Matrix m.audio/m.file/m.video events populate content.body with the
uploaded filename when the sender adds no caption. The adapter already
blanks that for m.image (PR #16821, issue #13482) but not for audio,
file, or video msgtypes, so the filename survives into event.text and
is appended after the transcript, where the model reads it as the
user message rather than as transport noise.
Extend the existing adapter-level blanking: add
_looks_like_matrix_media_filename() with the same conservative
heuristic (single token, no whitespace, no path separators, known
media suffix or mimetypes audio/video match) and apply it at the
media message handler for m.audio, m.file, and m.video.
Salvage of #87968 by @AiwendilInTheWoods — reworked from shared
gateway path to adapter-level fix for consistency with the existing
m.image blanking.
fe8c9f1c92