d1c6774d05
Users declare artifact kinds in [[artifacts]] (id + schema_path to a JSON-schema file + llm_emitted); ConfigArtifactKind registers them at startup via createWorkflowLoader(extraKinds). New JsonSchemaValidator validates any non-built-in kind generically against its declared deriveJsonSchema(), so an LLM-emitted custom kind is checked against its shape, never trusted. Removed the dead payloadSerializer from the ArtifactKind contract. Schema source is path-to-file (not inline TOML — the hand-rolled parser can't nest).