fix(dashboards): keep DST fall-back range endpoints and resolve threshold axis from first series

Author: TheodoreSpeaks

apps/sim/lib/charts/annotations.test.ts

@@ -116,4 +116,28 @@ describe('chart annotations', () => {
       )
     ).toThrow('Use highlights and thresholds instead of markArea or markLine on the series')
   })
+
+  it('measures thresholds on the axes the first series is plotted on', () => {
+    const option = applyChartAnnotations(
+      {
+        xAxis: { type: 'time' },
+        yAxis: [{ type: 'category' }, { id: 'latency', type: 'value' }],
+        series: [{ type: 'line', yAxisIndex: 1 }],
+      },
+      { thresholds: [{ value: 5 }] },
+      palette
+    )
+    expect((option.series as Series[])[0].markLine).toMatchObject({ data: [{ yAxis: 5 }] })
+    expect(() =>
+      applyChartAnnotations(
+        {
+          xAxis: { type: 'time' },
+          yAxis: [{ type: 'value' }, { id: 'stage', type: 'category' }],
+          series: [{ type: 'line', yAxisId: 'stage' }],
+        },
+        { thresholds: [{ value: 5 }] },
+        palette
+      )
+    ).toThrow('Thresholds require a value axis')
+  })
 })

apps/sim/lib/charts/annotations.ts

@@ -27,17 +27,39 @@ export interface ChartAnnotations {
 
 const BAND_OPACITY = 0.08
 
-function firstAxis(axis: unknown): Record<string, unknown> {
-  return toRecord(Array.isArray(axis) ? axis[0] : axis)
+function firstSeries(option: Record<string, unknown>): Record<string, unknown> {
+  return toRecord(Array.isArray(option.series) ? option.series[0] : option.series)
 }
 
-/** The axis a threshold is measured on; ECharts defaults an unspecified yAxis to a value axis. */
+/** The axis the first series is plotted on, resolved through its `*AxisId` or `*AxisIndex`. */
+function seriesAxis(
+  option: Record<string, unknown>,
+  key: 'xAxis' | 'yAxis'
+): Record<string, unknown> {
+  const axes = Array.isArray(option[key]) ? (option[key] as unknown[]) : [option[key]]
+  const series = firstSeries(option)
+  const id = series[`${key}Id`]
+  if (id !== undefined) {
+    const axis = axes.find((candidate) => toRecord(candidate).id === id)
+    if (axis === undefined) throw new Error(`The first series references a missing ${key} "${id}"`)
+    return toRecord(axis)
+  }
+  const index = series[`${key}Index`] ?? 0
+  if (typeof index !== 'number' || (index > 0 && axes[index] === undefined))
+    throw new Error(`The first series references a missing ${key} at index ${String(index)}`)
+  return toRecord(axes[index])
+}
+
+/**
+ * The axis a threshold is measured on, among the axes the first series is plotted on; ECharts
+ * defaults an unspecified yAxis to a value axis.
+ */
 export function valueAxisKey(option: Record<string, unknown>): 'xAxis' | 'yAxis' {
   if (option.xAxis === undefined && option.yAxis === undefined)
     throw new Error('Thresholds require a value axis')
-  const y = firstAxis(option.yAxis)
+  const y = seriesAxis(option, 'yAxis')
   if (y.type === undefined || y.type === 'value' || y.type === 'log') return 'yAxis'
-  const x = firstAxis(option.xAxis)
+  const x = seriesAxis(option, 'xAxis')
   if (x.type === 'value' || x.type === 'log') return 'xAxis'
   throw new Error('Thresholds require a value axis')
 }
@@ -47,7 +69,7 @@ export function valueAxisKey(option: Record<string, unknown>): 'xAxis' | 'yAxis'
  * y axis is inverted (as horizontal bar charts usually are).
  */
 function verticalTop(option: Record<string, unknown>): 'start' | 'end' {
-  return firstAxis(option.yAxis).inverse === true ? 'start' : 'end'
+  return seriesAxis(option, 'yAxis').inverse === true ? 'start' : 'end'
 }
 
 /** A chart annotations can draw on: a first series with no hand-written marks to collide with. */

apps/sim/lib/dashboards/time.test.ts

@@ -2,6 +2,7 @@ import { describe, expect, it } from 'vitest'
 import {
   dashboardAxisFormatter,
   dashboardRangeFromCalendar,
+  dashboardRangeText,
   dashboardTimeLabel,
   dashboardZoomRange,
   parseDashboardCustomRange,
@@ -47,4 +48,13 @@ describe('dashboard time interactions', () => {
     expect(dashboardTimeLabel(stamp, 'America/Los_Angeles')).toContain('PDT')
     expect(dashboardTimeLabel('2026-12-20T02:30:00Z', 'America/Los_Angeles')).toContain('PST')
   })
+
+  it('keeps both ends of a range that repeats the same wall-clock minute across a DST fall-back', () => {
+    const text = dashboardRangeText(
+      { from: '2026-11-01T05:30:00.000Z', to: '2026-11-01T06:31:00.000Z' },
+      'America/New_York'
+    )
+    expect(text).toContain('01:30:00 EDT')
+    expect(text).toContain('01:30:59 EST')
+  })
 })

apps/sim/lib/dashboards/time.ts

@@ -89,6 +89,20 @@ export function dashboardRangeText(range: DashboardTimeRange, timeZone: string):
   const to = new Date(Date.parse(range.to) - 1)
   const fromLocal = zonedWallClock(from, timeZone)
   const toLocal = zonedWallClock(to, timeZone)
+  if (fromLocal === toLocal) {
+    // Same wall-clock minute (e.g. a DST fall-back repeat): formatRange would collapse both ends.
+    const exact = new Intl.DateTimeFormat('en-US', {
+      timeZone,
+      month: 'short',
+      day: 'numeric',
+      hour: '2-digit',
+      minute: '2-digit',
+      second: '2-digit',
+      hourCycle: 'h23',
+      timeZoneName: 'short',
+    })
+    return `${exact.format(from)} – ${exact.format(to)}`
+  }
   const sameDay = fromLocal.slice(0, 10) === toLocal.slice(0, 10)
   return new Intl.DateTimeFormat('en-US', {
     timeZone,