Without this the #638 fix is intermittent: the L1/L2 audio cache is
keyed by track id alone with no quality dimension, so a track warmed at
the old tier keeps serving local plays and casts at that tier until it
ages out. Clear both tiers the moment the Settings dropdown lands on a
different key (no-op re-selects do not clear).
The clear is fire-and-forget, deliberately not deferred: deferring
would let the next play after a change still deliver the old tier,
which is exactly the intermittency this exists to remove. Known cost,
accepted: an armed gapless handoff can drop (one possible audible gap
on an explicit, rare user action) and warmed bytes for local playback
are discarded too. Logged at info so a reported gap is attributable.
Protected-crate note: the qbz-player change is one pub fn on Player
that purely delegates to the already-existing AudioCache::clear()
(which clears both L1 memory and L2 disk). No engine logic, no contact
with playback_engine.rs or any sample-rate handling.
cc
vicrodh
a7cdab8810