err               error
+	testCancelTimeout time.Duration
 }
 
+const jsStreamCancelTimeout = time.Second
+
 func (r *jsStreamReader) Read(p []byte) (int, error) {
 	r.mu.Lock()
 	if r.err != nil {
@@ -386,8 +389,19 @@ func (r *jsStreamReader) Close() error {
 	if _, err := callJSMethod(promise, "then", resolveFn, rejectFn); err != nil {
 		return r.setError(err)
 	}
-	if err := <-resultCh; err != nil {
-		return r.setError(err)
+	timeout := jsStreamCancelTimeout
+	if r.testCancelTimeout > 0 {
+		timeout = r.testCancelTimeout
+	}
+	timer := time.NewTimer(timeout)
+	defer timer.Stop()
+	select {
+	case err := <-resultCh:
+		if err != nil {
+			return r.setError(err)
+		}
+	case <-timer.C:
+		return r.setError(errors.New("JavaScript stream cancel timed out"))
 	}
 	r.mu.Lock()
 	r.done = true