[Bug]: A browser tab goes blank white after the tab list reloads in a new order #13798

Before submitting

• I searched existing issues and did not find a duplicate. [Bug]: Leaving a thread detaches its browser preview and can leave automation unusable #6355 has the same trigger (leaving a thread and coming back), but there preview_status still reports the tab as usable and snapshots fail with UnknownVizError. Here the tab's page is destroyed and preview_status reports it unavailable. The two may be related.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. In a desktop thread, have the agent open a tab with preview_open for https://example.com (tab A), then another with preview_open, reuseExistingTab: false, for https://example.org (tab B).
2. Have the agent navigate tab A to https://example.net, so tab A is now the most recently updated tab.
3. Switch to another thread, come back, and open the browser panel.
4. Look at tab A, and have the agent call preview_status and preview_navigate on it.

Expected behavior

Both tabs keep their pages, and the agent can keep using tab A.

Actual behavior

Tab A shows a blank white page. preview_status returns available: false and url: null, and preview_navigate or preview_snapshot on it waits the full 15 seconds and fails with PreviewAutomationTimeoutError. Tab B still works.

preview.list returns tabs sorted by updatedAt, and reconcilePreviewServerSessions rebuilds the session map in that order. ElectronBrowserHost renders one keyed <webview> per tab in the same order, so when the order changes React moves a <webview> element. Electron destroys a webview's guest when its element leaves the DOM, and no new guest attaches when it is inserted again. The element then shows only its white background, while the desktop still has the tab registered to the destroyed WebContents.

A standalone Electron 44.4.2 script shows the same result: moving a <webview> with insertBefore fires destroyed for its WebContents, did-attach does not fire again, and executeJavaScript fails with Invalid guestInstanceId.

Impact

Major degradation or frequent failure

Version or commit

A build of main at 5d707bb. The affected code is unchanged on main at 2679d27.

Environment

Windows 11 x64, T3 Code desktop app (Electron 44.4.2), Claude Code provider. The move behavior comes from Electron's <webview> element, so other platforms are likely affected too. I tested only Windows.

Workaround

Close the blank tab and open a new one.