[richardopenai]

Summary

• extend ListItemsParams with an optional (after_updated_at, through_updated_at] interval
• require stores to return Unsupported instead of silently ignoring timestamp bounds
• echo the applied upper bound in ItemPage
• add a ResourceExhausted error for implementations with hard response limits

Why

ThreadStore implementations need one canonical contract for incremental latest-state item reads across opaque cursor pages. Keeping the interval on list_items avoids parallel store APIs while preserving existing unbounded behavior for callers that omit both bounds.

Validation

• just test -p codex-thread-store — 89 passed
• cargo check -p codex-app-server
• cargo fmt --all -- --check