{
  "context": "Tests whether the response describes a safe zero-downtime column rename strategy.",
  "type": "weighted_checklist",
  "checklist": [
    {
      "name": "Uses expand-contract (multi-phase) approach",
      "description": "Describes a phased approach: add new column, dual-write, backfill, switch reads, remove old column — NOT a direct ALTER TABLE RENAME",
      "max_score": 15
    },
    {
      "name": "Explains why direct rename is risky",
      "description": "Notes that a direct column rename breaks running application code that references the old name",
      "max_score": 10
    },
    {
      "name": "Includes backfill step",
      "description": "Describes backfilling existing data from old column to new column (in batches to avoid locking)",
      "max_score": 10
    },
    {
      "name": "Mentions dual-write period",
      "description": "Application writes to both old and new columns during transition so no data is lost",
      "max_score": 10
    },
    {
      "name": "No incorrect information",
      "description": "PostgreSQL DDL behavior and migration strategy are technically correct",
      "max_score": 12
    }
  ]
}