feat(studio): apply timezone picker to observability/reports charts (#45667)

## Problem

The dashboard's timezone picker (#45517) propagates to log timestamps
and the shared TimestampInfo component, but observability and reports
charts still render their X-axis labels, range labels, and tooltip
headers in the browser's local timezone. The result is jarring once a
user picks a non-local timezone: hover a chart and you get one tz, hover
a log row and you get another.

## Fix

Routes all display-side timestamp formatting in the chart layer through
the existing picker-aware helpers (\`useFormatDateTime\` /
\`formatDateTime\`) so chart UI matches the rest of the dashboard.

- **ComposedChart.utils** \`CustomTooltip\` (the hotspot — drives every
observability dashboard tooltip): reads the active timezone via
\`useTimezone\` for both the header label and the formatted timestamp.
- **AreaChart** / **BarChart**: introduce a \`formatChartDate\` helper
that honours each component's existing \`displayDateInUtc\` prop,
otherwise routes through the picker.
- **ChartBlock**: the two recharts \`labelFormatter\` arrows now close
over \`useFormatDateTime\`.
- **ChartHighlightActions**: range labels in the zoom dropdown migrated
to the same hook.

Intentionally untouched (must stay UTC):
- \`ChartHandler\` / \`ChartBlock\` \`startDate\`/\`endDate\` (API range
params, day boundary).
- \`ChartBlock.tsx:166\` explicit \`.utc()\` data-key normalisation.
- \`useFillTimeseriesSorted\` and friends (range math, no display).

## How to test

- Sign in. Open the avatar dropdown, pick a timezone different from your
browser local (e.g. Asia/Tokyo).
- Visit any project, then \`/project/<ref>/reports/database\` (or any
\`/observability/...\` page).
- Hover any chart series — the tooltip header should display the chosen
IANA name and times in that timezone.
- Click-drag a range on a chart to open the zoom dropdown — start/end
labels in the menu should also be in the chosen timezone.
- Switch back to "Auto detect" and confirm everything reverts to
browser-local.
- For an AreaChart/BarChart that uses \`displayDateInUtc\` (e.g. some
legacy reports), confirm those still render in UTC regardless of picker.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Refactor**
* Standardized date/time formatting across charts, tooltips, axis
labels, header/footer labels, and highlight range labels in Reports and
chart components.
* Switched to a shared, timezone-aware formatter that respects UTC
display mode or the selected picker/timezone, ensuring consistent,
human-readable timestamps throughout the UI.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/studio/components/interfaces/Reports/ReportBlock/ChartBlock.tsx

@@ -27,6 +27,7 @@ import {
   useProjectDailyStatsQuery,
 } from '@/data/analytics/project-daily-stats-query'
 import { METRICS } from '@/lib/constants/metrics'
+import { useFormatDateTime } from '@/lib/datetime'
 import { useDatabaseSelectorStateSnapshot } from '@/state/database-selector'
 import type { Dashboards } from '@/types'
 
@@ -72,6 +73,7 @@ export const ChartBlock = ({
   const [chartStyle, setChartStyle] = useState<string>(defaultChartStyle)
   const logScale = useMemo(() => defaultLogScale, [defaultLogScale])
   const [latestValue, setLatestValue] = useState<string | undefined>()
+  const formatChartDate = useFormatDateTime()
 
   const databaseIdentifier = state.selectedDatabaseId
 
@@ -316,7 +318,7 @@ export const ChartBlock = ({
                     <ChartTooltipContent
                       className="min-w-[200px]"
                       labelSuffix={isPercentage ? '%' : ''}
-                      labelFormatter={(x) => dayjs(x).format('DD MMM YYYY')}
+                      labelFormatter={(x) => formatChartDate(x as string | number, 'DD MMM YYYY')}
                     />
                   }
                 />
@@ -343,7 +345,7 @@ export const ChartBlock = ({
                   content={
                     <ChartTooltipContent
                       labelSuffix={chartData?.format === '%' ? '%' : ''}
-                      labelFormatter={(x) => dayjs(x).format('DD MMM YYYY')}
+                      labelFormatter={(x) => formatChartDate(x as string | number, 'DD MMM YYYY')}
                     />
                   }
                 />

apps/studio/components/ui/Charts/AreaChart.tsx

@@ -1,4 +1,3 @@
-import dayjs from 'dayjs'
 import { useState } from 'react'
 import { Area, AreaChart as RechartAreaChart, Tooltip, XAxis } from 'recharts'
 
@@ -8,6 +7,7 @@ import { numberFormatter, useChartSize } from './Charts.utils'
 import NoDataPlaceholder from './NoDataPlaceholder'
 import { useChartHoverState } from './useChartHoverState'
 import { CHART_COLORS, DateTimeFormats } from '@/components/ui/Charts/Charts.constants'
+import { formatDateTime, useFormatDateTime } from '@/lib/datetime'
 
 export interface AreaChartProps<D = Datum> extends CommonChartProps<D> {
   yAxisKey: string
@@ -40,12 +40,19 @@ const AreaChart = ({
   )
   const [focusDataIndex, setFocusDataIndex] = useState<number | null>(null)
 
-  const day = (value: number | string) => (displayDateInUtc ? dayjs(value).utc() : dayjs(value))
+  // When `displayDateInUtc` is set the chart explicitly wants UTC labels (used
+  // by views that display server time). Otherwise honour the user's selected
+  // timezone via the picker, which `useFormatDateTime` reads from context.
+  const formatPickerDate = useFormatDateTime()
+  const formatChartDate = (value: number | string) =>
+    displayDateInUtc
+      ? formatDateTime(value, { tz: 'UTC', format: customDateFormat })
+      : formatPickerDate(value, customDateFormat)
   const resolvedHighlightedLabel =
     (focusDataIndex !== null &&
       data &&
       data[focusDataIndex] !== undefined &&
-      day(data[focusDataIndex][xAxisKey]).format(customDateFormat)) ||
+      formatChartDate(data[focusDataIndex][xAxisKey])) ||
     highlightedLabel
 
   const resolvedHighlightedValue =
@@ -129,7 +136,7 @@ const AreaChart = ({
               syncId && syncTooltip && hoveredIndex !== null ? (
                 <div className="bg-black/90 text-white p-2 rounded-sm text-xs">
                   <div className="font-medium">
-                    {dayjs(data[hoveredIndex]?.[xAxisKey]).format(customDateFormat)}
+                    {formatChartDate(data[hoveredIndex]?.[xAxisKey] as number | string)}
                   </div>
                   <div>
                     {numberFormatter(Number(data[hoveredIndex]?.[yAxisKey]) || 0, valuePrecision)}
@@ -150,8 +157,8 @@ const AreaChart = ({
       </Container>
       {data && (
         <div className="text-foreground-lighter -mt-8 flex items-center justify-between text-xs">
-          <span>{dayjs(data[0][xAxisKey]).format(customDateFormat)}</span>
-          <span>{dayjs(data[data?.length - 1]?.[xAxisKey]).format(customDateFormat)}</span>
+          <span>{formatChartDate(data[0][xAxisKey] as number | string)}</span>
+          <span>{formatChartDate(data[data?.length - 1]?.[xAxisKey] as number | string)}</span>
         </div>
       )}
     </div>

apps/studio/components/ui/Charts/BarChart.tsx

@@ -1,4 +1,3 @@
-import dayjs from 'dayjs'
 import { ComponentProps, useMemo, useState } from 'react'
 import {
   Bar,
@@ -18,6 +17,7 @@ import { numberFormatter, useChartSize } from './Charts.utils'
 import NoDataPlaceholder from './NoDataPlaceholder'
 import { useChartHoverState } from './useChartHoverState'
 import { CHART_COLORS, DateTimeFormats } from '@/components/ui/Charts/Charts.constants'
+import { formatDateTime, useFormatDateTime } from '@/lib/datetime'
 
 export interface BarChartProps<D = Datum> extends CommonChartProps<D> {
   yAxisKey: string
@@ -83,7 +83,14 @@ function BarChart<D extends Datum = Datum>({
     width: 0,
   }
 
-  const day = (value: number | string) => (displayDateInUtc ? dayjs(value).utc() : dayjs(value))
+  // When `displayDateInUtc` is set the chart explicitly wants UTC labels.
+  // Otherwise honour the user's selected timezone via the picker, which
+  // `useFormatDateTime` reads from context.
+  const formatPickerDate = useFormatDateTime()
+  const formatChartDate = (value: number | string) =>
+    displayDateInUtc
+      ? formatDateTime(value, { tz: 'UTC', format: customDateFormat })
+      : formatPickerDate(value, customDateFormat)
 
   function getHeaderLabel() {
     if (!xAxisIsDate) {
@@ -94,7 +101,7 @@ function BarChart<D extends Datum = Datum>({
       (focusDataIndex !== null &&
         data &&
         data[focusDataIndex] !== undefined &&
-        day(data[focusDataIndex][xAxisKey]).format(customDateFormat)) ||
+        formatChartDate(data[focusDataIndex][xAxisKey] as number | string)) ||
       highlightedLabel
     )
   }
@@ -175,7 +182,7 @@ function BarChart<D extends Datum = Datum>({
               syncId && isHovered && isCurrentChart && hoveredIndex !== null ? (
                 <div className="bg-black/90 text-white p-2 rounded-sm text-xs">
                   <div className="font-medium">
-                    {dayjs(data[hoveredIndex]?.[xAxisKey]).format(customDateFormat)}
+                    {formatChartDate(data[hoveredIndex]?.[xAxisKey] as number | string)}
                   </div>
                   <div>
                     {numberFormatter(Number(data[hoveredIndex]?.[yAxisKey]) || 0, valuePrecision)}
@@ -209,11 +216,13 @@ function BarChart<D extends Datum = Datum>({
       {data && (
         <div className="text-foreground-lighter -mt-10 flex items-center justify-between text-[10px] font-mono">
           <span>
-            {xAxisIsDate ? day(data[0][xAxisKey]).format(customDateFormat) : data[0][xAxisKey]}
+            {xAxisIsDate
+              ? formatChartDate(data[0][xAxisKey] as number | string)
+              : data[0][xAxisKey]}
           </span>
           <span>
             {xAxisIsDate
-              ? day(data[data?.length - 1]?.[xAxisKey]).format(customDateFormat)
+              ? formatChartDate(data[data?.length - 1]?.[xAxisKey] as number | string)
               : data[data?.length - 1]?.[xAxisKey]}
           </span>
         </div>

apps/studio/components/ui/Charts/ChartHeader.tsx

@@ -1,5 +1,4 @@
 import { useParams } from 'common'
-import dayjs from 'dayjs'
 import {
   Activity,
   BarChartIcon,
@@ -15,6 +14,7 @@ import { InfoTooltip } from 'ui-patterns/info-tooltip'
 import { formatPercentage, numberFormatter } from './Charts.utils'
 import { useChartHoverState } from './useChartHoverState'
 import { ButtonTooltip } from '@/components/ui/ButtonTooltip'
+import { formatDateTime, useFormatDateTime } from '@/lib/datetime'
 import { formatBytes } from '@/lib/helpers'
 
 export interface ChartHeaderProps {
@@ -83,6 +83,10 @@ export const ChartHeader = ({
   const [localHighlightedValue, setLocalHighlightedValue] = useState(highlightedValue)
   const [localHighlightedLabel, setLocalHighlightedLabel] = useState(highlightedLabel)
 
+  // When `displayDateInUtc` is set the chart explicitly wants UTC labels.
+  // Otherwise honour the user's selected timezone via the picker.
+  const formatPickerDate = useFormatDateTime()
+
   const formatHighlightedValue = (value: any) => {
     if (typeof value !== 'number') {
       return value
@@ -146,11 +150,11 @@ export const ChartHeader = ({
         // Update highlighted label based on sync state
         let newLabel = highlightedLabel
         if (xAxisIsDate && activeDataPoint[xAxisKey]) {
-          const day = (value: number | string) =>
-            displayDateInUtc ? dayjs(value).utc() : dayjs(value)
-          newLabel = day(activeDataPoint[xAxisKey]).format(
-            customDateFormat || 'YYYY-MM-DD HH:mm:ss'
-          )
+          const value = activeDataPoint[xAxisKey] as number | string
+          const fmt = customDateFormat || 'YYYY-MM-DD HH:mm:ss'
+          newLabel = displayDateInUtc
+            ? formatDateTime(value, { tz: 'UTC', format: fmt })
+            : formatPickerDate(value, fmt)
         } else if (activeDataPoint[xAxisKey]) {
           newLabel = activeDataPoint[xAxisKey]
         }
@@ -174,6 +178,7 @@ export const ChartHeader = ({
     highlightedValue,
     highlightedLabel,
     attributes,
+    formatPickerDate,
   ])
 
   const chartTitle = (

apps/studio/components/ui/Charts/ChartHighlightActions.tsx

@@ -12,6 +12,7 @@ import {
 } from 'ui'
 
 import { ChartHighlight } from './useChartHighlight'
+import { useFormatDateTime } from '@/lib/datetime'
 
 export type UpdateDateRange = (from: string, to: string) => void
 
@@ -44,6 +45,7 @@ export const ChartHighlightActions = ({
 }) => {
   const { left: selectedRangeStart, right: selectedRangeEnd, clearHighlight } = chartHighlight ?? {}
   const [isOpen, setIsOpen] = useState(!!chartHighlight?.popoverPosition)
+  const formatChartDate = useFormatDateTime()
 
   useEffect(() => {
     setIsOpen(!!chartHighlight?.popoverPosition && selectedRangeStart !== selectedRangeEnd)
@@ -90,9 +92,9 @@ export const ChartHighlightActions = ({
       />
       <DropdownMenuContent className="flex flex-col gap-1 p-1 w-fit text-left">
         <DropdownMenuLabel className="flex items-center justify-center text-foreground-light font-mono gap-x-2 text-xs">
-          <span>{dayjs(selectedRangeStart).format('MMM D, H:mm')}</span>
+          <span>{formatChartDate(selectedRangeStart!, 'MMM D, H:mm')}</span>
           <ArrowRight size={10} />
-          <span>{dayjs(selectedRangeEnd).format('MMM D, H:mm')}</span>
+          <span>{formatChartDate(selectedRangeEnd!, 'MMM D, H:mm')}</span>
         </DropdownMenuLabel>
         <DropdownMenuSeparator className="my-0" />
         {allActions.map((action) => {

apps/studio/components/ui/Charts/ComposedChart.tsx

@@ -1,4 +1,3 @@
-import dayjs from 'dayjs'
 import { useTheme } from 'next-themes'
 import { ComponentProps, useEffect, useMemo, useState } from 'react'
 import {
@@ -44,6 +43,7 @@ import {
 import NoDataPlaceholder from './NoDataPlaceholder'
 import { ChartHighlight } from './useChartHighlight'
 import { useChartHoverState } from './useChartHoverState'
+import { formatDateTime, useFormatDateTime } from '@/lib/datetime'
 import { formatBytes } from '@/lib/helpers'
 
 export interface ComposedChartProps<D = Datum> extends CommonChartProps<D> {
@@ -155,7 +155,13 @@ export function ComposedChart({
 
   const { Container } = useChartSize(size)
 
-  const day = (value: number | string) => (displayDateInUtc ? dayjs(value).utc() : dayjs(value))
+  // When `displayDateInUtc` is set the chart explicitly wants UTC labels.
+  // Otherwise honour the user's selected timezone via the picker.
+  const formatPickerDate = useFormatDateTime()
+  const formatChartDate = (value: number | string) =>
+    displayDateInUtc
+      ? formatDateTime(value, { tz: 'UTC', format: customDateFormat })
+      : formatPickerDate(value, customDateFormat)
 
   const formatTimestamp = (ts: unknown) => {
     if (typeof ts !== 'number' && typeof ts !== 'string') {
@@ -163,10 +169,11 @@ export function ComposedChart({
     }
 
     if (typeof ts === 'number' && ts > 1e14) {
-      return day(ts / 1000).format(customDateFormat)
+      // Microsecond timestamp; convert to milliseconds before formatting.
+      return formatChartDate(ts / 1000)
     }
 
-    return day(ts).format(customDateFormat)
+    return formatChartDate(ts)
   }
 
   const _XAxisProps = XAxisProps || {

apps/studio/components/ui/Charts/ComposedChart.utils.tsx

@@ -1,12 +1,11 @@
 'use client'
 
-import dayjs from 'dayjs'
 import { useState } from 'react'
 import { cn, Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from 'ui'
 
 import { CHART_COLORS, DateTimeFormats } from './Charts.constants'
 import { formatPercentage, numberFormatter } from './Charts.utils'
-import { guessLocalTimezone } from '@/lib/dayjs'
+import { useFormatDateTime, useTimezone } from '@/lib/datetime'
 import { formatBytes } from '@/lib/helpers'
 
 export interface ReportAttributes {
@@ -154,6 +153,8 @@ export const CustomTooltip = ({
   showTotal,
   isActiveHoveredChart,
 }: TooltipProps) => {
+  const formatDateTime = useFormatDateTime()
+  const { timezone } = useTimezone()
   if (active && payload && payload.length) {
     /**
      * Depending on the data source, the timestamp key could be 'timestamp' or 'period_start'
@@ -194,7 +195,7 @@ export const CustomTooltip = ({
       ...(maxValueAttribute?.attribute ? [maxValueAttribute.attribute] : []),
     ]
 
-    const localTimeZone = guessLocalTimezone()
+    const localTimeZone = timezone
 
     const rawPayload = payload.map((entry: any) => ({
       ...entry,
@@ -256,7 +257,7 @@ export const CustomTooltip = ({
         )}
       >
         <p className="text-foreground-light text-xs">{localTimeZone}</p>
-        <p className="font-medium">{dayjs(timestamp).format(DateTimeFormats.FULL_SECONDS)}</p>
+        <p className="font-medium">{formatDateTime(timestamp, DateTimeFormats.FULL_SECONDS)}</p>
         <div className="grid gap-0">
           {[...payload].reverse().map((entry: any, index: number) => (
             <LabelItem key={`${entry.name}-${index}`} entry={entry} />

apps/studio/components/ui/Charts/StackedBarChart.tsx

@@ -1,4 +1,3 @@
-import dayjs from 'dayjs'
 import { useState } from 'react'
 import { Bar, BarChart, Cell, Legend, Tooltip, XAxis } from 'recharts'
 
@@ -11,15 +10,10 @@ import {
   ValidStackColor,
 } from './Charts.constants'
 import type { CommonChartProps } from './Charts.types'
-import {
-  numberFormatter,
-  precisionFormatter,
-  timestampFormatter,
-  useChartSize,
-  useStacked,
-} from './Charts.utils'
+import { numberFormatter, precisionFormatter, useChartSize, useStacked } from './Charts.utils'
 import NoDataPlaceholder from './NoDataPlaceholder'
 import { useChartHoverState } from './useChartHoverState'
+import { formatDateTime, useFormatDateTime } from '@/lib/datetime'
 
 interface Props extends CommonChartProps<any> {
   xAxisKey: string
@@ -69,12 +63,19 @@ const StackedBarChart: React.FC<Props> = ({
   })
   const [focusDataIndex, setFocusDataIndex] = useState<number | null>(null)
 
-  const day = (value: number | string) => (displayDateInUtc ? dayjs(value).utc() : dayjs(value))
+  // When `displayDateInUtc` is set the chart explicitly wants UTC labels.
+  // Otherwise honour the user's selected timezone via the picker.
+  const formatPickerDate = useFormatDateTime()
+  const formatChartDate = (value: number | string) =>
+    displayDateInUtc
+      ? formatDateTime(value, { tz: 'UTC', format: customDateFormat })
+      : formatPickerDate(value, customDateFormat)
+
   const resolvedHighlightedLabel =
     (focusDataIndex !== null &&
       data &&
       data[focusDataIndex] !== undefined &&
-      day(data[focusDataIndex][xAxisKey]).format(customDateFormat)) ||
+      formatChartDate(data[focusDataIndex][xAxisKey])) ||
     highlightedLabel
 
   const resolvedHighlightedValue =
@@ -179,9 +180,7 @@ const StackedBarChart: React.FC<Props> = ({
           ))}
           <Tooltip
             labelFormatter={
-              xAxisFormatAsDate
-                ? (label) => timestampFormatter(label, customDateFormat, displayDateInUtc)
-                : undefined
+              xAxisFormatAsDate ? (label) => formatChartDate(label as number | string) : undefined
             }
             formatter={(value, name, props) => {
               const suffix = format || ''
@@ -209,19 +208,9 @@ const StackedBarChart: React.FC<Props> = ({
       </Container>
       {stackedData && stackedData[0] && (
         <div className="text-foreground-lighter -mt-5 flex items-center justify-between text-xs">
+          <span>{formatChartDate(stackedData[0][xAxisKey] as number | string)}</span>
           <span>
-            {timestampFormatter(
-              stackedData[0][xAxisKey] as string,
-              customDateFormat,
-              displayDateInUtc
-            )}
-          </span>
-          <span>
-            {timestampFormatter(
-              stackedData[stackedData?.length - 1][xAxisKey] as string,
-              customDateFormat,
-              displayDateInUtc
-            )}
+            {formatChartDate(stackedData[stackedData?.length - 1][xAxisKey] as number | string)}
           </span>
         </div>
       )}