barrel_record_docstore (barrel v1.0.0)

Read-through docstore adapter for record-mode databases.

Implements barrel_vectordb_docstore over the record's document database: search-result hydration reads text and metadata from the CURRENT document, rendered through the database's embedding policy. The document is primary; this adapter never writes or deletes it:

• get/multi_get: caller-side document reads (they run inside the vectordb server during search fetch, so they must not round-trip the docdb writer).
• put/multi_put: {error, read_only}. The record write path uses index-only vector writes and never produces doc pairs, so reaching this is a misuse of add/add_vector on a record store, and it fails loudly.
• delete: a no-op. Deleting a vector must never delete the document.
• terminate: a no-op. The barrel module owns the database lifecycle.