db-runtime-clientlisted

# DB Runtime Client vs Migration Client Two separate database configs against the same Postgres instance — conflating them causes connection exhaustion under serverless load. 1. **Runtime client** (data-access layer, server handlers): **connection pooler, transaction mode** (e.g. port 6543 on Supabase). Only client application code imports. 2. **Migration client** (migration tooling/CI only): **direct** connection string. Never imported by application code. ## Rules - One config per purpose; don't leak migration connection into app layer - "Too many connections" in production → check if direct connection used at runtime by mistake Cursor equivalent: `.cursor/rules/db-runtime-client.mdc`