[HIGH] O(n) LRU eviction on every insertion at capacity

[ironclaw-ci]

[HIGH:100] Issue Found by Staging CI Review

Severity: HIGH
Confidence: 100/100
PR comment: #1428 (comment)

Description

O(n) LRU eviction on every insertion at capacity

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Auto-created by staging-ci Claude Code review

[henrypark133]

Triage: LEGIT but ACKNOWLEDGED — The code has an explicit TODO comment (line 105-107) acknowledging the O(n) eviction. The batch path already uses the optimized evict_k_oldest() with partial selection. Single-embed eviction at 10K entries is ~microseconds (iterating Instants). Switching to the lru crate is a future optimization if max_entries grows.