[Bug]: Closing a server preview tab never fires beforeunload or pagehide#23513

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Serve a local page that reports its unload events:
   html

   1	<button>A</button>
   2	<script>
   3	for (const type of ["beforeunload", "pagehide", "visibilitychange"])
   4	addEventListener(type, () => navigator.sendBeacon(`/beacon?${type}`));
   5	</script>

2. preview_open it, and optionally preview_click the button (user activation).
3. t3_preview_close the tab.
4. Check the server log for beacons.

Expected behavior

Closing the tab runs the page's unload lifecycle, as closing a tab in a normal browser does, so pages that save or report state on pagehide/beforeunload behave the same under agent testing.

Actual behavior

No beacon arrives for any of the three events, with or without the prior click. dropTab (apps/server/src/preview/ServerBrowser.ts:675 on 680152e27b) calls tab.page.close(). Playwright's default is runBeforeUnload: false, which closes the page without running unload handlers.

Impact

Minor bug or occasional failure

Version or commit

T3 Code (Beta) 0.1.1 desktop; code reference from main @ 680152e27b

Environment

macOS 26.6.2, server-side preview (Playwright engine)

Workaround

None found.

Notes on a fix

page.close({ runBeforeUnload: true }) alone is not enough. With it, a page whose beforeunload handler calls preventDefault() raises a beforeunload dialog and stays open until that dialog is answered. T3 only records dialogs for preview_dialog, so the close would hang on a dialog no one answers. The close path would also need to accept that dialog (or decide not to). That changes what closing a tab means for pages with unsaved-changes guards, so I'd like to know the intended behaviour before proposing a PR:

• Should closing a tab (agent tool, Browser panel, idle close) run unload handlers at all?
• If so, should a beforeunload prompt during close be accepted automatically, or reported back to the caller like other dialogs?

Filed by Claude Code (claude-opus-5-5) for @DavidMendesOS.