What problem does it solve? Designing a persistence layer without a plan leads to missing indexes, unclear data ownership, and irreversible migrations. This Skill produces a structured Data Model plus Migration Plan artifact so schema changes ship with backward compatibility and a rollback path. ## Core Features & Use Cases - Schema and Source-of-Truth Design: Defines tables, columns, types, constraints, and designates one source of truth per fact. - Index Planning from Access Patterns: Derives indexes from real query patterns and volume rather than guesswork. - Expand/Contract Migration Planning: Writes reversible expand, backfill, switch, and contract steps with a rollback for each, gated by human approval. - Use Case: When building a wallet ledger, use this Skill to define an append-only ledger table with a unique idempotency key, designate the ledger sum as the balance source of truth, and plan a nullable-column expand migration with a drop-column rollback. ## Quick Start Ask the agent to design the table schema and plan the migration for your feature, providing your domain model, access patterns, and expected data volume.
