Save state and shut Claude sessions down cleanly when Windows shuts down or logs off #167

This was generated by AI during triage.

Summary

When Windows is shutting down or the user logs off, save state and shut Claude sessions down properly. Today CSM does nothing special, and the OS kills it partway through.

Current behaviour

There is no SessionEnding / WM_QUERYENDSESSION handling anywhere in the code. On reboot or logoff:

• OnClosing's orderly shutdown (the shutdown board, per-session exit waits, ClaudeShutdownBudgetMs) may never run, or may be cut short;
• state.json may miss changes made since the last save. Most saves are fire-and-forget and debounced;
• claude.exe children are killed without writing their config. That is the unlocked ~/.claude.json race that the shutdown loop exists to avoid.

Herdr fixed exactly this in v0.9.4 ("Restarting a Mac or shutting down Windows keeps your agents' sessions. Herdr saves before the system starts closing apps"). Its Linux build asks logind for a shutdown delay.

Proposal

1. Save first. Handle Application.SessionEnding (WPF), or WM_QUERYENDSESSION on the main HWND. Do a synchronous final SaveStateAsync first; it is the one thing that must land.
2. Ask Windows for time. Call ShutdownBlockReasonCreate(hwnd, "Saving N agent sessions…") so Windows shows the reason and gives the app time.
3. Shut down sessions. Run the existing Claude shutdown loop under a shorter budget, then ShutdownBlockReasonDestroy.
4. Measure first. Windows force-terminates after a few seconds unless the user waits. Measure how many sessions get a clean exit before choosing the budget (see the measurement notes on ClaudeShutdownBudgetMs).

Notes

• Log every step to crash.log. A shutdown is otherwise unobservable.
• Don't add a confirmation prompt. The user has already chosen to shut down.