## Why
Repeated repository skill discovery performs remote metadata requests even when no `.agents/skills` directories exist. Reuse verified empty results to avoid those round trips while watching for changes that require a new scan.
## What changed
- Add the Linux executor capability `fs_watch_missing`, the `fs/watchMissing` request, and `fs/missingChanged` notifications.
- Register watches in the background and reuse empty results only after the executor acknowledges coverage. Key reuse by filesystem, working directory, and project root markers.
- Invalidate observations on relevant filesystem or mount changes, watch supersession, or connection loss. Clear cached observations on forced reloads and cache resets.
- Retain live discovery while registration is pending or watching is unsupported, unavailable, or cannot verify the observation.
## Testing
Add tests for empty-result reuse and invalidation, skill directory creation before watch acknowledgement, unsupported executors, idle WebSocket notifications, reconnection, case aliases, and bind mounts and unmounts. Include an ignored manual latency comparison for repeated empty remote scans.
GitOrigin-RevId: 3ad499decefb184a99c068afa01d0dcdd8605c7f
adams-oai
28cade4f5a