fix(story): harden notebook interaction and fallback

app/components/story/notebookTimeline.test.ts

@@ -64,8 +64,8 @@ describe("getNotebookFrame", () => {
   });
 
   it("emits a deterministic cursor click pulse for each tab", () => {
-    const first = getNotebookFrame(0.447, 4);
-    const later = getNotebookFrame(0.53, 4);
+    const first = getNotebookFrame(0.475, 4);
+    const later = getNotebookFrame(0.56, 4);
 
     expect(first.cursorClicking).toBe(true);
     expect(later.cursorClicking).toBe(true);
@@ -75,6 +75,17 @@ describe("getNotebookFrame", () => {
     expect(first.cursorY).toBeLessThanOrEqual(1);
   });
 
+  it("moves the cursor between tab targets instead of teleporting", () => {
+    const previous = getNotebookFrame(0.525, 4);
+    const moving = getNotebookFrame(0.532, 4);
+    const target = getNotebookFrame(0.56, 4);
+
+    expect(moving.cursorX).toBeGreaterThan(previous.cursorX);
+    expect(moving.cursorX).toBeLessThan(target.cursorX);
+    expect(moving.cursorY).toBeLessThan(previous.cursorY);
+    expect(moving.cursorY).toBeGreaterThan(target.cursorY);
+  });
+
   it("is deterministic when rewound to the same progress", () => {
     expect(getNotebookFrame(0.61, 4)).toEqual(getNotebookFrame(0.61, 4));
   });