[Phase 4] Optional watched folders with explicit opt-in automation rules #12

Priority: P3 / later
Parent roadmap: #1
Dependencies: #4 operation jobs and preferably #11 recipes.

Goal

Allow common file-processing operations to happen automatically when new files arrive in designated folders, while keeping Tuck lightweight when automation is disabled.

Product scope

• Rules: watched directory, supported extensions/file types, triggering conditions, selected built-in action or previously saved recipe, output directory, and enabled/paused status.
• On first creation explain what will happen; make it easy to disable a rule or pause all watchers. Never watch all of ~/ by default.
• Trigger only when a file has finished arriving/is stable; debounce bursts, avoid processing partial writes and safely handle filesystem event coalescing.
• Exclude generated outputs and prevent loops (watching export/ or an output that itself matches the rule).
• Idempotency tracking avoids repeated processing on restart or a rename.
• Respect permissions, external-drive dismount and offline/missing watched folders; never silently redirect output to a different volume.
• Define explicit app launch/background service behavior and power impact. No always-on helper if no rules are enabled.

Acceptance criteria

• Adding/pausing/removing a rule works without requiring a reboot.
• New stable matching files enqueue once; temporary/incomplete files do not process.
• Loop-prevention works for recipes producing matching file extensions.
• Errors are visible in Jobs/history, with optional nonintrusive macOS notifications.
• Disabled rules cause no ongoing directory scans or background processing.
• Rules survive restarts, bookmark changes and volume unmount without destructive fallback.

Tests

Rapid burst creation, rename storms, file writes in progress, nested dirs, duplicate events, output loops, missing permissions, restarts and external-volume disconnects. Evaluate FSEvents/DispatchSource APIs and security-scoped bookmarks rather than relying on frequent polling.