Keep focus in a confirmation when a disabled button drops it to the page

Confirm moved focus to its dialog only when the focused control stayed
focused while disabled. A browser that moves focus to the page as it
disables the control left the confirmation open with focus outside it.
Confirm now also takes focus back to the dialog when busy or dismissible
changes and focus is on the page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/settings/LeaveGuard.tsx

@@ -59,12 +59,14 @@ export function Confirm({
 }: ConfirmProps) {
   const titleId = useId()
   const sheetRef = useRef<HTMLDivElement>(null)
-  // A focused button that becomes disabled loses focus to the page, outside
-  // the dialog; the dialog takes it instead.
+  // A focused button that becomes disabled either keeps focus while disabled or
+  // loses it to the page, depending on the browser; the dialog takes it instead.
   useLayoutEffect(() => {
     const dialog = sheetRef.current?.closest<HTMLElement>('[role="dialog"]')
+    if (!dialog) return
     const active = document.activeElement
-    if (dialog && active instanceof HTMLElement && active.matches(':disabled') && dialog.contains(active)) dialog.focus()
+    const lost = active === null || active === document.body || (dialog.contains(active) && active.matches(':disabled'))
+    if (lost) dialog.focus()
   }, [busy, dismissible])
   function dismiss() {
     if (dismissible) onCancel()