fix: terminate background processes on app quit

Adds terminateAll() to BackgroundProcessManager and hooks it into
Electron's before-quit event, preventing orphaned processes when
mux exits normally. Crash recovery (orphans from SIGKILL) remains
out of scope.

Author: ethanndickson

src/desktop/main.ts

@@ -540,6 +540,18 @@ if (gotTheLock) {
     }
   });
 
+  // Track if we're already quitting to avoid re-entrancy
+  let isQuitting = false;
+  app.on("before-quit", (event) => {
+    if (ipcMain && !isQuitting) {
+      isQuitting = true;
+      event.preventDefault();
+      ipcMain.terminateAllBackgroundProcesses().finally(() => {
+        app.exit(0);
+      });
+    }
+  });
+
   app.on("activate", () => {
     // Only create window if app is ready and no window exists
     // This prevents "Cannot create BrowserWindow before app is ready" error

src/node/services/backgroundProcessManager.ts

@@ -194,4 +194,16 @@ export class BackgroundProcessManager {
 
     log.debug(`Cleaned up ${matching.length} process(es) for workspace ${workspaceId}`);
   }
+
+  /**
+   * Terminate all background processes across all workspaces.
+   * Called on app shutdown to prevent orphaned processes.
+   */
+  async terminateAll(): Promise<void> {
+    log.debug(`BackgroundProcessManager.terminateAll() called`);
+    const allProcesses = Array.from(this.processes.values());
+    await Promise.all(allProcesses.map((p) => this.terminate(p.id)));
+    this.processes.clear();
+    log.debug(`Terminated ${allProcesses.length} background process(es)`);
+  }
 }

src/node/services/ipcMain.ts

@@ -112,6 +112,13 @@ export class IpcMain {
     await this.extensionMetadata.initialize();
   }
 
+  /**
+   * Terminate all background processes. Called on app shutdown.
+   */
+  async terminateAllBackgroundProcesses(): Promise<void> {
+    await this.backgroundProcessManager.terminateAll();
+  }
+
   /**
    * Configure a picker used to select project directories (desktop mode only).
    * Server mode does not provide a native directory picker.