fix(web): limit minimap wheel scrolling to the hit strip

apps/web/src/components/chat/MessagesTimeline.logic.test.ts

@@ -7,6 +7,7 @@ import {
   resolveAssistantMessageCopyState,
   resolveTimelineMinimapWheelIndex,
   shouldPreserveAssistantLineBreaks,
+  timelineMinimapWheelTargetsHitStrip,
 } from "./MessagesTimeline.logic";
 
 describe("resolveTimelineMinimapWheelIndex", () => {
@@ -34,6 +35,28 @@ describe("resolveTimelineMinimapWheelIndex", () => {
   });
 });
 
+describe("timelineMinimapWheelTargetsHitStrip", () => {
+  it("accepts wheel events over the minimap bars", () => {
+    expect(
+      timelineMinimapWheelTargetsHitStrip({
+        pointerX: 24,
+        hitStripLeft: 12,
+        hitStripWidth: 40,
+      }),
+    ).toBe(true);
+  });
+
+  it("rejects wheel events over the expanded preview", () => {
+    expect(
+      timelineMinimapWheelTargetsHitStrip({
+        pointerX: 100,
+        hitStripLeft: 12,
+        hitStripWidth: 40,
+      }),
+    ).toBe(false);
+  });
+});
+
 describe("shouldPreserveAssistantLineBreaks", () => {
   it("preserves Claude insight formatting without changing regular markdown", () => {
     expect(

apps/web/src/components/chat/MessagesTimeline.logic.ts

@@ -104,6 +104,26 @@ export function resolveTimelineMinimapWheelIndex(input: {
   return Math.max(0, Math.min(input.itemCount - 1, currentIndex + direction));
 }
 
+export function timelineMinimapWheelTargetsHitStrip(input: {
+  readonly pointerX: number;
+  readonly hitStripLeft: number;
+  readonly hitStripWidth: number;
+}): boolean {
+  if (
+    !Number.isFinite(input.pointerX) ||
+    !Number.isFinite(input.hitStripLeft) ||
+    !Number.isFinite(input.hitStripWidth) ||
+    input.hitStripWidth <= 0
+  ) {
+    return false;
+  }
+
+  return (
+    input.pointerX >= input.hitStripLeft &&
+    input.pointerX <= input.hitStripLeft + input.hitStripWidth
+  );
+}
+
 export function resolveTimelineMinimapHasPersistentGutter(viewportWidth: number): boolean {
   if (!Number.isFinite(viewportWidth) || viewportWidth <= 0) {
     return false;

apps/web/src/components/chat/MessagesTimeline.tsx

@@ -86,6 +86,7 @@ import {
   resolveTimelineMinimapTopPercent,
   resolveTimelineMinimapWheelIndex,
   shouldPreserveAssistantLineBreaks,
+  timelineMinimapWheelTargetsHitStrip,
   type StableMessagesTimelineRowsState,
   type MessagesTimelineRow,
   TIMELINE_MINIMAP_MIN_ITEMS,
@@ -787,6 +788,16 @@ function TimelineMinimap({
       }
 
       const rect = button.getBoundingClientRect();
+      if (
+        !timelineMinimapWheelTargetsHitStrip({
+          pointerX: event.clientX,
+          hitStripLeft: rect.left,
+          hitStripWidth,
+        })
+      ) {
+        return;
+      }
+
       const pointerIndex = resolveTimelineMinimapIndexFromPointer({
         itemCount: items.length,
         railTop: rect.top,
@@ -815,7 +826,7 @@ function TimelineMinimap({
       wheelIndexRef.current = nextIndex;
       onSelect(nextItem);
     },
-    [items, onSelect],
+    [hitStripWidth, items, onSelect],
   );
 
   useEffect(() => {