#23744: fix(memory): add max size eviction to session manager cache

## Summary - Problem: Session manager cache (`SESSION_MANAGER_CACHE` Map) grows without bounds as new sessions are tracked, with no maximum size limit - Why it matters: In long-running gateway instances with many unique sessions, unbounded cache growth causes gradual memory pressure - What changed: Added a max size limit (500 entries) with LRU-style eviction of oldest entries when the limit is exceeded - What did NOT change: Existing TTL-based cleanup logic is preserved; cache behavior for entries within the limit is identical ## Change Type - [x] Bug fix ## Scope - [x] Gateway / orchestration - [x] Memory / storage ## Security Impact - New permissions/capabilities? No - Secrets/tokens handling changed? No - New/changed network calls? No - Command/tool execution surface changed? No - Data access scope changed? No 🤖 Generated with [Claude Code](https://claude.com/claude-code) <!-- greptile_comment --> <h3>Greptile Summary</h3> Added a max size limit (500 entries) with LRU-style eviction to prevent unbounded growth of `SESSION_MANAGER_CACHE`. The implementation leverages Map's insertion-order iteration to evict oldest entries when the limit is exceeded. - Introduced `MAX_CACHE_SIZE` constant set to 500 - Added eviction logic in `trackSessionManagerAccess` after setting new entries - Off-by-one issue: cache can grow to 501 entries before eviction (checks size after insertion) <h3>Confidence Score: 4/5</h3> - Safe to merge after fixing the off-by-one error in the eviction check - The implementation correctly addresses unbounded cache growth with a sensible max size and LRU eviction. The off-by-one error (checking `>` instead of `>=`) allows the cache to grow to 501 entries instead of 500, but this is a minor issue that doesn't compromise functionality - just allows one extra entry temporarily - Fix the eviction threshold check in `session-manager-cache.ts:35` _{Last reviewed commit: 2ad97e9} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->