Three places identified a picture by document and reference alone, and one
identified a citation's images by chunk id alone. Both repeat between copies of
a database, so a search returning a figure from two collections sent one, a
capsule retained one, and a citation rendered the other collection's figures.
Keyed on the source as well: `(source, document_id, self_ref)` for search
pictures, the capability and source for retained ones, and `qualified_id` for
the chat's citation images.
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