pub fn concatenate_stems(slug: &str, tag: &str, filter: &str) -> Option<PathBuf>Expand description
_concatenate_stems(slug, tag, filter): every matching stem joined into
one cached MP3, keyed by the ordered (path, size, mtime) of its inputs so
a repeat click is instant and a re-produced stem rolls the key over.
Decoding goes through ffmpeg rather than pydub; this is a listening preview, not a pipeline artifact, so it only has to sound the same.