fix(player): a session superseded before it played is reclaimed, not "couldn't start"

Two session requests for one item in flight at once (a quick double seek; the
StrictMode replay of the start effect) let the server's last spawn be the older
request's. The newer request's answer then named a session already gone; its
playlist 404'd before a manifest parsed, and the player stopped with "Playback
couldn't start". The 404 reclaim now covers a session that never played too,
bounded by the same budget, and keeps the start's own autoplay.

frontend/src/components/PlexPlayer.hls.dom.test.tsx

@@ -248,12 +248,35 @@ describe("an HLS session the server no longer has", () => {
     }
   });
 
-  it("is a failure, not a restart, when the session never played", async () => {
-    // Otherwise a session that 404s from the start would restart itself in a loop.
+  it("is reclaimed at the asked position, and still starts, when it was lost before it played", async () => {
+    // Two session requests for one item in flight at once (a seek twice in quick succession; the
+    // dev StrictMode replay of the start effect): the server's LAST spawn wins, and it may be the
+    // older request's. The newer request's answer then names a session that is already gone, and
+    // its playlist 404s before a single manifest parsed — which ended playback with "couldn't
+    // start" (Arrow S03E14 on localdev, 2026-09-27). The video is still paused then, so the
+    // reclaim must keep the start's own "play once ready", not read it off the paused element.
+    const play = vi.spyOn(HTMLMediaElement.prototype, "play");
     const session = mount();
     await waitFor(() => expect(hlsInstances).toHaveLength(1));
-    act(() => hlsInstances[0]!.emit(Hls.Events.ERROR, lost404));
+    act(() =>
+      hlsInstances[0]!.emit(Hls.Events.ERROR, { ...lost404, details: "manifestLoadError" }),
+    );
+    await waitFor(() => expect(hlsInstances).toHaveLength(2));
+    expect(session).toHaveBeenCalledTimes(2);
+    expect(session.mock.calls[1]![1]).toBe(600);
+    act(() => hlsInstances[1]!.emit(Hls.Events.MANIFEST_PARSED));
+    expect(play).toHaveBeenCalled();
+    expect(screen.queryByText("plex.player.errGeneric")).toBeNull();
+  });
+
+  it("gives up and says so when a session that never played keeps 404ing", async () => {
+    // The reclaim budget is what bounds a server that 404s every session from the start.
+    const session = mount();
+    for (let i = 0; i < 3; i++) {
+      await waitFor(() => expect(hlsInstances).toHaveLength(i + 1));
+      act(() => hlsInstances[i]!.emit(Hls.Events.ERROR, lost404));
+    }
     await screen.findByText("plex.player.errGeneric");
-    expect(session).toHaveBeenCalledTimes(1);
+    expect(session).toHaveBeenCalledTimes(3);
   });
 });