# Module 5 reference engine (Rust)

The course's own engine as of the end of Module 5. Every card is now data: a JSON file in the course's card format (`course/schema/card.schema.json`), and the Rust functions that were card effects in Modules 2–4 are gone. One interpreter turns effects into actions. Assemble builds a new card by replacing half of one card's text with the same half of another's. Module 4's reference was the starting point, so a diff between the two shows what this module adds.

- `cards/` (at the crate root; not in this directory): the card data. It is a copy of `course/cards/`, the single source: `tools/verify-references.mjs` stages it next to the crate, and `tools/start-module.mjs` copies it into a learner's workspace.
- `src/engine/`: generic machinery. Names no cards.
  - `card.rs`: the card format as Rust types (`CardDef`, `Clause`, `Effect`, `Target`, `Aura`, read with `serde`), and the library. Registering a definition compiles its clauses into triggers, auras and a spell's effects, and marks whether Assemble may offer it (minions with text that were not themselves assembled). `TriggerOn` gains `EndOfTurn`, which card data may name (Drakkari Enchanter's aura does); the course has no turns, so nothing fires it.
  - `effect.rs`: the interpreter: one effect plus its context in, actions out. The only code that knows what `dealDamage`, `draw`, `summon`, `assemble`, `buffHand`, ... mean.
  - `assemble.rs`: `assemble(base, donor, half)` (list surgery on `text` at `split`; fails with `AssembleError` if the text is unchanged), and the `assemble` effect, which asks the chooser for a base from the filtered pool, a donor and a half.
  - `queue.rs`: as in Module 4, plus two actions (`Assemble`, `Buff`). An ability's effects are interpreted and performed one at a time, in printed order.
  - `world.rs`: as in Module 4, plus card registration, cost, the chooser, and `buff`.
  - `aura.rs`, `death.rs`, `event.rs`: unchanged from Module 4.
- `src/content/mod.rs`: reads every `.json` file in `cards/`. No card is named in Rust any more.
- `src/harness.rs`: the adapter the course tests call. Module 5 adds `register_cards`, `assemble`, `cost` and `set_chooser`.

Run it with the module's tests: `node tools/verify-references.mjs 05` from the course repository. `cargo test` in this directory alone fails: there is no `cards/` here.