bug(jobs): background jobs vanish without notice when the Pi process restarts #3201

Summary

Background jobs started with bash_background disappear without notice when the Pi process restarts. The registry is in memory (extensions/gentle-agents.ts:436-437) and the logs live under the per-process temp directory (lib/session-scratch.ts:18-20), which is replaced on restart; docs/gentle-shell.md:392 documents the removal on shutdown.

Impact

A 6-8 h watcher (wait for a runner, then run governed merges) vanished between two turns: job_list became empty, the log directory changed (gp9jXUbF -> gpwTD854) and no exit notice arrived. The agent only noticed because the user asked for status. No crash entry was recorded for that session, so the trigger of the restart is unknown.

Expected

After a restart, the session is told which jobs were lost (id, label, command, last known state), so the orchestrator can relaunch them, and ideally the restart reason is logged.