Data Contract Migrations

Purpose

Use this skill when data shape changes can break reads, writes, reports, tenants, or integrations. The goal is an explicit compatibility and migration plan, not just a SQL diff.

Preflight

Gather these facts before proposing changes:

1. Current schema, models, serializers, API contracts, and persisted samples.
2. Writers and readers of each field.
3. Migration tool and rollback support.
4. Data volume, tenant boundaries, and backfill cost.
5. Required zero-downtime or maintenance-window constraints.
6. Existing tests or fixtures that prove compatibility.

If the current data does not contain a field, treat it as absent. Do not invent fallback fields.