What to build: A Volume gains two stored fields of *about-ness*: a prose description and a list of subjects, filled from the bibliographic sources the app already queries (Open Library, Google Books, knihovny.cz/databazeknih — whichever answer for the Volume's identifiers). They fill in automatically during capture/lookup like other metadata (blank-fields-only, never overwriting), are editable by hand, and are shown on the book detail. For the existing catalogue there is an explicit "enrich" action: per-Volume on the edit form, plus a bulk pass that walks Volumes still lacking description/subjects and reports how many it filled, respectful of the sources (throttled, resumable if interrupted).
These fields are private for now (not in the public payload); their main consumer is ticket 08. Backups must include them.
Blocked by: None — can start immediately.
Status: ready-for-agent
source offers them, without overwriting user-entered text
are hand-editable like any other field
reports filled/unfilled counts
through backup and restore