feat(daemon): durable health state, divergence escalation, staleness checks, watcher pre-filter

[chrisleekr]

Why

For a backup daemon, the worst failure is a silent one. Today the daemon's failure state lived only in memory (lost on restart), there was no notification or staleness signal, a vault divergence made it retry a doomed push on every keystroke forever, and high-churn agent dirs (sessions/history) woke pushes that snapshot nothing. A user could go weeks with zero successful backups and no signal.

Fifth PR in the series (follows #184, #185, #186, #187).

What

• Durable health state — the daemon persists daemon-state.json (last success, last error, consecutive failures, stuck flag) and updates it on every success/failure, so health survives a crash/restart.
• daemon status now reports last-successful-sync age, failures, and a stuck flag, and falls back to the durable file when the daemon is down — you can still see when sync last worked.
• doctor gains a Daemon sync health row: fails when stuck, warns when installed but the last success is >24h old (or never), passes on a recent success. A silent backup failure is now loud.
• Divergence escalation — on DIVERGED_HISTORY the daemon latches stuck, fires one desktop notification (osascript/notify-send, best-effort), and backs off watcher retries to once per 5 min instead of hammering. A manual agentsync push is never throttled; the next success clears it.
• Watcher pre-filter — never-sync paths are filtered at the watch layer, so a noisy config dir no longer resets the debounce or wakes a no-op push.

Review fixes (caught in senior review)

Atomic temp+rename for the state file (no torn write on crash); ISO-datetime() validation on stored timestamps (a corrupt value degrades to empty instead of a misleading Date.parse NaN); isolated AGENTSYNC_DIR in the daemon test harness so tests never touch the real ~/.config/agentsync or fire real notifications.

Tests

state.test.ts (pure transitions incl. the stuck latch, persistence round-trip, corrupt-file degrade, formatAge); watcher shouldSkip filter; doctor health (stuck/never/not-installed/stale/recent); daemon status stuck-escalation, last-sync age, and offline durable-file fallback; daemon-index persistence-on-failure, startup-preserves-stuck, and health-field exposure. Full suite: 966 pass / 0 fail.

CI note

bun test exits non-zero on the per-file coverage floor; CI treats 0-fail as success.

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