Feature: FSEvents-based real-time monitoring (macOS, optional)

[BrunoO]

Summary

Optional enhancement: Add real-time file system monitoring on macOS using FSEvents, so the index can be updated when files change on disk without relying only on --index-from-file or manual re-crawl. This would bring macOS closer to Windows USN Journal behavior (real-time index updates when the monitored volume changes).

Current state

• Windows: USN Journal provides real-time monitoring; index stays in sync as files are created, modified, or deleted.
• macOS: No real-time monitoring; index is populated via folder crawl or --index-from-file and does not auto-update when the filesystem changes.

Goal

• Use FSEvents (or equivalent macOS API) to watch the indexed volume/folder.
• On create/modify/delete events, update the in-memory index (add, update, or remove entries) so search results reflect current disk state without a full re-crawl.
• Design should align with existing index-maintenance patterns where possible; platform-specific code isolated.

Non-goals (for this issue)

• Changing Windows USN behavior.
• Linux inotify/FANOTIFY (separate future work).
• Replacing --index-from-file; it remains valid for one-off or batch indexing.

References

• Feature parity note: internal-docs/archive/PHASE_2_FEATURE_PARITY_GOAL.md — macOS currently “Real-time monitoring: ❌ Not supported”.
• Optional Phase 3 / future enhancement mentioned in related archive docs.

Priority: Optional / future; no blocking dependency.