Reported, with this on screen:
No se pudo iniciar la grabación: Invalid argument(s): Unsupported scheme
'content' in URI content://com.android.externalstorage.documents/tree/
primary%3AMusic/document/primary%3AMusic%2F...%2FNew Limit - Smile.mp3
The URI in that message is a local MP3, not a station.
PluriWaveAudioHandler._cambiarFuente sets `emisoraActual` for EVERY source
it plays, so a local track surfaces as an Emisora whose `url` is the SAF
content:// document URI it was opened from. EstadoGrabacion.iniciar only
checked for null, handed that straight to the recorder, and the HTTP
client failed with a message no user can act on.
"It used to work" is exactly right: before local music playback existed,
whatever was playing was always a real station, so the case could not
arise. The recorder never changed.
iniciar() now also requires a real network stream (esEmisoraGrabable) and
falls back to the existing "select a station first" message, which is the
correct guidance here -- recording a local file makes no sense anyway,
it is already on the device. No new l10n key, so no 13-locale churn for a
message that already says the right thing.
Tests: 1158 -> 1161.