fix(player): decide transport in Rust for webview media (DR-097)

Video on Android/Linux renders in a webview <video> element, and the
frontend facade short-circuited play/pause/toggle straight into the
adapter whenever one was registered. Html5PlayerAdapter.toggle() then
decided play-vs-pause by reading el.paused off the DOM, so the Rust
controller never saw the intent and could not serialise competing ones.

el.paused flips transiently while an element buffers or settles a seek.
Two intents ~150ms apart therefore read *different* values and performed
*opposing* actions — one playing, one pausing — which self-sustained a
play/pause loop that needed no further input. On device this showed up
as a fully healthy element (readyState=4, networkState=1, not seeking,
not buffering, not ended) pausing itself roughly once a second, so
unpausing or skipping ahead bounced straight back to paused.

The root cause was that Rust held NO state for webview-rendered media:
report_html5_state only re-emitted its argument, despite the comment
above it claiming the controller was the single source of truth. It had
nothing to decide a toggle from.

Now report_html5_state tracks the reported state, and play/pause/toggle
consult it and drive the element by emitting a ControlCommand — the same
"backend decides, adapter executes the primitive" split player_seek_video
already uses. A stopped/idle report clears the tracking so MPV/ExoPlayer
regain authority for music playback.

Tests cover the loop signature directly (repeated toggles must alternate,
never repeat or oppose) plus a guard that one intent yields exactly one
ControlCommand — which matters on Windows, where the backend is itself
webview-based and could otherwise be driven twice.

src/lib/player/transport.authority.test.ts

@@ -0,0 +1,113 @@
+/**
+ * Transport authority: play/pause/toggle are DECIDED in Rust, never in the webview.
+ *
+ * TRACES: UR-005 | DR-097 | UT-089
+ *
+ * The frontend used to short-circuit transport controls whenever a video adapter
+ * was registered: `toggle()` read `el.paused` off the DOM and flipped the element
+ * directly, so the Rust `PlayerController` never saw the intent and could not
+ * serialise competing ones. Because `el.paused` flips transiently while an HTML5
+ * element buffers or settles a seek, two intents arriving ~150ms apart could read
+ * *different* values and perform *opposing* actions — one playing, one pausing —
+ * which is the self-sustaining play/pause loop observed on Android.
+ *
+ * The rule these tests pin: a transport intent always reaches the backend. Rust
+ * decides play-vs-pause from controller state and drives the webview element back
+ * through a ControlCommand event (the same "backend decides, adapter executes"
+ * split `player_seek_video` already uses).
+ */
+
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+const mockCommands = {
+  playerPlay: vi.fn(async () => ({})),
+  playerPause: vi.fn(async () => ({})),
+  playerToggle: vi.fn(async () => ({})),
+  playerStop: vi.fn(async () => ({})),
+};
+
+vi.mock("$lib/api/bindings", () => ({
+  commands: mockCommands,
+  // Stores pulled in transitively subscribe to typed events at module load.
+  events: {
+    playerStatusEvent: { listen: vi.fn(async () => () => {}) },
+    downloadEvent: { listen: vi.fn(async () => () => {}) },
+    searchEvent: { listen: vi.fn(async () => () => {}) },
+  },
+}));
+
+vi.mock("$lib/stores/auth", () => ({
+  auth: {
+    subscribe: (fn: (v: unknown) => void) => {
+      fn({ isAuthenticated: true });
+      return () => {};
+    },
+    getRepository: () => ({ getHandle: () => "handle-1" }),
+  },
+}));
+
+/** A video adapter that records whether the facade reached into it directly. */
+function makeAdapter() {
+  return {
+    kind: "html5" as const,
+    play: vi.fn(async () => {}),
+    pause: vi.fn(async () => {}),
+    toggle: vi.fn(async () => true),
+    seekElement: vi.fn(async () => {}),
+    reloadSource: vi.fn(async () => {}),
+    attach: vi.fn(),
+    dispose: vi.fn(async () => {}),
+    setVolume: vi.fn(),
+    setMuted: vi.fn(),
+    selectSubtitle: vi.fn(async () => {}),
+    getPosition: vi.fn(() => 0),
+    load: vi.fn(async () => {}),
+  };
+}
+
+describe("transport authority lives in Rust", () => {
+  let playerController: any;
+  let adapter: ReturnType<typeof makeAdapter>;
+
+  beforeEach(async () => {
+    vi.clearAllMocks();
+    vi.resetModules();
+    ({ playerController } = await import("./index"));
+    adapter = makeAdapter();
+    playerController.setActiveAdapter(adapter);
+  });
+
+  it("routes toggle to the backend even when a video adapter is active", async () => {
+    await playerController.toggle();
+
+    expect(mockCommands.playerToggle).toHaveBeenCalledTimes(1);
+    // The webview must NOT decide play-vs-pause from the DOM.
+    expect(adapter.toggle).not.toHaveBeenCalled();
+  });
+
+  it("routes play to the backend even when a video adapter is active", async () => {
+    await playerController.play();
+
+    expect(mockCommands.playerPlay).toHaveBeenCalledTimes(1);
+    expect(adapter.play).not.toHaveBeenCalled();
+  });
+
+  it("routes pause to the backend even when a video adapter is active", async () => {
+    await playerController.pause();
+
+    expect(mockCommands.playerPause).toHaveBeenCalledTimes(1);
+    expect(adapter.pause).not.toHaveBeenCalled();
+  });
+
+  it("still routes transport to the backend with no adapter (audio path unchanged)", async () => {
+    playerController.clearActiveAdapter();
+
+    await playerController.toggle();
+    await playerController.play();
+    await playerController.pause();
+
+    expect(mockCommands.playerToggle).toHaveBeenCalledTimes(1);
+    expect(mockCommands.playerPlay).toHaveBeenCalledTimes(1);
+    expect(mockCommands.playerPause).toHaveBeenCalledTimes(1);
+  });
+});