## Why
Persisted item snapshots can be updated after their initial projection while retaining their creation order. Callers need a way to read those updates incrementally without replaying every item.
## What changed
- Track the rollout ordinal of each item's latest snapshot separately from its creation ordinal.
- Let thread-store callers filter items after an exclusive update watermark and sort pages by either creation or update ordinal.
- Keep existing app-server reads creation-ordered, reject incremental reads across forked lineages, and preserve compatibility with older writers.
## Testing
- Cover update-watermark filtering, pagination, sort directions, per-turn reads, cursor validation, forked lineages, migration compatibility, and refreshed item snapshots.
GitOrigin-RevId: d57de849abec27f788e9c384dbff073a0aca1053
richardopenai
b834702b27