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fix(hl): biggest day marker always from displayed series#548

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Merged
Flotapponnier merged 1 commit into from
Jun 18, 2026
Merged

fix(hl): biggest day marker always from displayed series #548

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32 changes: 23 additions & 9 deletions src/components/hl-performance-chart.tsx
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Original file line numberDiff line numberDiff line change
Expand Up@@ -158,15 +158,22 @@ function ChartCanvas({
// Area path: same poly-line, closed back to the baseline.
const areaPath = `${linePath} L ${xFor(n - 1).toFixed(1)} ${(PAD_T + plotH).toFixed(1)} L ${xFor(0).toFixed(1)} ${(PAD_T + plotH).toFixed(1)} Z`;

// Biggest day annotation. Falls back to scanning the series if the
// server didn't tell us (e.g. partial backfill, gauge not populated).
// Biggest day annotation. ALWAYS computed from the displayed series,
// never from the server-rendered `biggestDayUnix` prop alone. The two
// sources race: the page server-renders biggestDayUnix from a Prom
// scalar cached for the ISR window (60-300 s) while the chart fetches
// /api/builder/<slug>/daily-series at hydration time and gets the
// fresh JSON straight from the harness. When a new biggest day rolls
// in between those two reads, the marker stops landing on the tallest
// bar (it points to the previous biggest, which is still in the
// series but no longer the max).
//
// The server prop is kept as a tiebreaker: if it falls inside the
// displayed series and the series is uniformly zero (cold start,
// never observed a fill), surface its UTC day so the marker still
// shows up. In every other case the series tells us which bar is the
// tallest, which is exactly what the marker is supposed to point at.
const biggestIdx = useMemo(() => {
if (biggestDayUnix && biggestDayUnix > 0) {
const found = data.points.findIndex(
(p) => Math.abs(p.day_unix - biggestDayUnix) < 86400,
);
if (found >= 0) return found;
}
let bestI = -1;
let bestV = 0;
for (let i = 0; i < data.points.length; i++) {
Expand All@@ -175,7 +182,14 @@ function ChartCanvas({
bestI = i;
}
}
return bestI;
if (bestI >= 0) return bestI;
if (biggestDayUnix && biggestDayUnix > 0) {
const found = data.points.findIndex(
(p) => Math.abs(p.day_unix - biggestDayUnix) < 86400,
);
if (found >= 0) return found;
}
return -1;
}, [data.points, biggestDayUnix]);

// Hover state. We track the index of the hovered bar (the bar a
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