The price chart keyed its X axis on formatLocalTime() "HH:mm" labels, which
repeat across a today+tomorrow range. Recharts resolves axis tooltips by value
(combineTooltipPayload -> findEntryInArray), so hovering a slot after midnight
matched today's identically labelled point: the tooltip showed today's prices
and the active dot jumped back to today's position instead of following the
cursor.
Key the axis on the ISO instant instead (buildChartRows, sorted by slot start)
and format down to HH:mm in the tick formatter; the tooltip label now carries
the date so today and tomorrow are distinguishable.
Also mark the price slot currently in effect by default: findActiveSlotIndex()
locates the slot containing now, rendered as a ReferenceDot on the buy and sell
lines plus a caption, re-evaluated every 30s.
Regression test drives a real mousemove over a sized chart in jsdom and asserts
the resolved slot and active-dot position.
tliu93
2f63b9630c