Fullscreen + WCO collapsed leaves top-right titlebar area non-interactive

#518849412 Filed 2026-06-01 Blink>Fullscreen Assigned Windows only

Summary

In an installed PWA using display_override: ["window-controls-overlay", "standalone"], entering browser fullscreen while Window Controls Overlay (WCO) is active leaves a non-interactive hit-test region in the top-right titlebar area. Mouse clicks in that region are swallowed even though app UI is visible there. Keyboard focus still works; pointer input does not. Exiting fullscreen restores clickability.

Conditions for the bug

Live state check

Install this page as a PWA, enter fullscreen (F11), then watch the conditions below. Note that navigator.windowControlsOverlay.visible reports false in fullscreen because Chrome hides the overlay UI -- but on Windows the native frame still reserves the caption hit-test region. That is why JS cannot feature-detect the dead zone: the only reliable signal is whether the top-right controls actually respond to clicks.

Simulated app titlebar

Click the top-right controls in fullscreen

Environment conditions

Reserved caption region: inactive

Click test

Click Ping and Menu above. If nothing registers here, the caption region is swallowing the clicks (the bug). With the fix they register normally.

No clicks yet -- try the top-right controls.

Informational

Fix

Drop the #if BUILDFLAG(IS_MAC) guard so WCO is disabled in fullscreen on every platform, and refresh the state on fullscreen enter/exit transitions.

CL 8027830 (LUCI passed) CL 7914489 (original) GitHub: Chrome-WCO-Bug-Lab Issue tracker

Reproduce locally

  1. Install this page as a PWA from Chrome on Windows.
  2. Open the app window, then press F11 to enter fullscreen.
  3. Keep WCO active / collapsed (caption area reserved).
  4. Click the Ping / Menu controls in the top-right of the strip above.
  5. On an unpatched build the clicks are swallowed; with the fix they respond.