A warm launch rewrote the entire session cache whenever any provider
appended a few KB: on a 6 GB corpus that is a 155 MB stringify + fsync
every run. The on-disk cache is now a version-suffixed directory holding
one shard per provider plus a small envelope, and a save rewrites only
the providers marked dirty.
- Dirtiness is tracked per provider (markCacheDirty) instead of one
global flag, so an appended Claude session no longer republishes
Codex, Copilot and the rest.
- Shards carry a nonce in their filename and the envelope is renamed
last, so a save is published at a single point: readers never see a
half-updated set, and a writer that loses the refresh ownership fence
leaves the canonical shards untouched.
- A shard that fails validation is treated as an absent provider rather
than rejecting the whole cache, so one malformed turn costs one
provider's re-parse instead of every provider's history.
- v7 migrates losslessly: the blob is re-laid-out into shards and
removed only once that save publishes. Nothing re-parses.
- Cold-parse progress saves now trigger every N files parsed rather than
every 5s, so a slow cold parse no longer rewrites the growing cache on
a wall clock.
