GUI exits even when the final project save fails #375

Summary

The window-close handlers quit unconditionally even when Studio::close_project() fails to save and deliberately keeps the session open. This can silently discard unsaved edits on disk-full, permission errors, or a disconnected project volume.

Versions inspected

• v0.2.7, commit 14b5998
• main, commit afe8383

Source evidence on main

• src/crates/concat/src/studio.rs:7236-7240: final save failure triggers a notification and returns without closing the session.
• src/crates/concat/src/lib.rs:465-482: titlebar and system close handlers ignore this outcome, hide the window and/or quit the event loop.
• File > Close Window has the same pattern.
• src/crates/concat/src/panes/settings.rs:844-849: version-switch quit also ignores the failure.

Suggested reproduction (not yet executed)

1. Create a disposable project and make edits.
2. Make project manifest writes fail, for example using an isolated full test volume.
3. Close the window before obtaining a successful save.
4. The handlers currently quit even though saving failed; the error toast cannot remain visible.

Expected: keep the window/session open on save failure, show the error, and let the user retry. Do not quit or perform the version switch until saving succeeds (or explicit discard is offered).

Validation and contribution

This report is based on source analysis, not a reproduced runtime session. No claim is made that the Rust build or GUI test suite has passed. An AI-assisted, narrowly scoped fix is being prepared; all reported findings require human/maintainer review. The possible loss window is not necessarily limited to the autosave debounce if previous saves were also failing.