fix(player): re-entering a video no longer opens the audio player (DR-100)

Leaving a video and returning to it rendered the movie/episode in
AudioPlayer. Closing a webview-rendered video deliberately emits no
"stopped" state (that would break the autoplay handoff), and the
direct-play path does not stop the backend on unmount, so the Rust
controller still reported that item as its loaded media. Re-entering the
route therefore took the "already playing, just show the UI" shortcut,
which returns before a stream URL is fetched, and the render fell
through to the audio surface. Mostly visible on Android, where video
direct-plays; Linux transcodes and stops the backend on unmount.

Both decisions move into playerSurface.ts as pure functions:
shouldReuseActivePlayback excludes video, so video always takes the full
load path and gets its stream URL and resume position;
resolvePlayerSurface maps video-without-a-stream-URL to "pending"
(spinner) rather than falling through to audio.

src/lib/components/player/playerSurface.test.ts

@@ -0,0 +1,107 @@
+/**
+ * Regression tests for the `/player/[id]` surface decision.
+ *
+ * The bug these pin down: a video that was left and re-entered rendered in the
+ * AUDIO player. Exiting a webview-rendered video does not stop the Rust
+ * controller (`onReportStop` deliberately emits no `stopped` state, so the
+ * autoplay handoff survives), so the backend still reports that episode/movie as
+ * the loaded media. Re-entering the route therefore took the "already playing,
+ * just show the UI" shortcut, which returns *before* a stream URL is fetched —
+ * and the render then fell through to `<AudioPlayer>` because it treated
+ * "video without a stream URL" as audio.
+ *
+ * TRACES: UR-005 | DR-100 | UT-092, UT-093
+ */
+
+import { describe, it, expect } from "vitest";
+import { shouldReuseActivePlayback, resolvePlayerSurface } from "./playerSurface";
+
+describe("shouldReuseActivePlayback", () => {
+  it("reuses playback when the same audio track is already loaded", () => {
+    expect(
+      shouldReuseActivePlayback({
+        requestedId: "track-1",
+        activeMediaId: "track-1",
+        isVideo: false,
+        forceRestart: false,
+      })
+    ).toBe(true);
+  });
+
+  it("does NOT reuse playback for video, even when the backend reports it loaded", () => {
+    // Video needs a full load: the shortcut skips fetching the stream URL, and
+    // <VideoPlayer> cannot render without one.
+    expect(
+      shouldReuseActivePlayback({
+        requestedId: "episode-1",
+        activeMediaId: "episode-1",
+        isVideo: true,
+        forceRestart: false,
+      })
+    ).toBe(false);
+  });
+
+  it("does not reuse playback for a different item", () => {
+    expect(
+      shouldReuseActivePlayback({
+        requestedId: "track-2",
+        activeMediaId: "track-1",
+        isVideo: false,
+        forceRestart: false,
+      })
+    ).toBe(false);
+  });
+
+  it("does not reuse playback when nothing is loaded", () => {
+    expect(
+      shouldReuseActivePlayback({
+        requestedId: "track-1",
+        activeMediaId: null,
+        isVideo: false,
+        forceRestart: false,
+      })
+    ).toBe(false);
+  });
+
+  it("does not reuse playback when an explicit start position is requested", () => {
+    expect(
+      shouldReuseActivePlayback({
+        requestedId: "track-1",
+        activeMediaId: "track-1",
+        isVideo: false,
+        startPosition: 42,
+        forceRestart: false,
+      })
+    ).toBe(false);
+  });
+
+  it("does not reuse playback when restarting (next-episode advance)", () => {
+    expect(
+      shouldReuseActivePlayback({
+        requestedId: "episode-2",
+        activeMediaId: "episode-2",
+        isVideo: true,
+        forceRestart: true,
+      })
+    ).toBe(false);
+  });
+});
+
+describe("resolvePlayerSurface", () => {
+  it("renders the video surface for video with a stream URL", () => {
+    expect(resolvePlayerSurface({ isVideo: true, streamUrl: "http://s/master.m3u8" })).toBe(
+      "video"
+    );
+  });
+
+  it("renders the audio surface for audio content", () => {
+    expect(resolvePlayerSurface({ isVideo: false, streamUrl: null })).toBe("audio");
+  });
+
+  it("never renders video content in the audio surface when the stream URL is missing", () => {
+    // A video whose stream URL has not resolved yet is pending, not audio —
+    // otherwise the movie/episode shows up in the audio player.
+    expect(resolvePlayerSurface({ isVideo: true, streamUrl: null })).toBe("pending");
+    expect(resolvePlayerSurface({ isVideo: true, streamUrl: "" })).toBe("pending");
+  });
+});