Pop the preview browser out into its own window (multi-monitor)

[brunodubcosta]

Problem

On desktop, "Open separate preview window" opens a view-only picture-in-picture window. It shows screenshots of the tab at about 12 fps, and you can't click or type in it. If you work across several monitors, there's no way to put a browser you can actually use on another screen while the chat stays on the main one.

Proposal

Add Pop out to window for a browser tab. It opens a second app window that renders only that tab's toolbar and a working webview. The panel in the main window shows a placeholder with Bring back. Closing the pop-out window also brings the tab back.

• The tab keeps its identity, so agent control, recording, annotations and the profile partition (logins and cookies) keep working.
• The main process owns the list of popped-out tabs and sends it to every window, so a tab is never drawn in two windows at once.
• Desktop only. Web has no webview browser, and mobile has its own.

Known tradeoffs

• The page reloads when it moves between windows, because a <webview>'s guest can't be moved to another window. Logins are kept, but scroll position and form input are not. A move without a reload would need switching to WebContentsView, which is a much bigger change.
• Each pop-out loads its own copy of the web app, so it costs memory.

Implementation sketch

I have a working prototype on desktop:

• The pop-out is a plain BrowserWindow that loads a small data: page containing one <webview>. It uses the same partition and the same hardening as the main window's webviews, which now come from one shared helper.
• PreviewManager.registerWebview also accepts guests hosted by these windows. The pop-out's guest is registered under the same tabId and replaces the main window's guest.
• DesktopPreviewTabState gets a detached flag. While it's set, the main window unmounts its webview and shows a placeholder with Bring back. When it's cleared, the main window remounts the webview at the current URL.
• New bridge methods preview.tabWindow.open(tabId, partition) and close(tabId). The entry point is Pop out to window in the browser panel's ⋯ menu.
• Pop-out windows close with the main window or when their tab closes.
• Not done yet: the right-click menu and annotation overlays inside the pop-out, forwarding shortcuts (fix(desktop): Settings opens while the separate preview window has focus #28657), and remembering window position and size.

Related

• fix(desktop): Settings opens while the separate preview window has focus #28657: shortcuts sent to the main window when the preview window has focus. A pop-out window needs the same handling.
• fix(desktop): picture-in-picture stays sharp when the preview is scaled down #31568: picture-in-picture sharpness. That code may be replaced or kept as a lightweight "watch only" mode.
• [Bug]: Separate preview window input fails on Windows with a WSL-hosted browser #19673: the WSL-hosted, server-run browser. Out of scope here.
• [Bug]: Native popups opened with window features (pop-out players, OAuth) from desktop preview tabs are invisible to agents #30384: agents can't see popups that preview pages open in their own windows. A nearby multi-window problem.

Should the picture-in-picture window stay as a "watch only" mode, or should this replace it?