Provider-Portable Speech-to-Text API Intake — Diagnosing Malformed Multipart Form-Data

TL;DR: Treat a transcription upload as two separate checks. First, prove that the selected provider currently advertises a usable speech-to-text model. Then send a tiny known-good audio file with a multipart body generated by a library, including a filename, a credible audio MIME type, and the provider's exact file field name. A marketplace moderation pipeline should preserve the original report and make transcription retryable; it should never turn an ambiguous HTTP 400 into a dropped report. That order matters.