migration-helper

> **AI-consumed reference.** Optimized for Claude to read during execution. > Human-readable explanation: see [docs/architecture/HIERARCHICAL_PLANNING.md](../../../docs/architecture/HIERARCHICAL_PLANNING.md) > or [docs/getting-started/](../../../docs/getting-started/) depending on topic. # Skill: Migration Helper Safe database and code migrations with zero-downtime strategies. --- ## Safety Rules 1. Always backup before migration 2. Test on staging first 3. Make migrations reversible 4. Deploy in small batches 5. Monitor during migration --- ## Related Rules - `rules/core/simplicity-over-complexity.md` — smallest migration that closes the gap; no "while we're here" schema expansions - `rules/core/verification.md` — verify each migration step before advancing - `rules/workflow/immutable-workflow.md` — migrations are append-only records - `rules/workflow/dual-llm-review.md` — destructive migrations (DROP COLUMN/TABLE) trigger dual-LLM review --- ## Schema Changes | Change | Safe Approach | |--------|---------------| | Add column | Add nullable → backfill → NOT NULL | | Remove column | Stop using → deploy → drop | | Rename column | Add new → copy → deploy → drop old | | Add index | CREATE INDEX CONCURRENTLY | | Change type | Add new col → migrate → drop old | ### Zero-Downtime (6 phases) Add nullable → dual-write → backfill → switch reads → remove old writes → drop old column. --- ## Migration Script Pattern ```typescript export async function up(db: Database) {...