fix: open an approval window while another one has focus (closes #290)

The background centred each approval window on the last focused window,
which could be an earlier approval window still open. Headless Chrome
reports one as 1280x720, so the position came out where the browser refused
to create the window ("Bounds must be at least 50% within visible screen
space"), and the request failed with -32603 and no window. It now centres on
the last focused browser window.

Under load a test in the Chrome suite raised its prompt while the previous
test's window was still closing, and either hit that refusal or took the
closing window for its own. The runner now closes every approval window
between tests.

Model: opus-5-5

TODO.md

@@ -45,6 +45,17 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-05: A prompt raised while another approval window has focus opens a
+  window of its own ([#290](https://git.eeqj.de/sneak/AutistMask/issues/290)).
+  The background centred each approval window on the last focused window, which
+  could be an earlier approval window still open; headless Chrome reports one as
+  1280x720, so the new window came out where the browser refused to create it,
+  and the request failed with no window at all. It now centres on the last
+  focused browser window. In the Chrome end-to-end suite a test could raise its
+  prompt while the previous test's window was still closing, and then either hit
+  that refusal or take the closing window for its own; the runner now closes
+  every approval window between tests.
+
 - 2026-10-05: A token scale of zero decimals is tested
   ([#325](https://git.eeqj.de/sneak/AutistMask/issues/325)).
   `resolveTokenDecimals()` already used a scale of 0 from the bundled list or