Module watcher 

The transcript watcher (Feed 2): an engine-owned background task that scans ~/.claude/projects/**/*.jsonl for new and growing session transcripts and feeds the SessionsRegistry.

It exists to cover the two gaps a purely hook-driven feed leaves:

1. Discovery — a session that started before the daemon (or before hooks were installed) fires no SessionStart the daemon can see; its transcript file still appears, so the watcher discovers it.
2. The thinking window — between UserPromptSubmit and the first PreToolUse (~5–15s) no hook fires, but the transcript keeps growing, so the watcher marks the session working through the gap.

Per ADR-0052 the watcher parses only file presence and growth (size/mtime) — never the per-line transcript schema, which is explicitly internal and version-unstable. The session_id comes from the filename stem; cwd is left unknown (the encoded directory name is a lossy /→- transform that cannot be reliably reversed — the hook feed supplies the real cwd, and SessionsRegistry::observe never clobbers a known cwd with None).

Only transcripts touched within [RECENT_ACTIVITY_WINDOW] are surfaced, so a fresh daemon does not flood the registry with hundreds of long-dead historical sessions on its first scan — ancient files are recorded (for later growth comparison) but never announced.

Functions

spawn

Spawns the watcher loop, returning its JoinHandle.