Package	Role	ctx key
`session-registry/`	The seam: abstract registry service contract and record vocabulary	`ctx.sessionRegistry`
`session-registry-file/`	Backend: one lock-guarded JSON file, pid-derived liveness	—
`session-registry-live/`	Publisher: follows session lifecycle and title events, keeping the registry in step	—

The split follows the three-package capability-seam convention: the seam answers "what is live" for a short-lived reader that mounts nothing else, the file backend owns today's medium and can be replaced by a database without touching consumers, and the publisher needs the session store and runs inside a full agent composition. Liveness is derived from the recorded pid at read time rather than stored, so a killed process leaves nothing to clean up. Records carry their own title because log location, format, and compression are per-deployment backend choices an independent reader cannot portably parse.

This family is independent of session persistence: it records which processes hold which sessions, never conversation content, and a session that is never persisted still lists.