ReadonlyactiveReadonlyidReadonlynameOptional ReadonlyopenedWhen this workbook was (re)loaded in the client UI — its history epoch, epoch-ms.
Optional ReadonlypathThe workbook's file, when the client UI reports one.
The id is path-derived in current clients (stable across reloads), so the path is no longer the ONLY durable handle — but it still travels: it disambiguates two same-named files, it is the identity a consumer matches documents on, and an untitled workbook's id is per-load. Older clients omit it (and mint per-load ids), hence optional rather than required — an absent path degrades a report, a mismatched contract breaks one.
A workbook open in a client UI.
Remarks
The relay's own wire shape. Callers map it into whatever they hand onward.