Both sliders now move a local draft (mpgDraft / fillUpDraft) and write once,
when the drag ends, via Slider's onEditingChanged. While the thumb is down only
this screen redraws: no store write, no fuelSavingsSettings mutation, and so no
app-wide recompute — ContentView re-ran its body, rebuilt the savings lookup,
and passed all 8,130 stations through the alert monitor on every step.
The drafts are Double?, where nil means "not dragging" and the stored setting is
shown. That falls back naturally after a commit, so the control shows what was
actually saved (the clamps can lower it) and anything changing the setting from
outside — a unit switch, the in-list control, a QA hook — is reflected without
any re-seeding.
The MPG and fill-up read-outs follow the draft, so the figure still tracks the
thumb.
The keychain write deliberately stays on the main thread: it is the
authoritative mirror on read, so an async write could hand a relaunch or a
widget a stale value. One write per gesture is cheap enough not to need it.
FuelBoard Contributor
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