Firefox (and some download managers) issue a HEAD request before
starting a download. The route only registered GET, so HEAD returned
405 Method Not Allowed and the browser aborted the download.
Mirrors the pattern already used by /stream/{session_id}, which
registers both GET and HEAD on the same handler. ServeDirect is built
on http.ServeContent / ServeFile, which natively handle HEAD by
writing headers without a body, so no handler changes are needed.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
