Safe Database Migration Plan

Turn a schema change into forward migration, data backfill, verification and rollback steps.

Create turn a schema change into forward migration, data backfill, verification and rollback steps.

Use these inputs:
- current schema: [current schema]
- desired change: [desired change]
- data volume: [data volume]

Return the finished result first. Then add a short assumptions note and three practical improvements. Do not invent facts, research, testimonials or results. If one essential detail is missing, use the safest reasonable assumption and label it instead of restarting with a long questionnaire.