`create_mcp_server` promised one database and accepted a scope covering a set,
where the write tools exist and fail on use. It refuses that now.
Resolving is the public factory's job, as it is `HaikuRAG`'s: `_covering` takes
a scope someone already resolved, so the configured name survives without a
`DatabaseScope` reaching the public signature.
The test that a scope decides the database asserted `all(...)` over a search
that could return nothing, which held whatever the server read. It reads the
listing instead, so alpha's documents being present and beta's absent both have
to be true.
The test searched through the capability, which embeds the query, so it passed
against a local Ollama and failed CI where there is none. What it exists to show
is that a lent client is what the capability reads through: `_ensure_rag`
returns it, and a full-text search through it names its results.
`reader_for` returned itself before looking at the name, so an "alpha" client
answered `reader_for("beta")` with alpha's reader. A citation naming another
database would have been read from the wrong one.
Both paths decide through `clients_covering` now, so one database refuses a
wrong name the way a set already did.
The chat citation test said mounting lends the client without showing it; a
chat test shows it and the docstring points there.
`reader_for` documented None as covering any database it could not place, but a
name outside the set raises `KeyError` like `clients_for` does: provenance
naming a database this client does not cover is wrong rather than absent. None
means one thing, a federated client given no name.
`sources=[]` means two things. On a search it selects nothing to search; on the
constructor it raises, since a client over no database can do nothing. Both are
written down now.
A capability reads through a lent client, so what a citation records is that
client's database and not the scope the capability was built with. Chat lends
one, and had no test saying so.
`format_for_agent` named the database whenever one was named, so a search over
a single named database carried a line with nothing to distinguish. It now takes
`include_collection` from the caller, which decides from the search selection
rather than from the hits: a search that could have drawn on two collections
names them even when everything came back from one.
`Collection:` at the model boundary, database in configuration and
administration. `source` on results, documents, citations and analysis
dictionaries is unchanged.
Two files of 1,405 and 814 lines become seven: scope resolution, lifecycle,
search, documents, expansion, citations and capabilities. `_config`, `_seed`
and the rest move to `helpers.py`, importable by the sandbox tests that share
them, and the package points VCR back at `tests/cassettes/multi_db/`.
