[leiysky]

Summary

• Reuse the previous head returned by L1 directory insertion and classify the previous L2 slot directly, removing a duplicate lookup and slot re-encoding under the existing locks.
• Let reclaim scanning track when reinsertion stops. Budget-fitting records then skip payload checksums before conditional removal; over-budget records still validate payloads to preserve the budget-skipped count. Accepted reinserts still drain before releasing the source Region, independently of activity statistics.
• Extend the existing reclaim regression test across accepting, rejecting, and disabled sinks, retaining corruption, rewrite-byte accounting, and payload-lifetime checks. Update the architecture and changelog.

Validation: cargo x check, cargo x test (372 Rust tests and 9 Python tests), and cargo x lint all passed on macOS arm64. No throughput benchmark was run for this change.