The background task in lib.rs that emits playback:state to the frontend
sleeps adaptively: 250ms while playing, 1s when paused-with-track, and
5s when idle. The 5s idle branch leaves the seekbar blank for several
seconds on cold start because the loop only reads new state — and only
then emits — after the sleep ends, even though audio is already playing.
Add a tokio::sync::Notify (PLAYBACK_STATE_WAKEUP) shared via the
existing commands_v2::helpers module. Race the sleep against
PLAYBACK_STATE_WAKEUP.notified() with tokio::select. Each V2 command
that mutates playback state (play_track, pause, resume, stop, seek)
calls notify_one after the underlying bridge call succeeds, so the
loop wakes within milliseconds and emits the new state immediately.
notify_one stores up to one permit when no waiter is parked, so a
notification fired between iterations is delivered on the next select.
Make commands_v2::helpers a pub(crate) module so the static is
reachable from lib.rs and the V2 command modules.
cc
vicrodh
8288350559