second pass. low

site/src/components/ActivityCharts.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import * as Plot from '@observablehq/plot';
-  import { onMount } from 'svelte';
+  import { onMount, onDestroy } from 'svelte';
   import type { Timeseries, AthleteZones } from '../lib/types';
 
   export let timeseries: Timeseries;
@@ -82,8 +82,15 @@
   // Range handles — reset whenever the metric or chart type changes
   let trimMin = 0;
   let trimMax = 100;
-  $: if (dataMin !== undefined) resetTrim(dataMin, dataMax);
-  function resetTrim(lo: number, hi: number) { trimMin = lo; trimMax = hi; }
+  let lastResetTab: Tab | null = null;
+  $: {
+    // Reset trim on tab change OR when data range changes
+    if (activeTab !== lastResetTab || trimMin < dataMin || trimMax > dataMax) {
+      trimMin = dataMin;
+      trimMax = dataMax;
+      lastResetTab = activeTab;
+    }
+  }
 
   $: step = (dataMax - dataMin) / 200 || 1;
 
@@ -116,6 +123,7 @@
 
   // ── Rendering ────────────────────────────────────────────────────────────
   onMount(() => { renderChart(); });
+  onDestroy(() => { chart?.remove(); chart = null; });
 
   $: if (chartEl) {
     activeTab; xMode; chartType; histData; histThresholds; alignZones;