[Bug]: Browser content lingers after closing the right panel

[Neel2107]

Before submitting

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

Area

apps/desktop

Steps to reproduce

1. Open T3 Code Desktop with a thread selected.
2. Open the right panel and select a browser tab with a loaded page.
3. Close the right panel while the browser tab is active.
4. Watch the browser content as the chat expands into the space previously occupied by the panel.

Expected behavior

The browser content should disappear in sync with the right panel closing, with no content left over the expanded chat.

Actual behavior

The panel closes and the chat expands, but the browser content briefly remains visible over the chat before disappearing. The panel layout and browser content visibly close out of sync, making the transition look laggy.

This happens twice in the supplied recording when the panel is opened and closed. The browser page is already loaded when the panel is closed.

Impact

Cosmetic issue: browser content temporarily covers the chat during the close transition.

Version or commit

Exact version/commit not confirmed. The recording shows T3 Code (Nightly).

Environment

macOS, T3 Code Desktop (Nightly), embedded browser in the right panel. Observed on September 6, 2026.

Supporting evidence

Screen recording showing the delayed browser disappearance:

Screen.Recording.2026-09-06.at.8.33.44.PM.mov

Related issues

• [Bug]: Floating preview moves to the middle after closing the side panel #6546 concerns an intentionally floating preview staying in the wrong position after closing the panel. This report concerns the panel's browser content briefly lingering before disappearing.
• [Bug]: Failed browser preview remains as a blank floating panel #7212 concerns a failed preview remaining as a persistent blank floating panel.

[juliusmarminge]

Triage

Thanks for the report. This looks like a real cosmetic desktop bug, not a duplicate of #6546 or #7212.

#6546 / #6547 were about an intentionally floating mini-player staying in the wrong place after the side panel closed. #7212 is a failed preview left up as a blank floating panel. This one is the docked right-panel browser staying painted over the chat for the close animation.

What the code is doing

The inline right panel keeps its content mounted through the close transition via usePanelPresence (apps/web/src/panelAnimations.ts) so PreviewPanelShell can animate width to 0 with overflow-clip (apps/web/src/components/preview/PreviewPanelShell.tsx). That clips the HTML chrome, but the desktop guest is a position: fixed <webview> hosted by ElectronBrowserHost / HostedBrowserWebview, positioned from BrowserSurfaceSlot’s unclipped getBoundingClientRect(). CSS overflow does not clip that guest, and the slot does not observe the width transition, so the page stays at full size until presence times out and the slot unmounts.

ChatView currently passes visible (always true) into PreviewPanel for the whole presence window. The terminal surface already passes visible={rightPanelOpen}.

This should only show when Appearance → panel motion is greater than the default 0 ms.

Suggested fix

Hide the hosted surface as soon as the panel starts closing (visible={rightPanelOpen} into PreviewPanel / BrowserSurfaceSlot), matching the terminal panel. On macOS, park the guest offscreen rather than using visibility: hidden — HostedBrowserWebview already does that to avoid Electron 43 blanking.

A nicer follow-up is intersecting the presented rect with the clipping ancestor during the width transition so the page shrinks with the panel instead of disappearing immediately.

Not doing here

No code change or PR from this triage. The mentioned recording is not attached; it would help QA, but it is not required to start the fix.

Severity: low / cosmetic
Type: bug

[Neel2107]

@juliusmarminge I have attached the recording.