`get_document_by_id`, `get_document_by_uri` and `get_chunk_by_id` read
through repositories a client covering a set does not have, so a lookup by
identifier raised AttributeError and `resolve_document` with it. An
identifier says nothing about which database holds it, so every database is
asked at once and the first that has it, in configured order, answers.
On the evaluation side, `--db` overrides the configured set as the CLI
documents, and population refuses a set rather than ingesting into a
database the run would not read. A case filter matching nothing raises
instead of reporting 0.0000 as though it were a score.