PrivatewasPrivateprobeThe level the current entry's probe chose this frame, so the kick that
actually starts its reload can mark it (playbackProbePending).
Start of an evaluated frame: on the playback FALLING edge forget every probe mark, so a later unrelated load (a paused refinement, a preload) blends into the average instead of replacing it, and the next playback starts without a stale admission.
End of an evaluated frame (or of one entry): no probe is pending a kick.
During playback, the finest level at or below desired that can reload
within the admission budget of periodMs: an eager level (no
ensureLoaded — the per-slice sweep carries it), an unmeasured one, or
one whose loadEwmaMs fits. Once per probe interval, the next finer
capped level is probed for a warm-load sample. desired is unchanged
when not playing (periodMs null).
A timed (re)load of c just started: when it is this frame's probe, its
timing replaces the level's average.
PrivateprobedPeriodically re-measure the next finer capped level after a cold load. The
probe's reload replaces the level's average (playbackProbePending,
set when that reload starts): the samples it holds are at least a probe
interval old.
Per-registry playback state: the playing edge and this frame's probe.