Helps explain WHY each spawn goes warm vs cold. The existing
`spawn mode=warm|cold` log only shows the outcome at the spawn point —
to count where warmth is being lost, we need to see:
- when a session_id is recorded (and for which key),
- what every lookup returns (key + Some/None),
- when remove_sessions_for_story prunes (which is currently the only
explicit cold-induction path beyond "first ever spawn").
After this lands a grep of "session_store" in the logs gives the full
warm-resume health picture: which (story,agent,model) triples have a
recorded session, which lookups are hitting it, and which prunes are
costing us a warm respawn.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
dave
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