Sub-ticket of MARS-145 Mars DB scaling: migrate serverless runtime from direct-5432 to Supavisor transaction pooler (6543); reserve direct-5432 for weekly-kpi cron + migrations/seed; cut runtime pg.Pool max 16->~3; audit+cap per-request concurrent-query fan-outs (mirror Pluto mapWithConcurrency); pre-flight named-prepared-statement check (txn mode drops them). 3-PM consensus bs-mql6kqmrm6j, Venus=reference (already on pooler). One-env-var + cron carve-out, reversible. · mars