Concept-Check: The Core

Kind: Quiz. One pass over the whole arc before you move on.

The Core arc installed the vocabulary every other arc speaks: id newtypes that the compiler keeps apart, status enums that serialize snake_case, an error taxonomy whose type answers "should I retry?", the WorkerHandle seam the distributed layer plugs into, and the tagged wire Message. This check mixes compiler-verified tracing questions with judgment questions across all of it.

If a question stings, the fix is upstream: Newtypes and Transparent serde for the id and status questions, and An Error Taxonomy That Knows What to Retry for the retry and #[from] questions. Re-read the section, then come back — the last five arcs stand on these types.

Next: Part III, the Eval Workload arc — a ModelClient trait object tested against a mock HTTP server, and the append-only file contract that logs every raw response.