feat: daemon auto-update support with hourly check loop

[svarlamov]

Summary

Adds auto-update support to daemon mode. A new background thread wakes hourly to check if a newer version is available. When one is found, the daemon gracefully shuts down, and the installer runs post-shutdown to replace the binary. The next git command auto-starts a fresh daemon from the updated binary (via existing ensure_daemon_running()).

Changes:

• src/commands/upgrade.rs: Added DaemonUpdateCheckResult enum and two new public functions:
  • check_for_update_available() — queries the releases API + updates cache, no install
  • check_and_install_update_if_available() — reads cached update state, re-fetches release, downloads + runs installer silently. Intentionally bypasses the 24h time guard (reads update_available from cache instead) so the install actually runs after the hourly check already confirmed availability.
  • Both use Config::fresh() (not the OnceLock singleton) so the long-running daemon respects runtime config changes
• src/daemon.rs:
  • daemon_update_check_loop() — background thread sleeping in 5s ticks (for prompt shutdown), checks hourly
  • daemon_update_check_interval() — reads GIT_AI_DAEMON_UPDATE_CHECK_INTERVAL env var override (clamped to min 1s to prevent spin-loops), defaults to 3600s
  • daemon_run_pending_self_update() — called after clean shutdown to run the installer
  • Spawned as a third thread alongside control and trace listeners in run_daemon()
• tests/daemon_mode.rs: Three integration tests exercising the full daemon update thread lifecycle:
  • daemon_update_check_loop_detects_cached_update_and_shuts_down — seeds fake update cache, starts daemon with 1s interval, verifies self-shutdown with clean exit, lock release, and socket closure
  • daemon_update_check_loop_respects_disabled_auto_updates — same cache but auto_updates_disabled=true, verifies daemon stays alive
  • daemon_update_check_loop_no_update_stays_alive — no pending update in cache, verifies daemon remains running
• Unit tests for the new enum and update-check building blocks

Review & Testing Checklist for Human

• check_for_update_available cache-hit path: When should_check_for_updates returns false (not yet 24h), the function still returns UpdateReady if a previous check cached a pending update. This means the daemon could shut down on a stale cache entry from a prior non-daemon check. Verify this is acceptable.
• Post-shutdown install re-fetches release from API: check_and_install_update_if_available confirms the update via cache, then makes a network call to get the release tag for the installer. If the API is unreachable at shutdown time, the install silently fails (debug_log only) and the old binary continues. Verify this graceful degradation is acceptable.
• daemon_run_pending_self_update runs on every shutdown, not just update-triggered ones. Manual git-ai daemon shutdown will also attempt an install if a cached update exists. This seems correct but should be verified as intended.
• Integration tests don't cover the actual install step: The tests verify the check→shutdown sequence end-to-end, but the post-shutdown check_and_install_update_if_available() call will fail silently (no real release server). The install path is only exercised by the unit tests on its building blocks. Consider whether a mock release server test is needed.
• GIT_AI_DAEMON_UPDATE_CHECK_INTERVAL env var is not gated behind cfg(test): It's available in production builds to allow external testing. Verify this is acceptable or whether it should be debug-only.

Suggested manual test plan:

1. Build a debug binary, start the daemon (git-ai daemon run)
2. Manually write a fake update cache entry with update_available = true and a future version to ~/.git-ai/internal/update_check
3. Set GIT_AI_DAEMON_UPDATE_CHECK_INTERVAL=10 for a short cycle
4. Verify the daemon detects the cached update, shuts down, and attempts the install
5. Verify the next git command starts a new daemon

Notes

• Stacked on PR Async #743 (feat/async-mode-mar-17).
• No changes to install.sh or install.ps1 — Unix atomic mv works on running binaries, and Windows install.ps1 already has Wait-ForFileAvailable polling.
• The hourly wake interval is separate from the 24h API check interval — the thread just evaluates whether the cache has expired.
• The interval is clamped to max(1) to prevent a CPU spin-loop if the env var is set to 0.

Link to Devin session: https://app.devin.ai/sessions/f511157ae89e4449a7edb023a9c55cf7
Requested by: @svarlamov

---

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.