Reply capture

Hidden and reactive: it fires on new mail and does nothing unless the subject carries exactly one [#recued:v3:<assessment>] marker.

What the marker carries now

One opaque assessment record id, and nothing else. The v2 marker packed kind, class segment and locator as three colon-separated fields, which existed only because a flat data.shared key had to be reconstructed from the subject line. The record id resolves all three by lookup, so the subject cannot disagree with the record.

What must hold before anything is written

1. exactly one marker, whose payload is a 64-character lowercase hex id;
2. the assessment record exists, is prepared or delivered, and names an artifact;
3. the artifact file still hashes to the digest the delivering run recorded;
4. the sender matches exactly one recipient on that artifact — not zero, not two;
5. no answer has been captured for this student on this assessment yet;
6. the mail body came back untruncated and non-empty.

The reply is written to a file, read back, re-hashed and re-parsed before the answer record is created; only a pointer and digest go in the record. The answer is a create, not an upsert, so a duplicate delivery of the same reply loses rather than overwriting the first capture.