Keep desktop browser tabs stable across focus and automation (#2907)

* fix(desktop): preserve browser tabs across focus changes

Electron can replace a guest WebContents when a webview is reparented, which reloads the page and can race automation against a destroyed target. Keep each browser guest on one permanent paintable surface and make user and agent resizing share one canonical viewport.

* fix(desktop): recover browser surfaces after lifecycle changes

* fix(desktop): preserve resident browser lifecycle state

* fix(desktop): seed inactive browser viewport

packages/desktop/src/features/browser-automation/ipc.ts

@@ -74,6 +74,7 @@ interface WebContentsDebugger {
     event: "message",
     listener: (event: unknown, method: string, params?: Record<string, unknown>) => void,
   ): void;
+  on?(event: "detach", listener: () => void): void;
 }
 
 interface ConsoleMessageEmitter {
@@ -188,6 +189,7 @@ function getDialogMonitor(
 class DialogMonitor {
   private enabled = false;
   private listenerRegistered = false;
+  private detachGeneration = 0;
   private readonly activeCollectors: DialogCollector[] = [];
 
   public constructor(
@@ -200,10 +202,14 @@ class DialogMonitor {
     task: () => Promise<T>,
   ): Promise<{ result: T; dialogs: BrowserAutomationDialogEvent[] }> {
     const collector: DialogCollector = { dialogs: [] };
+    const setupDetachGeneration = this.detachGeneration;
     try {
       await this.enable();
       await this.installPromptShim();
     } catch (error) {
+      if (this.contents.isDestroyed() || this.detachGeneration !== setupDetachGeneration) {
+        throw error;
+      }
       console.warn("[browser-automation] Dialog capture unavailable; running command without it", {
         contentsId: this.contentsId,
         error,
@@ -244,6 +250,10 @@ class DialogMonitor {
         }
         void this.handleOpening(params ?? {});
       });
+      this.contents.debugger.on("detach", () => {
+        this.enabled = false;
+        this.detachGeneration += 1;
+      });
     }
     await this.sendDebugCommand("Page.enable");
     this.enabled = true;