One sentence for the agent: what these documents are.
The whole document, for holding in an agent's context. Null as for read.
Every document the context may see. Called often; keep it cheap.
The pages in a range. Briyah clamps the range to the document. Returning null means the document is not there after all.
Passages matching a query, best first. Only ever called with document ids
that list returned for the same context.
A host's documents.