Keep wheel zoom inside the chart

e2e/planner.spec.ts

@@ -7,7 +7,13 @@ test.beforeEach(async ({ page }) => {
 
 test("zooms and toggles TaskNotes completion", async ({ page }) => {
   await expect(page.locator(".zoom-control output")).toHaveText("Weeks");
-  await page.getByRole("button", { name: "Zoom in" }).click();
+  const timeline = page.locator(".gantt-scroll");
+  const bounds = await timeline.boundingBox();
+  if (!bounds) throw new Error("Timeline bounds are unavailable.");
+  await page.mouse.move(bounds.x + bounds.width * 0.7, bounds.y + 180);
+  await page.keyboard.down("Control");
+  await page.mouse.wheel(0, -100);
+  await page.keyboard.up("Control");
   await expect(page.locator(".zoom-control output")).toHaveText("Work weeks");
 
   await page

src/components/gantt-chart.test.tsx

@@ -31,6 +31,85 @@ beforeEach(() => {
 });
 
 describe("GanttChart interactions", () => {
+  it("uses Ctrl+wheel for chart zoom without allowing Chrome page zoom", () => {
+    const task = makeTask({
+      id: "zoomable",
+      title: "Zoomable task",
+      scheduled: "2026-08-17",
+      due: "2026-08-18",
+    });
+    const onZoom = vi.fn();
+    const addEventListener = vi.spyOn(
+      HTMLElement.prototype,
+      "addEventListener",
+    );
+    render(
+      <GanttChart
+        allTasks={[task]}
+        selectedId={null}
+        tasks={[task]}
+        todayRequest={0}
+        zoom={3}
+        onDependenciesChange={vi.fn().mockResolvedValue(undefined)}
+        onCompletionChange={vi.fn().mockResolvedValue(undefined)}
+        onScheduleChange={vi.fn().mockResolvedValue(undefined)}
+        onSelect={() => undefined}
+        onZoom={onZoom}
+      />,
+    );
+
+    expect(addEventListener).toHaveBeenCalledWith(
+      "wheel",
+      expect.any(Function),
+      {
+        passive: false,
+      },
+    );
+
+    const surface = document.querySelector<HTMLElement>(".gantt-scroll")!;
+    const event = new WheelEvent("wheel", {
+      bubbles: true,
+      cancelable: true,
+      clientX: 600,
+      ctrlKey: true,
+      deltaY: -100,
+    });
+    surface.dispatchEvent(event);
+
+    expect(event.defaultPrevented).toBe(true);
+    expect(onZoom).toHaveBeenCalledWith(1);
+  });
+
+  it("leaves ordinary chart scrolling to the browser", () => {
+    const task = makeTask({ id: "scrollable", title: "Scrollable task" });
+    const onZoom = vi.fn();
+    render(
+      <GanttChart
+        allTasks={[task]}
+        selectedId={null}
+        tasks={[task]}
+        todayRequest={0}
+        zoom={3}
+        onDependenciesChange={vi.fn().mockResolvedValue(undefined)}
+        onCompletionChange={vi.fn().mockResolvedValue(undefined)}
+        onScheduleChange={vi.fn().mockResolvedValue(undefined)}
+        onSelect={() => undefined}
+        onZoom={onZoom}
+      />,
+    );
+
+    const surface = document.querySelector<HTMLElement>(".gantt-scroll")!;
+    const event = new WheelEvent("wheel", {
+      bubbles: true,
+      cancelable: true,
+      deltaY: 100,
+    });
+    surface.dispatchEvent(event);
+
+    expect(event.defaultPrevented).toBe(false);
+    expect(onZoom).not.toHaveBeenCalled();
+  });
+
   it("places an unscheduled task on the timeline by dragging", async () => {
     const task = makeTask({ id: "unscheduled", title: "Unscheduled" });
     const onScheduleChange = vi.fn().mockResolvedValue(undefined);

src/components/gantt-chart.tsx

@@ -1,12 +1,18 @@
 import { Check, GitBranch, Minus } from "lucide-react";
-import { useEffect, useLayoutEffect, useMemo, useRef, useState } from "react";
+import {
+  useCallback,
+  useEffect,
+  useLayoutEffect,
+  useMemo,
+  useRef,
+  useState,
+} from "react";
 
 import type {
   CSSProperties,
   KeyboardEvent as ReactKeyboardEvent,
   MutableRefObject,
   PointerEvent as ReactPointerEvent,
-  WheelEvent as ReactWheelEvent,
 } from "react";
 
 import {
@@ -525,25 +531,33 @@ export function GanttChart({
     };
   }
 
-  function handleWheel(event: ReactWheelEvent<HTMLDivElement>) {
-    if (!event.ctrlKey && !event.metaKey) return;
-    event.preventDefault();
+  const handleWheel = useCallback(
+    (event: WheelEvent) => {
+      if (!event.ctrlKey && !event.metaKey) return;
+      event.preventDefault();
+      const surface = scroller.current;
+      if (!surface || event.deltaY === 0) return;
+      const taskColumn = taskColumnWidth(surface);
+      const bounds = surface.getBoundingClientRect();
+      const viewportX = Math.max(taskColumn, event.clientX - bounds.left);
+      const timelineX = surface.scrollLeft + viewportX - taskColumn;
+      pendingZoomAnchor.current = {
+        minute:
+          planningMinute(scale.start)! +
+          (timelineX / scale.cellWidth) * DAY_MINUTES,
+        viewportX,
+      };
+      onZoom(event.deltaY < 0 ? 1 : -1);
+    },
+    [onZoom, scale.cellWidth, scale.start],
+  );
+
+  useEffect(() => {
     const surface = scroller.current;
-    if (!surface || event.deltaY === 0) return;
-    const bounds = surface.getBoundingClientRect();
-    const viewportX = Math.max(
-      taskColumnWidth(surface),
-      event.clientX - bounds.left,
-    );
-    const timelineX = surface.scrollLeft + viewportX - taskColumnWidth(surface);
-    pendingZoomAnchor.current = {
-      minute:
-        planningMinute(scale.start)! +
-        (timelineX / scale.cellWidth) * DAY_MINUTES,
-      viewportX,
-    };
-    onZoom(event.deltaY < 0 ? 1 : -1);
-  }
+    if (!surface) return;
+    surface.addEventListener("wheel", handleWheel, { passive: false });
+    return () => surface.removeEventListener("wheel", handleWheel);
+  }, [handleWheel, rows.length]);
 
   if (!rows.length)
     return (
@@ -558,7 +572,7 @@ export function GanttChart({
       className={`gantt-frame${linkDrag ? " is-linking" : ""}`}
       aria-label="Task timeline"
     >
-      <div className="gantt-scroll" ref={scroller} onWheel={handleWheel}>
+      <div className="gantt-scroll" ref={scroller}>
         <div
           className="gantt-canvas"
           style={{ width: TASK_COLUMN + timelineWidth }}