Produces a data model for a new domain — access patterns, entity definitions with fields and constraints, relationships and cardinality, indexes tied to access patterns, evolution considerations, and explicit trade-offs. Use when the user says "design the schema/data model", "tables for [feature]", "how should I model X", or describes a domain needing storage. Use this to design the schema for a chosen database; use database-selection-guide to choose the database first, and api-contract-design for the request/response shapes rather than the storage layout.
