fix(plex): an episode Plex has no number for is named by its title alone

The OS media title printed the missing number as "Enull", the player and info headers as a bare
"E". One helper for the three lines.

frontend/src/components/PlexInfo.tsx

@@ -10,6 +10,7 @@ import { DetailCustomizeMenu, Filterable, PrefToggle } from "./plexDetailUi";
 import { DetailAside, DetailAsideToggles, DetailKeywords } from "./plexDetailAside";
 import {
   DETAIL_POSTER,
+  episodeLine,
   tmdbBackdropUrl,
   useCrossfadeBackdrop,
   useDetailAside,
@@ -315,7 +316,7 @@ export default function PlexInfo({
               )}
               {detail.kind === "episode" && (
                 <p className={`text-sm ${overlay ? "text-white/70" : "text-muted"}`}>
-                  S{detail.season_number}·E{detail.episode_number} — {detail.title}
+                  {episodeLine(detail)}
                 </p>
               )}
             </div>

frontend/src/components/PlexPlayer.tsx

@@ -52,6 +52,7 @@ import { Ctrl, PanelHead } from "./plexPlayerControls";
 import { PlexPlayerSettings } from "./PlexPlayerSettings";
 import { PlexStatsOverlay } from "./PlexStatsOverlay";
 import { createFragMeter } from "../lib/plexStats";
+import { episodeLine } from "../lib/plexDetail";
 import { HlsEngine } from "../lib/hlsEngine";
 import { createHlsPort } from "../lib/hlsPort";
 import { enabled, log } from "../lib/log";
@@ -586,10 +587,7 @@ export default function PlexPlayer({ itemId, onClose, queue, fromStart = false }
   useMediaSession(
     videoEl,
     detail && {
-      title:
-        detail.kind === "episode" && detail.season_number != null
-          ? `S${detail.season_number}·E${detail.episode_number} — ${detail.title}`
-          : detail.title,
+      title: detail.kind === "episode" ? episodeLine(detail) : detail.title,
       artist:
         detail.kind === "episode" ? detail.show_title : detail.year ? String(detail.year) : null,
       artwork: api.plexImageUrl(id),
@@ -1258,9 +1256,7 @@ export default function PlexPlayer({ itemId, onClose, queue, fromStart = false }
               {detail?.kind === "episode" && detail.show_title ? detail.show_title : detail?.title}
             </div>
             {detail?.kind === "episode" && (
-              <div className="text-xs text-white/70 truncate">
-                S{detail.season_number}·E{detail.episode_number} — {detail.title}
-              </div>
+              <div className="text-xs text-white/70 truncate">{episodeLine(detail)}</div>
             )}
           </div>
           {/* Live wall clock — handy on a lean-back / HTPC screen (toggle + style in the Clock tab). */}

frontend/src/lib/plexDetail.episodeLine.test.ts

@@ -0,0 +1,20 @@
+// @vitest-environment jsdom
+import { describe, expect, it } from "vitest";
+import { episodeLine } from "./plexDetail";
+
+describe("episodeLine", () => {
+  it("names the episode by its season and number", () => {
+    expect(episodeLine({ season_number: 2, episode_number: 7, title: "Pilot" })).toBe(
+      "S2·E7 — Pilot",
+    );
+  });
+
+  it("is the title alone for an episode Plex has no number for", () => {
+    expect(episodeLine({ season_number: 1, episode_number: null, title: "Special" })).toBe(
+      "Special",
+    );
+    expect(episodeLine({ season_number: null, episode_number: 3, title: "Special" })).toBe(
+      "Special",
+    );
+  });
+});

frontend/src/lib/plexDetail.ts

@@ -210,6 +210,17 @@ export function epLabel(ep?: PlexCard | null): string | undefined {
   return ep.title;
 }
 
+/** An episode's line under its show's name: "S1·E4 — Title" — or the title alone when Plex has no
+ *  number for it (a special): a template literal printed the missing one as "Enull", JSX as "E". */
+export function episodeLine(ep: {
+  season_number?: number | null;
+  episode_number?: number | null;
+  title: string;
+}): string {
+  if (ep.season_number == null || ep.episode_number == null) return ep.title;
+  return `S${ep.season_number}·E${ep.episode_number} — ${ep.title}`;
+}
+
 // Plex names seasons in the library's language ("Season 1", "Specials"), so a Hungarian reader got
 // English there. A generic name is rebuilt from the number in the reader's language; a season
 // with a name of its own ("Book One: Water") keeps it.