Start or reuse a private verifier derivation run

Snapshots one explicit UTF-8 Markdown instruction file or one tar.gz skill bundle and starts, joins, or retries verifier derivation for the URL org. Skill bundles contain SKILL.md at archive root plus optional references/, scripts/, and assets/ files. Unsafe paths, invalid archives, unsupported content, and inputs over the published limits are rejected. Identical uploaded bytes and input type reuse the same org-owned run; expectedFilename is metadata and does not change run identity.