fix(web): thread jump hints wait for their delay on every hold (#25636)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: juliusmarminge

apps/web/src/components/Sidebar.logic.browser.test.tsx

@@ -1,7 +1,7 @@
 import { describe, expect, it, vi } from "vite-plus/test";
 
-import { render } from "../../test/render";
-import { useSnoozeWakeClock } from "./Sidebar.logic";
+import { act, fakeTimers, render } from "../../test/render";
+import { useSnoozeWakeClock, useThreadJumpHintsVisible } from "./Sidebar.logic";
 
 const MOUNTED_AT_MS = Date.parse("2026-10-24T08:00:00.000Z");
 
@@ -31,3 +31,29 @@ describe("useSnoozeWakeClock", () => {
     await expect.element(screen.getByRole("status")).toHaveTextContent(String(lastWakeMs));
   });
 });
+
+function JumpHints(props: { readonly held: boolean }) {
+  return <output>{useThreadJumpHintsVisible(props.held) ? "shown" : "hidden"}</output>;
+}
+
+describe("useThreadJumpHintsVisible", () => {
+  it("waits for the delay again on a second hold", async () => {
+    // The first render reads the clock.
+    using _timers = fakeTimers({ now: 0 });
+    await using screen = await render(<JumpHints held />, {
+      // A bare hook host; nothing here links or navigates.
+      router: false,
+    });
+    await act(() => vi.advanceTimersByTime(1_000));
+    await expect.element(screen.getByRole("status")).toHaveTextContent("shown");
+
+    await screen.rerender(<JumpHints held={false} />);
+    await expect.element(screen.getByRole("status")).toHaveTextContent("hidden");
+    await act(() => vi.advanceTimersByTime(1_000));
+
+    await screen.rerender(<JumpHints held />);
+    await expect.element(screen.getByRole("status")).toHaveTextContent("hidden");
+    await act(() => vi.advanceTimersByTime(1_000));
+    await expect.element(screen.getByRole("status")).toHaveTextContent("shown");
+  });
+});

apps/web/src/components/Sidebar.logic.ts

@@ -670,10 +670,13 @@ type ThreadStatusInput = Pick<
  */
 export function useThreadJumpHintsVisible(shouldShow: boolean): boolean {
   const [showAt, setShowAt] = React.useState<number | null>(null);
-  let nextShowAt = shouldShow ? showAt : null;
-  if (shouldShow && showAt === null) nextShowAt = deadlineAfter(THREAD_JUMP_HINT_SHOW_DELAY_MS);
-  if (nextShowAt !== showAt) setShowAt(nextShowAt);
-  return useDeadlinePassed(nextShowAt);
+  // The clock is read inside the updater: the compiler caches a bare clock read
+  // in render once per instance, so a second hold would reuse the first deadline.
+  // React discards this render and re-runs with the update.
+  if (shouldShow !== (showAt !== null)) {
+    setShowAt(shouldShow ? () => deadlineAfter(THREAD_JUMP_HINT_SHOW_DELAY_MS) : null);
+  }
+  return useDeadlinePassed(showAt);
 }
 
 export function resolveThreadLastVisitedAt(