Use for the database & persistence layer — crates/persistence (the ONLY place ownership is written, in one YugabyteDB transaction), crates/cache (Dragonfly, ephemeral only), migrations, schema, the double-entry ledger, idempotency, and anti-dupe invariants. Delegate durable-state work here, NOT server gameplay/netcode (server) or anything that reads projections into the web (webclient).