fix: improve extension runtime safety, HTTP response URL, SongLink parsing, and recommended service for extensions

- Add 'url' field (final URL after redirects) to all extension HTTP responses and fix fetch polyfill to return final URL instead of original request URL
- Fix RunWithTimeout race condition: increase force-timeout from 1s to 60s to prevent concurrent VM access crashes, add nil guards
- Use lockReadyVM() for thread-safe VM access in GetPlaylistWithExtensionJSON and InvokeAction
- Handle mixed JSON types (string, null, array) in SongLink resolve API SongUrls field
- Fix recommended download service not showing for extension-based searches in download picker

.gitignore

@@ -77,6 +77,7 @@ flutter_*.log
 # Development tools
 tool/
 .claude/settings.local.json
+.playwright-mcp/
 
 # FVM Version Cache
 .fvm/

go_backend/exports.go

@@ -3212,8 +3212,15 @@ func GetPlaylistWithExtensionJSON(extensionID, playlistID string) (string, error
 	if !ext.Manifest.IsMetadataProvider() {
 		return "", fmt.Errorf("extension '%s' is not a metadata provider", extensionID)
 	}
+	if !ext.Enabled {
+		return "", fmt.Errorf("extension '%s' is disabled", extensionID)
+	}
 
-	provider := NewExtensionProviderWrapper(ext)
+	vm, err := ext.lockReadyVM()
+	if err != nil {
+		return "", err
+	}
+	defer ext.VMMu.Unlock()
 
 	script := fmt.Sprintf(`
 		(function() {
@@ -3227,7 +3234,7 @@ func GetPlaylistWithExtensionJSON(extensionID, playlistID string) (string, error
 		})()
 	`, playlistID, playlistID)
 
-	result, err := RunWithTimeoutAndRecover(provider.vm, script, DefaultJSTimeout)
+	result, err := RunWithTimeoutAndRecover(vm, script, DefaultJSTimeout)
 	if err != nil {
 		return "", fmt.Errorf("getPlaylist failed: %w", err)
 	}

go_backend/extension_manager.go

@@ -1044,13 +1044,14 @@ func (m *ExtensionManager) InvokeAction(extensionID string, actionName string) (
 		return nil, fmt.Errorf("extension not found: %s", extensionID)
 	}
 
-	if err := ext.ensureRuntimeReady(); err != nil {
-		return nil, err
-	}
-
 	if !ext.Enabled {
 		return nil, fmt.Errorf("extension is disabled")
 	}
+	vm, err := ext.lockReadyVM()
+	if err != nil {
+		return nil, err
+	}
+	defer ext.VMMu.Unlock()
 
 	script := fmt.Sprintf(`
 		(function() {
@@ -1070,7 +1071,7 @@ func (m *ExtensionManager) InvokeAction(extensionID string, actionName string) (
 		})()
 	`, actionName, actionName, actionName)
 
-	result, err := RunWithTimeoutAndRecover(ext.VM, script, DefaultJSTimeout)
+	result, err := RunWithTimeoutAndRecover(vm, script, DefaultJSTimeout)
 	if err != nil {
 		GoLog("[Extension] InvokeAction error for %s.%s: %v\n", extensionID, actionName, err)
 		return nil, fmt.Errorf("action failed: %v", err)

go_backend/extension_runtime_http.go

@@ -118,6 +118,7 @@ func (r *ExtensionRuntime) httpGet(call goja.FunctionCall) goja.Value {
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})
@@ -214,6 +215,7 @@ func (r *ExtensionRuntime) httpPost(call goja.FunctionCall) goja.Value {
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})
@@ -322,6 +324,7 @@ func (r *ExtensionRuntime) httpRequest(call goja.FunctionCall) goja.Value {
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})
@@ -446,6 +449,7 @@ func (r *ExtensionRuntime) httpMethodShortcut(method string, call goja.FunctionC
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})

go_backend/extension_runtime_polyfills.go

@@ -105,7 +105,7 @@ func (r *ExtensionRuntime) fetchPolyfill(call goja.FunctionCall) goja.Value {
 	responseObj.Set("status", resp.StatusCode)
 	responseObj.Set("statusText", http.StatusText(resp.StatusCode))
 	responseObj.Set("headers", respHeaders)
-	responseObj.Set("url", urlStr)
+	responseObj.Set("url", resp.Request.URL.String())
 
 	bodyString := string(body)
 

go_backend/extension_timeout.go

@@ -20,6 +20,10 @@ func (e *JSExecutionError) Error() string {
 }
 
 func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goja.Value, error) {
+	if vm == nil {
+		return nil, fmt.Errorf("extension runtime unavailable")
+	}
+
 	if timeout <= 0 {
 		timeout = DefaultJSTimeout
 	}
@@ -69,6 +73,11 @@ func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goj
 
 		vm.Interrupt("execution timeout")
 
+		// MUST wait for the goroutine to finish before returning.
+		// The Goja VM is NOT thread-safe — if we return while the goroutine
+		// is still executing JS (e.g. blocked on an HTTP call), the next
+		// caller will access the VM concurrently and crash with a nil
+		// pointer dereference.
 		select {
 		case res := <-resultCh:
 			if res.err != nil {
@@ -78,7 +87,10 @@ func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goj
 				Message:   "execution timeout exceeded",
 				IsTimeout: true,
 			}
-		case <-time.After(1 * time.Second):
+		case <-time.After(60 * time.Second):
+			// Goroutine is truly stuck (e.g. HTTP read with no timeout).
+			// Log a warning — the VM should NOT be reused after this.
+			GoLog("[ExtensionRuntime] WARNING: JS goroutine did not exit within 60s after interrupt, VM may be unsafe\n")
 			return nil, &JSExecutionError{
 				Message:   "execution timeout exceeded (force)",
 				IsTimeout: true,
@@ -93,7 +105,9 @@ func RunWithTimeoutAndRecover(vm *goja.Runtime, script string, timeout time.Dura
 	result, err := RunWithTimeout(vm, script, timeout)
 
 	// Clear any interrupt state so VM can be reused
-	vm.ClearInterrupt()
+	if vm != nil {
+		vm.ClearInterrupt()
+	}
 
 	return result, err
 }

go_backend/songlink.go

@@ -164,9 +164,9 @@ func (s *SongLinkClient) doResolveRequest(payload []byte) (map[string]songLinkPl
 	}
 
 	var resolveResp struct {
-		Success  bool              `json:"success"`
-		ISRC     string            `json:"isrc"`
-		SongUrls map[string]string `json:"songUrls"`
+		Success  bool                           `json:"success"`
+		ISRC     string                         `json:"isrc"`
+		SongUrls map[string]json.RawMessage     `json:"songUrls"`
 	}
 	if err := json.Unmarshal(body, &resolveResp); err != nil {
 		return nil, fmt.Errorf("failed to decode resolve response: %w", err)
@@ -189,8 +189,12 @@ func (s *SongLinkClient) doResolveRequest(payload []byte) (map[string]songLinkPl
 
 	links := make(map[string]songLinkPlatformLink)
 	for resolveKey, platformKey := range keyMap {
-		if u, ok := resolveResp.SongUrls[resolveKey]; ok && strings.TrimSpace(u) != "" {
-			links[platformKey] = songLinkPlatformLink{URL: strings.TrimSpace(u)}
+		rawValue, ok := resolveResp.SongUrls[resolveKey]
+		if !ok {
+			continue
+		}
+		if u := extractResolveURLValue(rawValue); u != "" {
+			links[platformKey] = songLinkPlatformLink{URL: u}
 		}
 	}
 
@@ -201,6 +205,29 @@ func (s *SongLinkClient) doResolveRequest(payload []byte) (map[string]songLinkPl
 	return links, nil
 }
 
+func extractResolveURLValue(raw json.RawMessage) string {
+	trimmed := bytes.TrimSpace(raw)
+	if len(trimmed) == 0 || bytes.Equal(trimmed, []byte("null")) {
+		return ""
+	}
+
+	var direct string
+	if err := json.Unmarshal(trimmed, &direct); err == nil {
+		return strings.TrimSpace(direct)
+	}
+
+	var list []string
+	if err := json.Unmarshal(trimmed, &list); err == nil {
+		for _, candidate := range list {
+			if cleaned := strings.TrimSpace(candidate); cleaned != "" {
+				return cleaned
+			}
+		}
+	}
+
+	return ""
+}
+
 // songLinkByTargetURL calls the SongLink API with a target URL (for non-Spotify URLs).
 func (s *SongLinkClient) songLinkByTargetURL(targetURL string) (map[string]songLinkPlatformLink, error) {
 	songLinkRateLimiter.WaitForSlot()

go_backend/songlink_test.go

@@ -114,6 +114,47 @@ func TestCheckTrackAvailabilityFromSpotifyResolveAPIFailure(t *testing.T) {
 	}
 }
 
+func TestCheckTrackAvailabilityFromSpotifyViaResolveAPIMixedSongURLShapes(t *testing.T) {
+	origRetryConfig := songLinkRetryConfig
+	defer func() { songLinkRetryConfig = origRetryConfig }()
+
+	client := &SongLinkClient{
+		client: &http.Client{
+			Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+				if req.URL.Host == "api.zarz.moe" && req.URL.Path == "/v1/resolve" && req.Method == "POST" {
+					body := `{"success":true,"isrc":"TCAHA2367688","songUrls":{"Spotify":"https://open.spotify.com/track/5glgyj6zH0irbNGfukHacv","Deezer":"https://www.deezer.com/track/2248583177","Tidal":"https://tidal.com/browse/track/290565315","AppleMusic":"https://geo.music.apple.com/us/album/example?i=1","YouTubeMusic":null,"YouTube":"https://www.youtube.com/watch?v=wD_e59XUNdQ","AmazonMusic":"https://music.amazon.com/tracks/B0C35TG38Y/?ref=dm_ff_amazonmusic_3p","Beatport":null,"BeatSource":null,"SoundCloud":null,"Qobuz":null,"Other":[]}}`
+					return &http.Response{
+						StatusCode: 200,
+						Header:     make(http.Header),
+						Body:       io.NopCloser(strings.NewReader(body)),
+						Request:    req,
+					}, nil
+				}
+				t.Fatalf("unexpected request: %s %s", req.Method, req.URL.String())
+				return nil, nil
+			}),
+		},
+	}
+
+	availability, err := client.CheckTrackAvailability("5glgyj6zH0irbNGfukHacv", "")
+	if err != nil {
+		t.Fatalf("CheckTrackAvailability() error = %v", err)
+	}
+
+	if availability.SpotifyID != "5glgyj6zH0irbNGfukHacv" {
+		t.Fatalf("SpotifyID = %q, want %q", availability.SpotifyID, "5glgyj6zH0irbNGfukHacv")
+	}
+	if !availability.Deezer || availability.DeezerID != "2248583177" {
+		t.Fatalf("Deezer availability = %+v, want DeezerID 2248583177", availability)
+	}
+	if !availability.Tidal || availability.TidalID != "290565315" {
+		t.Fatalf("Tidal availability = %+v, want TidalID 290565315", availability)
+	}
+	if availability.Qobuz {
+		t.Fatalf("Qobuz should remain false when resolve response contains null, got %+v", availability)
+	}
+}
+
 func TestCheckAvailabilityFromDeezerUsesSongLink(t *testing.T) {
 	origRetryConfig := songLinkRetryConfig
 	songLinkRetryConfig = func() RetryConfig {

lib/screens/home_tab.dart

@@ -757,7 +757,8 @@ class _HomeTabState extends ConsumerState<HomeTab>
           trackName: track.name,
           artistName: track.artistName,
           coverUrl: track.coverUrl,
-          recommendedService: trackState.searchSource,
+          recommendedService:
+              trackState.searchExtensionId ?? trackState.searchSource,
           onSelect: (quality, service) {
             ref
                 .read(downloadQueueProvider.notifier)