Closing the window with unsaved changes was a silent data-loss path — and worse,
a clean exit deletes the recovery file, removing the safety net too.
Fold quitting into the same unsaved-changes flow as file switches: one
PendingAction enum (NewFile / Open / Quit), one modal, one do_action, one
after_save handler. render_unsaved_prompt now also intercepts the window-close
request (CancelClose + queue a Quit prompt); Save & Quit saves then closes,
Discard & Quit closes now, Cancel keeps the window open. confirmed_close lets the
final programmatic close through instead of re-intercepting it.
Replaces the near-duplicate close-prompt/switch-prompt code with a single path.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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