Immutable content-addressed artifact versions with If-Match, lineage that must resolve under the caller, unified diffs, promotion; sources/passages/citations with server-side hashing and dedupe, citation integrity checks and revisioned research notebooks. Cross-tenant access is 404 and audited. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01RNPhwu2bsaRNg3DETSAZoM