migration-safety-reviewlisted

# Migration Safety Review ## Install Save this file as `~/.claude/skills/migration-safety-review/SKILL.md`, or `.claude/skills/migration-safety-review/SKILL.md` to scope it to one repo. Claude Code auto-discovers it. Invoke with `/migration-safety-review` or by asking "is this migration safe to run?". ## Why this exists A migration is the one routine deploy step that can be unrecoverable. Application bugs get rolled back; a dropped column is gone unless someone happens to have a backup from before, and knows it, and can restore it under pressure. Two independent risks, and reviews usually catch only the first: 1. **Data loss.** Destructive and irreversible. 2. **Locks.** Perfectly reversible schema changes that hold an exclusive lock long enough to stall every query, taking the site down for the length of the migration on a table large enough to matter. The second is what turns a two-line change into an outage, and it never shows up in staging because staging has a thousand rows. ## Step 1 — Read the actual SQL, not the intent ``` # Prisma npx prisma migrate diff --from-schema-datasource prisma/schema.prisma --to-schema-datamodel prisma/schema.prisma --script git diff -- '*migration*' '*schema*' ``` Never review a migration from the ORM model diff alone. The generated SQL is what runs, and generators make destructive choices — a renamed field routinely becomes DROP plus ADD, which is a rename that deletes every value. ## Step 2 — Classify every statement **I