For tools that declare `is_idempotent() == true`, successful results are
cached per-job so repeated identical calls (common during self-repair
recovery, stuck job retries, or chat-mode retry loops) return instantly
without re-executing. Cache uses SHA-256 content hashing with TTL and
LRU eviction, scoped per job_id.
Co-Authored-By: Claude Opus 4.6 <[email protected]>