`handleInput()` called `stopProgress()` and mutated no reactive state,
so Lit scheduled no update, `updated()` never ran, and the tail of
`updated()` that restarts the interval never executed. Only a `change`
event or the next backend report could bring it back — so an `input`
that never commits froze the interpolation: a drag cancelled outside
the element, a pointer taken by a scroll, or a touch on the track
treated as a scrub, all ordinary gestures on a phone. While playing the
1 Hz report papered over it within a second; with reports not arriving
it was permanent.
The drag is `@state` now and `updated()` decides whether the interval
runs, so there is one place that knows. `handleChange` no longer starts
it directly for the same reason.
A flag set on `input` can strand, which would turn a stall of up to a
second into a permanent one — the failure this removes. `change` is the
ordinary end; `pointerup`/`pointercancel`/`touchend`/`touchcancel` on
the document are the ends that are not, attached with the drag and
dropped with it, because the pointer is routinely released outside the
element it started in.
The other half is that a report arriving mid-drag used to overwrite
`seekValue` and pull the thumb out from under the finger once a second.
It is skipped while dragging, and its seq is deliberately left
unrecorded so the first report after the drag still counts as fresh.
Three tests, all exercised against the fault: two fail on the old
component, and the third fails if the drag flag is left set — which is
the failure mode the fix introduces and the listeners exist to prevent.
Verified on the device too (Chrome 113): mid-drag the bar holds its
value and ignores reports, and on release it adopts the backend's real
position and resumes ticking.
Closes#164
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fe1fbefee7