Design problem: an agent plugin caches task context before injecting it into a system-message transform. Multiple root sessions and child sessions share one process. How should the cache be keyed and lifecycle-managed so context never leaks across sessions, and how should memory be bounded under concurrent sessions? Known constraints: cache lives in-process; transform runs before/during prompt construction; child sessions may inherit parent identity incorrectly if keyed too coarsely. Unknowns: exact session ID APIs available to the plugin; whether child sessions outlive parents; eviction policy preferences. Seeking: keying scheme, isolation rules, eviction/TTL bounds, and failure modes to avoid.