From 383f51eb4881dfb4c41eb5d644a8505ba3f60ad9 Mon Sep 17 00:00:00 2001
From: John Coffey <johnellis@linux.com>
Date: Mon, 5 Oct 2026 15:06:14 -0700
Subject: [PATCH] Dashboard charts: drag across one to zoom

Admin UX roadmap item 15, "charts you can zoom". Dragging across a
trend chart narrows every panel to that window; a Zoom chip beside the
period keys shows it, and clicking the chip goes back to the preset.

- History is sampled hourly unless set otherwise, so a zoomed window
  gets a slice per hour (3 to 60) and is never under three hours; a
  shorter sweep widens around its middle.
- Only the preset is saved, so a reload is back at it rather than in an
  old window.
- The slice under the pointer comes from its position on the plot, not
  from recharts' hover state, which runs a frame behind and made a
  quick sweep end where it began.
- Charts are plotted by slice rather than by label, so two slices that
  print alike stay apart.

3 new English strings; no other catalogues yet.
---
 .../dashboard/components/BridgeControls.tsx   |  28 ++++-
 .../dashboard/components/TrendChart.tsx       |  89 +++++++++++--
 src/features/dashboard/helpers.ts             |  56 ++++++++-
 .../dashboard/stores/dashboardStore.ts        |  18 ++-
 src/features/dashboard/types/metrics.ts       |   4 +
 src/features/dashboard/zoom.test.ts           | 119 ++++++++++++++++++
 src/i18n/en.json                              |   5 +-
 7 files changed, 304 insertions(+), 15 deletions(-)
 create mode 100644 src/features/dashboard/zoom.test.ts

diff --git a/src/features/dashboard/components/BridgeControls.tsx b/src/features/dashboard/components/BridgeControls.tsx
index 3463a45..4939f9d 100644
--- a/src/features/dashboard/components/BridgeControls.tsx
+++ b/src/features/dashboard/components/BridgeControls.tsx
@@ -7,7 +7,7 @@
 import { useEffect, useState, type ReactNode } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Link } from 'react-router-dom';
-import { Gauge as GaugeIcon, RefreshCw } from 'lucide-react';
+import { Gauge as GaugeIcon, RefreshCw, X } from 'lucide-react';
 import type { Dashboard } from '../types/schema';
 import { cn } from '@/lib/utils';
 import { AUTO_REFRESH, useDashboardStore, type AutoRefresh } from '../stores/dashboardStore';
@@ -71,6 +71,8 @@ export function PeriodSwitch({ loading = false }: { loading?: boolean }) {
   const { t } = useTranslation();
   const period = useDashboardStore((s) => s.period);
   const setPreset = useDashboardStore((s) => s.setPreset);
+  const zoomedFrom = useDashboardStore((s) => s.zoomedFrom);
+  const resetZoom = useDashboardStore((s) => s.resetZoom);
   const every = useDashboardStore((s) => s.autoRefresh);
   const setEvery = useDashboardStore((s) => s.setAutoRefresh);
   const onRefresh = useDashboardStore((s) => s.bump);
@@ -103,6 +105,21 @@ export function PeriodSwitch({ loading = false }: { loading?: boolean }) {
           </button>
         ))}
       </div>
+      {/* inbuxa: zoomed in from a chart, the window shown, and the way back. */}
+      {zoomedFrom && period.kind === 'custom' && (
+        <button
+          type="button"
+          onClick={resetZoom}
+          title={t('cc.zoomReset', 'Back to {{period}}', {
+            period: zoomedFrom.kind === 'preset' ? zoomedFrom.preset.toUpperCase() : '',
+          })}
+          className="inline-flex items-center gap-1.5 rounded-lg border border-primary/50 bg-primary/10 px-2.5 py-1 font-mono text-[11px] font-semibold tracking-wider text-foreground transition-colors hover:bg-primary/20"
+        >
+          <span className="uppercase text-muted-foreground">{t('cc.zoomed', 'Zoom')}</span>
+          {formatZoom(period.from, period.to)}
+          <X className="h-3 w-3 text-muted-foreground" aria-hidden />
+        </button>
+      )}
       <div className="flex items-center rounded-lg border bg-background/60">
         <button
           type="button"
@@ -209,3 +226,12 @@ export function DashNav({
     </nav>
   );
 }
+
+/** inbuxa: a zoomed window, short: "5 Oct 14:00 – 17:00", or both dates when it spans days. */
+function formatZoom(from: Date, to: Date): string {
+  const day = (d: Date) => d.toLocaleDateString(undefined, { day: 'numeric', month: 'short' });
+  const time = (d: Date) => d.toLocaleTimeString(undefined, { hour: '2-digit', minute: '2-digit' });
+  return day(from) === day(to)
+    ? `${day(from)} ${time(from)} – ${time(to)}`
+    : `${day(from)} ${time(from)} – ${day(to)} ${time(to)}`;
+}
diff --git a/src/features/dashboard/components/TrendChart.tsx b/src/features/dashboard/components/TrendChart.tsx
index 482030c..6dcefb7 100644
--- a/src/features/dashboard/components/TrendChart.tsx
+++ b/src/features/dashboard/components/TrendChart.tsx
@@ -29,7 +29,10 @@ import {
   formatValue,
   getBucketCount,
   seriesBucketValue,
+  sliceAt,
+  zoomWindow,
 } from '../helpers';
+import { useDashboardStore } from '../stores/dashboardStore';
 import { LATENCIES, summarize } from '../commandCenter';
 import { hrefFor, linkForMetrics } from '../links';
 import { usePermissions } from '@/hooks/usePermissions';
@@ -74,11 +77,16 @@ export function TrendChart({ chart, samples, window: { from, to }, period, class
   const format = chart.valueFormat ?? 'number';
   const timing = format === 'duration';
   const buckets = getBucketCount(period);
+  const zoomTo = useDashboardStore((s) => s.zoomTo);
+  // Dragging across the chart: the slices it started and is now over.
+  const [drag, setDrag] = useState<{ a: number; b: number } | null>(null);
+  const canZoom = zoomWindow(from, to, buckets, 0, 1) !== null;
 
   const data = useMemo(() => {
     const slices = bucketize(samples, from, to, buckets);
     return bucketTimestamps(from, to, buckets).map((ts, i) => {
-      const point: Record<string, number | string | null> = { tick: formatTimeTick(ts, period) };
+      // Charted by slice, so two slices that print alike ("14:00" on two days) stay apart.
+      const point: Record<string, number | string | null> = { i, tick: formatTimeTick(ts, period) };
       for (const s of chart.series) point[s.label] = seriesBucketValue(s, slices[i]) ?? (timing ? null : 0);
       return point;
     });
@@ -90,10 +98,10 @@ export function TrendChart({ chart, samples, window: { from, to }, period, class
   const peak = useMemo(() => {
     if (timing || chart.kind === 'bar' || chart.series.length === 0) return null;
     const keys = chart.stacked ? chart.series.map((s) => s.label) : [chart.series[0].label];
-    let best: { tick: string; v: number } | null = null;
+    let best: { i: number; v: number } | null = null;
     for (const p of data) {
       const v = keys.reduce((sum, k) => sum + Number(p[k] ?? 0), 0);
-      if (v > 0 && (!best || v > best.v)) best = { tick: String(p.tick), v };
+      if (v > 0 && (!best || v > best.v)) best = { i: Number(p.i), v };
     }
     return best;
   }, [data, chart.series, chart.stacked, chart.kind, timing]);
@@ -105,7 +113,51 @@ export function TrendChart({ chart, samples, window: { from, to }, period, class
   const href = link && canViewObject(link.viewName) ? hrefFor(link) : null;
   const fmt = (v: number) => formatValue(v, format);
 
-  const common = { data, width, height: HEIGHT, margin: { top: 16, right: 24, left: 0, bottom: 0 } };
+  const tickAt = (i: unknown) => String(data[Number(i)]?.tick ?? '');
+  // Dragging is read off the pointer against the plot area (the chart's grid),
+  // not off recharts' hover state, which runs a frame behind: a quick sweep
+  // would end on the slice it started from.
+  const band = chart.kind === 'bar';
+  const sliceAtPointer = (clientX: number) => {
+    const plot = ref.current?.querySelector('.recharts-cartesian-grid')?.getBoundingClientRect();
+    return plot ? sliceAt(clientX, plot.left, plot.right, buckets, band) : null;
+  };
+  const dragRef = useRef<{ a: number; b: number } | null>(null);
+  const setDragBoth = (d: { a: number; b: number } | null) => {
+    dragRef.current = d;
+    setDrag(d);
+  };
+  const zoomHandlers = canZoom
+    ? {
+        onMouseDown: (e: React.MouseEvent) => {
+          if (e.button !== 0) return;
+          const i = sliceAtPointer(e.clientX);
+          if (i !== null) setDragBoth({ a: i, b: i });
+        },
+        onMouseMove: (e: React.MouseEvent) => {
+          const d = dragRef.current;
+          const i = d ? sliceAtPointer(e.clientX) : null;
+          if (d && i !== null && i !== d.b) setDragBoth({ a: d.a, b: i });
+        },
+        onMouseUp: (e: React.MouseEvent) => {
+          const d = dragRef.current;
+          const end = d ? (sliceAtPointer(e.clientX) ?? d.b) : null;
+          // A click isn't a drag: only a sweep over two slices or more zooms.
+          if (d && end !== null && d.a !== end) {
+            const w = zoomWindow(from, to, buckets, d.a, end);
+            if (w) zoomTo(w.from, w.to);
+          }
+          setDragBoth(null);
+        },
+        onMouseLeave: () => setDragBoth(null),
+      }
+    : {};
+  const common = {
+    data,
+    width,
+    height: HEIGHT,
+    margin: { top: 16, right: 24, left: 0, bottom: 0 },
+  };
   const chrome = (
     <>
       <defs>
@@ -117,7 +169,7 @@ export function TrendChart({ chart, samples, window: { from, to }, period, class
         ))}
       </defs>
       <CartesianGrid vertical={false} stroke="var(--border)" />
-      <XAxis dataKey="tick" tick={AXIS} tickLine={false} axisLine={false} minTickGap={28} />
+      <XAxis dataKey="i" tick={AXIS} tickLine={false} axisLine={false} minTickGap={28} tickFormatter={tickAt} />
       <YAxis tick={AXIS} tickLine={false} axisLine={false} width={56} tickFormatter={fmt} allowDecimals={timing} />
       {zones && (
         <>
@@ -142,7 +194,7 @@ export function TrendChart({ chart, samples, window: { from, to }, period, class
         content={({ active, payload, label }) =>
           active && payload?.length ? (
             <div className="rounded-lg border bg-popover px-3 py-2 font-mono text-xs shadow-md">
-              <div className="mb-1 text-muted-foreground">{label}</div>
+              <div className="mb-1 text-muted-foreground">{tickAt(label)}</div>
               {payload.map((p) => (
                 <div key={String(p.dataKey)} className="flex items-center gap-2">
                   <span className="h-2 w-2 rounded-full" style={{ background: p.color }} />
@@ -156,9 +208,19 @@ export function TrendChart({ chart, samples, window: { from, to }, period, class
           ) : null
         }
       />
+      {drag && drag.a !== drag.b && (
+        <ReferenceArea
+          x1={Math.min(drag.a, drag.b)}
+          x2={Math.max(drag.a, drag.b)}
+          fill="var(--primary)"
+          fillOpacity={0.12}
+          stroke="var(--primary)"
+          strokeOpacity={0.5}
+        />
+      )}
       {peak && (
         <ReferenceDot
-          x={peak.tick}
+          x={peak.i}
           y={peak.v}
           r={4}
           fill="var(--card)"
@@ -245,9 +307,20 @@ export function TrendChart({ chart, samples, window: { from, to }, period, class
             {timing && <span className="text-[10px] uppercase text-muted-foreground">{t('cc.avg', 'avg')}</span>}
           </span>
         ))}
+        {canZoom && (
+          <span className="ml-auto self-center font-mono text-[10px] uppercase tracking-wider text-muted-foreground/70">
+            {t('cc.dragToZoom', 'Drag to zoom')}
+          </span>
+        )}
         {chart.description && <span className="basis-full text-xs text-muted-foreground">{chart.description}</span>}
       </div>
-      <div ref={ref} style={{ height: HEIGHT }}>
+      <div
+        ref={ref}
+        // A press to drag focuses the chart; keep the ring for the keyboard only.
+        className="[&_.recharts-surface:focus:not(:focus-visible)]:outline-none"
+        style={{ height: HEIGHT, ...(canZoom ? { cursor: 'crosshair', userSelect: 'none' } : {}) }}
+        {...zoomHandlers}
+      >
         {width > 0 && (
           <Kind {...common}>
             {chrome}
diff --git a/src/features/dashboard/helpers.ts b/src/features/dashboard/helpers.ts
index 6efaf2e..0e63143 100644
--- a/src/features/dashboard/helpers.ts
+++ b/src/features/dashboard/helpers.ts
@@ -9,7 +9,14 @@
 
 import type { Metric, MetricId, Period } from './types/metrics';
 import type { Card, Series, MetricFormat, Aggregate } from './types/schema';
-import { PRESET_MS, BUCKET_CONFIG, CUSTOM_BUCKET_COUNT, SPARKLINE_BUCKET_COUNT } from './types/metrics';
+import {
+  PRESET_MS,
+  BUCKET_CONFIG,
+  CUSTOM_BUCKET_COUNT,
+  HOUR_MS,
+  MIN_ZOOM_MS,
+  SPARKLINE_BUCKET_COUNT,
+} from './types/metrics';
 
 export function metricToScalar(m: Metric): number {
   if (m['@type'] === 'Histogram') {
@@ -82,7 +89,11 @@ export function periodKey(p: Period): string {
 }
 
 export function getBucketCount(p: Period): number {
-  if (p.kind === 'custom') return CUSTOM_BUCKET_COUNT;
+  if (p.kind === 'custom') {
+    // inbuxa: a slice per hour of the window, as history is sampled hourly.
+    const hours = Math.round((p.to.getTime() - p.from.getTime()) / HOUR_MS);
+    return Math.min(CUSTOM_BUCKET_COUNT, Math.max(MIN_ZOOM_MS / HOUR_MS, hours));
+  }
   return BUCKET_CONFIG[p.preset];
 }
 
@@ -291,3 +302,44 @@ export function collectLiveMetricIds(cards: Card[] | undefined): Set<MetricId> {
   }
   return ids;
 }
+
+/**
+ * inbuxa: the window a drag across slices `a` to `b` of a chart zooms to: from
+ * the start of the first slice to the end of the last. A window under three
+ * hours widens around its middle, staying inside the chart's own. Null when
+ * the chart's window is already that narrow, so there's nothing to zoom into.
+ */
+export function zoomWindow(
+  from: Date,
+  to: Date,
+  buckets: number,
+  a: number,
+  b: number,
+): { from: Date; to: Date } | null {
+  const start = from.getTime();
+  const end = to.getTime();
+  if (end - start <= MIN_ZOOM_MS || buckets <= 0) return null;
+  const width = (end - start) / buckets;
+  const lo = Math.max(0, Math.min(a, b));
+  const hi = Math.min(buckets - 1, Math.max(a, b));
+  let zFrom = start + lo * width;
+  let zTo = start + (hi + 1) * width;
+  if (zTo - zFrom < MIN_ZOOM_MS) {
+    const mid = (zFrom + zTo) / 2;
+    zFrom = Math.max(start, Math.min(end - MIN_ZOOM_MS, mid - MIN_ZOOM_MS / 2));
+    zTo = zFrom + MIN_ZOOM_MS;
+  }
+  return { from: new Date(Math.round(zFrom)), to: new Date(Math.round(zTo)) };
+}
+
+/**
+ * inbuxa: which of `buckets` slices a pointer at `x` is over, on a plot from
+ * `left` to `right`. Lines and areas put the slices on points, first at the
+ * left edge and last at the right; bars put each in a band of its own.
+ */
+export function sliceAt(x: number, left: number, right: number, buckets: number, band: boolean): number | null {
+  if (buckets <= 0 || right <= left) return null;
+  const f = Math.min(1, Math.max(0, (x - left) / (right - left)));
+  const i = band ? Math.floor(f * buckets) : Math.round(f * (buckets - 1));
+  return Math.min(buckets - 1, i);
+}
diff --git a/src/features/dashboard/stores/dashboardStore.ts b/src/features/dashboard/stores/dashboardStore.ts
index 93adf11..5ff1bba 100644
--- a/src/features/dashboard/stores/dashboardStore.ts
+++ b/src/features/dashboard/stores/dashboardStore.ts
@@ -18,6 +18,14 @@ interface DashboardState {
   period: Period;
   setPeriod: (period: Period) => void;
   setPreset: (preset: PresetKey) => void;
+  /**
+   * inbuxa: the period a chart was zoomed from, while zoomed. Zooming makes the
+   * period a custom window; only this one is remembered, so a reload is back
+   * at the preset rather than in an old window.
+   */
+  zoomedFrom: Period | null;
+  zoomTo: (from: Date, to: Date) => void;
+  resetZoom: () => void;
   /** INBUXA: minutes between automatic refreshes of the dashboards; 0 is off. */
   autoRefresh: AutoRefresh;
   setAutoRefresh: (minutes: AutoRefresh) => void;
@@ -31,8 +39,12 @@ export const useDashboardStore = create<DashboardState>()(
     (set) => ({
       period: { kind: 'preset', preset: '24h' } as Period,
 
-      setPeriod: (period) => set({ period }),
-      setPreset: (preset) => set({ period: { kind: 'preset', preset } }),
+      setPeriod: (period) => set({ period, zoomedFrom: null }),
+      setPreset: (preset) => set({ period: { kind: 'preset', preset }, zoomedFrom: null }),
+      zoomedFrom: null,
+      zoomTo: (from, to) =>
+        set((s) => ({ period: { kind: 'custom', from, to }, zoomedFrom: s.zoomedFrom ?? s.period })),
+      resetZoom: () => set((s) => (s.zoomedFrom ? { period: s.zoomedFrom, zoomedFrom: null } : {})),
       autoRefresh: 5,
       setAutoRefresh: (autoRefresh) => set({ autoRefresh }),
       tick: 0,
@@ -40,7 +52,7 @@ export const useDashboardStore = create<DashboardState>()(
     }),
     {
       name: 'dashboard.period',
-      partialize: (state) => ({ period: state.period, autoRefresh: state.autoRefresh }),
+      partialize: (state) => ({ period: state.zoomedFrom ?? state.period, autoRefresh: state.autoRefresh }),
     },
   ),
 );
diff --git a/src/features/dashboard/types/metrics.ts b/src/features/dashboard/types/metrics.ts
index 0495a80..4caee11 100644
--- a/src/features/dashboard/types/metrics.ts
+++ b/src/features/dashboard/types/metrics.ts
@@ -49,4 +49,8 @@ export const BUCKET_CONFIG: Record<PresetKey, number> = {
 };
 
 export const CUSTOM_BUCKET_COUNT = 60;
+// inbuxa: history is sampled hourly unless set otherwise (`metricsCollectionInterval`),
+// so a zoomed window gets a slice per hour, 3 to 60 of them, and is never under 3 hours.
+export const HOUR_MS = 3_600_000;
+export const MIN_ZOOM_MS = 3 * HOUR_MS;
 export const SPARKLINE_BUCKET_COUNT = 20;
diff --git a/src/features/dashboard/zoom.test.ts b/src/features/dashboard/zoom.test.ts
new file mode 100644
index 0000000..d04caa2
--- /dev/null
+++ b/src/features/dashboard/zoom.test.ts
@@ -0,0 +1,119 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { beforeAll, beforeEach, describe, expect, it } from 'vitest';
+import { createJSONStorage } from 'zustand/middleware';
+import { getBucketCount, sliceAt, zoomWindow } from './helpers';
+import { useDashboardStore } from './stores/dashboardStore';
+
+const HOUR = 3_600_000;
+const FROM = new Date('2026-10-05T00:00:00Z');
+const at = (h: number) => new Date(FROM.getTime() + h * HOUR);
+
+describe('zoomWindow', () => {
+  it('runs from the start of the first slice to the end of the last, either way round', () => {
+    // 24 h in 48 slices of 30 min: slices 20 to 31 are 10:00 to 16:00.
+    expect(zoomWindow(FROM, at(24), 48, 20, 31)).toEqual({ from: at(10), to: at(16) });
+    expect(zoomWindow(FROM, at(24), 48, 31, 20)).toEqual({ from: at(10), to: at(16) });
+  });
+
+  it('widens a window under three hours around its middle', () => {
+    // Slices 20 and 21: 10:00 to 11:00, widened to 09:00 to 12:00.
+    expect(zoomWindow(FROM, at(24), 48, 20, 21)).toEqual({ from: at(9), to: at(12) });
+  });
+
+  it('keeps a widened window inside the chart', () => {
+    expect(zoomWindow(FROM, at(24), 48, 0, 1)).toEqual({ from: at(0), to: at(3) });
+    expect(zoomWindow(FROM, at(24), 48, 46, 47)).toEqual({ from: at(21), to: at(24) });
+  });
+
+  it('has nothing to zoom into once the chart is three hours or less', () => {
+    expect(zoomWindow(FROM, at(3), 3, 0, 2)).toBeNull();
+  });
+});
+
+describe('sliceAt', () => {
+  // A plot from x=100 to x=500, 5 slices.
+  it('puts line and area slices on points, edge to edge', () => {
+    expect(sliceAt(100, 100, 500, 5, false)).toBe(0);
+    expect(sliceAt(300, 100, 500, 5, false)).toBe(2);
+    expect(sliceAt(500, 100, 500, 5, false)).toBe(4);
+    expect(sliceAt(160, 100, 500, 5, false)).toBe(1);
+  });
+
+  it('puts bar slices in bands', () => {
+    expect(sliceAt(100, 100, 500, 5, true)).toBe(0);
+    expect(sliceAt(179, 100, 500, 5, true)).toBe(0);
+    expect(sliceAt(181, 100, 500, 5, true)).toBe(1);
+    expect(sliceAt(500, 100, 500, 5, true)).toBe(4);
+  });
+
+  it('holds a pointer past either edge to the end slice', () => {
+    expect(sliceAt(20, 100, 500, 5, false)).toBe(0);
+    expect(sliceAt(900, 100, 500, 5, true)).toBe(4);
+  });
+
+  it('has no slice on an empty plot', () => {
+    expect(sliceAt(300, 100, 100, 5, false)).toBeNull();
+    expect(sliceAt(300, 100, 500, 0, false)).toBeNull();
+  });
+});
+
+describe('getBucketCount for a zoomed window', () => {
+  const custom = (h: number) => ({ kind: 'custom' as const, from: FROM, to: at(h) });
+
+  it('gives a slice per hour', () => {
+    expect(getBucketCount(custom(6))).toBe(6);
+    expect(getBucketCount(custom(40))).toBe(40);
+  });
+
+  it('keeps between 3 and 60 slices', () => {
+    expect(getBucketCount(custom(2))).toBe(3);
+    expect(getBucketCount(custom(24 * 20))).toBe(60);
+  });
+});
+
+describe('zooming the dashboard period', () => {
+  // In memory: Node's own `localStorage` global, empty without a storage file, hides happy-dom's.
+  const saved = new Map<string, string>();
+  beforeAll(() =>
+    useDashboardStore.persist.setOptions({
+      storage: createJSONStorage(() => ({
+        getItem: (k) => saved.get(k) ?? null,
+        setItem: (k, v) => void saved.set(k, v),
+        removeItem: (k) => void saved.delete(k),
+      })),
+    }),
+  );
+  beforeEach(() => useDashboardStore.getState().setPreset('7d'));
+
+  it('remembers the preset it zoomed from, and goes back to it', () => {
+    useDashboardStore.getState().zoomTo(at(10), at(16));
+    expect(useDashboardStore.getState().period).toEqual({ kind: 'custom', from: at(10), to: at(16) });
+    expect(useDashboardStore.getState().zoomedFrom).toEqual({ kind: 'preset', preset: '7d' });
+
+    // Zooming again from inside a zoom still goes back to the preset.
+    useDashboardStore.getState().zoomTo(at(11), at(14));
+    expect(useDashboardStore.getState().zoomedFrom).toEqual({ kind: 'preset', preset: '7d' });
+
+    useDashboardStore.getState().resetZoom();
+    expect(useDashboardStore.getState().period).toEqual({ kind: 'preset', preset: '7d' });
+    expect(useDashboardStore.getState().zoomedFrom).toBeNull();
+  });
+
+  it('ends the zoom when a preset is picked', () => {
+    useDashboardStore.getState().zoomTo(at(10), at(16));
+    useDashboardStore.getState().setPreset('30d');
+    expect(useDashboardStore.getState().period).toEqual({ kind: 'preset', preset: '30d' });
+    expect(useDashboardStore.getState().zoomedFrom).toBeNull();
+  });
+
+  it('saves the preset, not the zoomed window', () => {
+    useDashboardStore.getState().zoomTo(at(10), at(16));
+    const stored = JSON.parse(saved.get('dashboard.period') ?? '{}');
+    expect(stored.state.period).toEqual({ kind: 'preset', preset: '7d' });
+  });
+});
diff --git a/src/i18n/en.json b/src/i18n/en.json
index 5459f9e..8ac449f 100644
--- a/src/i18n/en.json
+++ b/src/i18n/en.json
@@ -1951,7 +1951,10 @@
     },
     "now": "now",
     "avgZone": "average · {{zone}}",
-    "average": "average"
+    "average": "average",
+    "zoomReset": "Back to {{period}}",
+    "zoomed": "Zoom",
+    "dragToZoom": "Drag to zoom"
   },
   "commands": {
     "actionHint": "Server action",
-- 
2.54.0