Flip the state.db retention defaults per Teknium's decision on #54189:
- sessions.auto_prune: false -> true. A stock install now prunes ENDED
sessions inactive for retention_days at CLI/gateway/cron startup
(at most once per min_interval_hours). Open, pinned and mid-turn
sessions are never deleted; the only open rows touched are stale
automation sessions (#100903 sweep), which are closed, not deleted,
and aged a further full window before removal.
- sessions.retention_days stays 90 (already the default; verified).
- Auto-VACUUM is now additionally gated on the reclaimable fraction of
the file: PRAGMA freelist_count / page_count must exceed 25%
(AUTO_VACUUM_MIN_FREELIST_RATIO) on top of the existing
min_vacuum_interval_days throttle. Pruning a few small sessions on a
dense multi-GB DB no longer rewrites the whole file to reclaim a few MB.
Unknown ratio (pragma read failure) falls back to the time throttle.
Existing installs that explicitly set any sessions.* key keep their
values (load_config deep-merges DEFAULT_CONFIG under user YAML); only
unset keys pick up the new defaults. No _config_version bump needed.
cli-config.yaml.example documents the section commented-out so
installers that copy it verbatim never pin these as explicit settings.
Tests: ratio gate (below/above/at-threshold/unknown/override), real-DB
freelist ratio, default assertions, fresh-config startup hook reaches
the prune call, explicit opt-out respected, template-does-not-pin-keys.
Teknium