Migrate the schema / data on a live app

Change a deployed schema without breaking existing data: stage the schema change, install @convex-dev/migrations, write a backfill that makes old rows valid, run it, and verify before tightening the validator.

Workflow

1. Make the new field optional first (so deploy doesn't reject existing rows).
2. Install @convex-dev/migrations; write a migration that backfills/transforms existing rows.
3. Run the migration; verify all rows are valid.
4. Tighten the validator (make the field required) once the backfill is complete.

Rules

• Never tighten a validator before the backfill completes — it rejects existing rows and breaks the live app.
• Add new fields as optional first, migrate, then require.
• Verify row counts before and after.