Atomically append Event only while Key still has Expected. This is the compare-and-append primitive used for non-terminal long-running tool progress, so a racing terminal resume either happens wholly before or after the progress event.

Remove invocation-scoped temp: state after an invocation has completed.

Atomically replace an exact chronological event prefix with a durable compaction summary. Events appended concurrently after the prefix survive.

Initialize the session storage.

Atomically read and remove one state value. Missing sessions and missing keys both return {error, not_found}.