BMAD Migration Planner

## Migration Plan: Add payment_status to orders\n\n### Pre-Migration\n- [ ] Backup orders table (pg_dump --table=orders)\n- [ ] Test on staging with 2.3M row dataset\n- [ ] Notify on-call team\n\n### Migration Steps (zero-downtime)\n```sql\n-- Step 1: Add column with default (no lock on Postgres 11+)\nALTER TABLE orders ADD COLUMN payment_status text DEFAULT 'pending';\n\n-- Step 2: Backfill existing rows in batches\nUPDATE orders SET payment_status = 'paid' WHERE status = 'completed'\n AND id IN (SELECT id FROM orders WHERE payment_status = 'pending' LIMIT 10000);\n-- Repeat until 0 rows updated\n\n-- Step 3: Add constraint after backfill\nALTER TABLE orders ADD CONSTRAINT chk_payment_status\n CHECK (payment_status IN ('pending', 'paid', 'failed', 'refunded'));\n```\n\n### Rollback\n```sql\nALTER TABLE orders DROP COLUMN payment_status;\n```\n\n### Validation\n```sql\nSELECT payment_status, count(*) FROM orders GROUP BY 1;\n-- Expect: no NULLs, all values in enum\n```