Stopping the backend makes the native player fire its ended callback,
which lands in on_playback_ended. The timer thread cancels the timer
first, so by the time the callback inspects it the mode reads Off — the
sleep-timer branch is skipped and the episode path runs, showing a
next-episode popup (or advancing outright) right after the user's sleep
timer expired.
Record EndReason::UserStop before the stop reaches the backend. That is
the honest label: the stop was user-initiated, just via the timer they
set rather than the stop button.
TRACES: UR-023, UR-026 | DR-029
dtourolle
13e0860401