The engineering recipe for the permission half, in six steps: normalise ACLs across SaaS sources, attach them to every chunk with a version number, pre-filter at the vector store, post-filter through a fine-grained authorisation service (SpiceDB, OpenFGA), fall back to the source system when metadata goes stale, and log every retrieval including what was denied. Vendor content, and it shows in what gets hand-waved, but the checklist itself is sound and executable.