Creation validates the vocabulary and the registry, failing fast with
MilanoEngineError on developer mistakes: InvalidVocabulary when the
artifact violates the spec, IncompleteRegistry when a declared
component type has no registered renderer.
ReadonlydefaultReadonlyfunctionReadonlylimitsReadonlyobserverRetained for the engine's lifetime, like the other runtimes.
ReadonlyregistryReadonlyuserReadonlyvocabularyA builder for one document, given as text or as raw bytes. With bytes, the document-size limit is checked against exactly those bytes.
The long-lived object: one vocabulary, one registry, one policy, and the resource limits. Immutable after creation and safe to share; every view is built from it.