hydrate-first-party-blob-streams

The reference already exposes a grant-safe blob transport through blobref.fetchurl and GET /v1/blobs/{blob_id}, but first-party connectors mostly emit metadata-only records for files and attachments. Reviewers can discover that an email, statement, receipt, or uploaded file exists, but cannot fetch the bytes through PDPP even when the source account makes those bytes available.

The reference RS already has the core blob substrate:

The reference implementation SHALL use its existing blob substrate for first-party connector streams that collect binary file content. A connector that hydrates source bytes SHALL store those bytes through the reference blob storage seam and SHALL expose them to clients through a record blobref decorated with fetchurl at read time.