Snapshot absent capture metadata before queued photo persistence

Queued photo persistence must snapshot both metadata and its absence before awaiting earlier work. When image uploads are content-addressed, a later capture can return the same URL while carrying different framing metadata. Using snapshot ?? latestMetadataForUrl can then attach the later guide to an earlier unguided photo. Represent explicit absence separately from an unspecified argument; only a direct call without a snapshot may consult current capture state.

This applies to client queues that reuse URL identities while retaining per-attempt diagnostics. It does not imply that content addressing is unsafe, or that a new table or capture ID is required for every application.

Applies when: per-capture metadata waits in a queue while content-addressed photo URLs can be reused. Keywords: camera capture metadata guide retry retake queue snapshot absence content addressing