Wrap insertChunk in a synchronous better-sqlite3 transaction that upserts
agent_metrics counters atomically on every chunk insert. Malformed JSON
skips the upsert but always preserves the chunk row.
Add findMetricsByAgentIds to the interface and Drizzle adapter for
efficient bulk metric reads.
Add 8-test suite covering all write/read paths and edge cases.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
6eb1f8fc2a