fix(plex): Restart only where an episode has a resume point; the Surprise draw is re-read, not redrawn

Show cards carry resumable (ShowState, from the same rollup) so a part-watched
show whose next episode is untouched offers Play, not a Continue and a Restart
that do the same thing; plexStarted is the one rule for cards and menus. The
Surprise rail's key sits under the discover root: whatever refreshes the rails
re-reads the draw (keep=) with its watch state now, kept past the 5-minute gc,
and only the reshuffle deals. Closing the player refreshes the Discover rails.
A show card's play acts on the last click only, and only where it was made.

frontend/src/components/usePlayShow.dom.test.tsx

@@ -30,12 +30,23 @@ function mount() {
   const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
   const play = vi.fn();
   const openShow = vi.fn();
-  const { result } = renderHook(() => usePlayShow(play, openShow), {
-    wrapper: ({ children }: { children: ReactNode }) => (
-      <QueryClientProvider client={qc}>{children}</QueryClientProvider>
-    ),
-  });
-  return { qc, play, openShow, playShow: result.current };
+  const { result, rerender, unmount } = renderHook(
+    ({ here }: { here: unknown }) => usePlayShow(play, openShow, here),
+    {
+      initialProps: { here: "grid" as unknown },
+      wrapper: ({ children }: { children: ReactNode }) => (
+        <QueryClientProvider client={qc}>{children}</QueryClientProvider>
+      ),
+    },
+  );
+  return { qc, play, openShow, playShow: result.current, rerender, unmount };
+}
+
+/** Answers the test hands out one by one, in the order it chooses. */
+function answers() {
+  const pending: ((v: { next: PlexCard | null }) => void)[] = [];
+  vi.spyOn(api, "plexShowNext").mockImplementation(() => new Promise((r) => void pending.push(r)));
+  return pending;
 }
 
 describe("usePlayShow", () => {
@@ -65,6 +76,32 @@ describe("usePlayShow", () => {
     expect(play).not.toHaveBeenCalled();
   });
 
+  it("acts on the last click only: an earlier, slower answer is dropped", async () => {
+    const pending = answers();
+    const { play, playShow } = mount();
+    const first = playShow({ ...show, id: "a" }, false);
+    const second = playShow({ ...show, id: "b" }, false);
+    await act(async () => pending[1]!({ next: ep("b1") }));
+    await act(async () => pending[0]!({ next: ep("a1") }));
+    await act(() => Promise.all([first, second]));
+    expect(play.mock.calls).toEqual([["b1", false]]);
+  });
+
+  it("drops an answer that lands after the viewer has moved on, or left", async () => {
+    const pending = answers();
+    const { play, openShow, playShow, rerender, unmount } = mount();
+    const moved = playShow(show, false);
+    rerender({ here: "info" });
+    await act(async () => pending[0]!({ next: ep("e1") }));
+    await act(() => moved);
+    expect(play).not.toHaveBeenCalled();
+    const left = playShow(show, false);
+    unmount();
+    await act(async () => pending[1]!({ next: null }));
+    await act(() => left);
+    expect(openShow).not.toHaveBeenCalled();
+  });
+
   it("says so when the question fails, and opens nothing", async () => {
     vi.spyOn(api, "plexShowNext").mockRejectedValue(new Error("down"));
     const { play, openShow, playShow } = mount();