fix: eliminate screen share audio feedback loop + upgrade Electron 33→40

Screen sharing with audio captured the app's own voice playback, causing
users to hear themselves echoed back. Fixed via two layers:

- Add restrictOwnAudio constraint (Chrome 141+/Chromium 144) to exclude
  the app's own audio from system audio capture
- Add shareAudio toggle so users can disable system audio entirely
- Remove outdated macOS audio block (now supported via ScreenCaptureKit)
- Upgrade Electron 33→40 (Chromium 130→144) so restrictOwnAudio works
  natively in the desktop app
- Add NSAudioCaptureUsageDescription for macOS 14.2+ audio capture
- Add GTK 3 fallback for Linux GNOME compatibility (Electron 36+)

packages/desktop/electron-builder.yml

@@ -17,6 +17,9 @@ protocols:
       - backspace
 mac:
   category: public.app-category.social-networking
+  minimumSystemVersion: "12.0"
+  extendInfo:
+    NSAudioCaptureUsageDescription: "Backspace needs access to system audio to share sound during screen sharing."
   target:
     - dmg
     - zip

packages/desktop/package.json

@@ -20,7 +20,7 @@
     "electron-updater": "^6.3.0"
   },
   "devDependencies": {
-    "electron": "^33.2.0",
+    "electron": "^40.0.0",
     "electron-builder": "^25.1.8",
     "typescript": "^5.7.2"
   }

packages/desktop/src/main.ts

@@ -432,7 +432,7 @@ function registerIpcHandlers(): void {
   });
 
   // Screen share picker coordination (used by setDisplayMediaRequestHandler)
-  ipcMain.on('screen-share-selected', (_event, sourceId: string | null) => {
+  ipcMain.on('screen-share-selected', (_event, _sourceId: string | null, _shareAudio?: boolean) => {
     // Handled via ipcMain.once in the display media handler — this is just
     // a safety net to prevent unhandled-message warnings
   });
@@ -487,6 +487,12 @@ function handleDeepLink(url: string): void {
   }
 }
 
+// Electron 36+ defaults to GTK 4 on GNOME, which crashes if GTK 2/3
+// libraries are loaded in the same process. Force GTK 3 for compatibility.
+if (process.platform === 'linux') {
+  app.commandLine.appendSwitch('gtk-version', '3');
+}
+
 // Set as default protocol handler
 app.setAsDefaultProtocolClient('backspace');
 
@@ -621,12 +627,12 @@ if (!gotTheLock) {
         // Send sources to renderer, wait for user selection
         mainWindow?.webContents.send('screen-share-sources', serialized);
 
-        const sourceId = await new Promise<string | null>((resolve) => {
-          ipcMain.once('screen-share-selected', (_event, id: string | null) => {
-            resolve(id);
+        const { sourceId, shareAudio } = await new Promise<{ sourceId: string | null; shareAudio: boolean }>((resolve) => {
+          ipcMain.once('screen-share-selected', (_event, id: string | null, wantAudio?: boolean) => {
+            resolve({ sourceId: id, shareAudio: wantAudio ?? true });
           });
         });
-        console.log('[Main:ScreenShare] User selected:', sourceId);
+        console.log('[Main:ScreenShare] User selected:', sourceId, 'audio:', shareAudio);
 
         if (!sourceId) {
           // @ts-ignore — deny the request without crashing
@@ -642,12 +648,9 @@ if (!gotTheLock) {
         }
 
         // Provide the selected source — Electron creates the MediaStream
-        // Enable system audio loopback on Windows/Linux (macOS blocks at OS level)
-        if (process.platform === 'darwin') {
-          callback({ video: selected });
-        } else {
-          callback({ video: selected, audio: 'loopback' });
-        }
+        // System audio loopback: Windows/Linux native, macOS 13+ via ScreenCaptureKit
+        // Controlled by user's shareAudio preference from the picker UI
+        callback({ video: selected, ...(shareAudio ? { audio: 'loopback' } : {}) });
       } catch (err) {
         console.error('[Main:ScreenShare] Handler error:', err);
         // @ts-ignore — deny the request without crashing

packages/desktop/src/preload.ts

@@ -54,8 +54,8 @@ contextBridge.exposeInMainWorld('backspace', {
   onScreenShareSources: (callback: (sources: unknown[]) => void) => {
     ipcRenderer.on('screen-share-sources', (_event, sources) => callback(sources));
   },
-  selectScreenSource: (sourceId: string | null) => {
-    ipcRenderer.send('screen-share-selected', sourceId);
+  selectScreenSource: (sourceId: string | null, shareAudio?: boolean) => {
+    ipcRenderer.send('screen-share-selected', sourceId, shareAudio ?? true);
   },
 
   // Instance URL management