Revert homepage

frontend/src/hooks/useMapData.ts

@@ -448,16 +448,26 @@ export function useMapData({
   ]);
 
   // Use drag data only when it matches the current view feature and request key.
+  // The first render of a new drag must not reuse the previous drag's preview range.
+  const dragJustStarted =
+    Boolean(activeFeature) &&
+    (previousDragStateRef.current.activeFeature !== activeFeature ||
+      previousDragStateRef.current.filterStateKey !== filterStateKey);
   const hasMatchingDragData =
+    !dragJustStarted &&
     Boolean(activeFeature && viewFeature && activeDragRequest) &&
     dragFeatureRef.current === viewFeature &&
     dragDataKey === activeDragRequest?.requestKey;
+  const hasCurrentRangeData = activeFeature
+    ? hasMatchingDragData
+    : loadedDataKey === dataRequestKey;
   const data = (hasMatchingDragData ? dragHexData : null) ?? rawData;
   const effectivePostcodeData = (hasMatchingDragData ? dragPostcodeData : null) ?? postcodeData;
 
   // Compute p5/p95 from the data currently being drawn. During slider drags
   // this uses the drag-preview data so the colour scale resets to that preview.
   const dataRange = useMemo((): [number, number] | null => {
+    if (!hasCurrentRangeData) return null;
     if (!dataViewFeature) return null;
 
     const isTravelTime = dataViewFeature.startsWith('tt_');
@@ -499,7 +509,15 @@ export function useMapData({
       percentile(vals, COLOR_RANGE_LOW_PERCENTILE),
       percentile(vals, COLOR_RANGE_HIGH_PERCENTILE),
     ];
-  }, [dataViewFeature, data, effectivePostcodeData, usePostcodeView, features, bounds]);
+  }, [
+    bounds,
+    data,
+    dataViewFeature,
+    effectivePostcodeData,
+    features,
+    hasCurrentRangeData,
+    usePostcodeView,
+  ]);
 
   // Live color range for the legend and hex coloring.
   const liveColorRange = useMemo((): [number, number] | null => {
@@ -516,19 +534,11 @@ export function useMapData({
       return [0, meta.values.length - 1];
     }
     if (dataRange) return dataRange;
-    if (activeFeature && !hasMatchingDragData) return null;
+    if (activeFeature) return null;
     if (loadedDataKey !== dataRequestKey) return null;
     if (meta.min != null && meta.max != null) return [meta.min, meta.max];
     return null;
-  }, [
-    activeFeature,
-    dataRequestKey,
-    dataRange,
-    dataViewFeature,
-    features,
-    hasMatchingDragData,
-    loadedDataKey,
-  ]);
+  }, [activeFeature, dataRequestKey, dataRange, dataViewFeature, features, loadedDataKey]);
 
   const isEyePreviewingPinnedFeature =
     !activeFeature && dataViewFeature != null && dataViewFeature === pinnedDataViewFeature;