The Stems popover and Extract say nothing when an Apply does nothing, and say "applied" when it was not #793

What goes wrong

Unticking every stem and pressing Apply does nothing and shows no message. The Extract button on an open song shows "Lanes changed in . Nothing was separated again." for any reason except a recording or a failed split, including when no song is open or the mode has no lanes.

Who is affected

Anyone using the new per-mode stem choice.

How to see it

1. Open a song, open Stems, untick all stems, press Apply: the status line stays empty.
2. In a mode without lanes (for example Karaoke with the wrong state), press Extract aimed at the open song: it reports success.

Evidence

• static/js/stemsControl.js:41-46 (blockedText knows "recording", "noSong", "failed" only), :199-205.
• static/js/modeStems.js:116,133,135,141,172 return "noSong", "empty", "mode".
• static/js/job.js:786-791.

Constraints for anyone fixing it

• New text needs stems.* keys in all ten tables of i18n.js and the Guide entry for the popover (there is none yet).
• Behaviour must stay the same per mode (Practice, Advanced, Karaoke, Performance each save their own choice).

Origin

NEW in 0.21.0 (6665a21). Found on the big-release branch (draft pull request #784); the work is not released yet.

Possible direction

Map every reason to a message and show success only for success.

Verified by

read.