Introduce PlayerAdapter contract; decision logic shared in Rust backend

Establish a decoupled player boundary so UI and backend interact with video
through one contract, with the HTML5 (Linux/interim-Android) and native
(ExoPlayer) providers as interchangeable primitive-executor adapters.

- PlayerAdapter interface + AdapterHost callback bag (adapters/types.ts): the
  adapter owns only decision-free element PRIMITIVES (seekElement, reloadSource,
  play/pause, setVolume, selectSubtitle); it never branches on strategy.
- Seek/audio-track DECISIONS stay in Rust (player_seek_video / _switch_audio_track
  return a strategy); the facade dispatches the chosen primitive to the active
  adapter. Both providers share the one decision path — logic lives once, in Rust.
- Facade holds the active adapter; a new ControlCommand PlayerStatusEvent lets
  backend control (lockscreen/remote/sleep) drive the webview <video> element.
- Html5PlayerAdapter resolves the LIVE element via the bridge (fixes play/pause
  silently no-opping when the element was re-bound).
- Do not emit a "stopped" player state on natural end-of-video: it flipped the
  player/mode to idle mid-handoff and suppressed next-episode auto-advance under
  a sleep timer. Jellyfin progress reporting is preserved; the backend's
  on_video_playback_ended owns the transition.
- VideoPlayer net -300 lines (strategy/HLS-reload logic relocated to the adapter).
- Adds 20 adapter unit tests; existing suites stay green (vitest 457, cargo 416).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/player/adapters/rustReportHost.ts

@@ -0,0 +1,93 @@
+/**
+ * An {@link AdapterHost} implementation that forwards a player adapter's outward
+ * lifecycle events into the Rust `PlayerController` via the `player_report_*`
+ * commands. The controller re-emits the same `PlayerStatusEvent`s the native
+ * backends emit, so the frontend `player` store is fed from ONE pipeline
+ * (playerEvents.ts) in both native and HTML5 modes — keeping Rust the single
+ * source of truth.
+ *
+ * This is the sole place that talks to the report commands; adapters depend only
+ * on the {@link AdapterHost} interface, never on `commands` directly, which keeps
+ * them unit-testable with a mock host.
+ *
+ * TRACES: UR-003, UR-005 | DR-001, DR-028
+ */
+
+import { commands } from "$lib/api/bindings";
+import type { AdapterHost } from "./types";
+
+const POSITION_REPORT_INTERVAL_MS = 250;
+
+/** Report options that let a caller bypass throttling for discrete events. */
+export interface ReportPositionOptions {
+  force?: boolean;
+}
+
+/**
+ * Low-level report helpers, exported so the legacy `$lib/player/html5Adapter`
+ * shim can keep its function-style API while there are still direct callers.
+ * Prefer {@link createRustReportHost} for new adapter code.
+ */
+let lastPositionReport = 0;
+
+export async function reportState(
+  state: "playing" | "paused" | "loading" | "stopped" | "idle",
+  mediaId: string | null
+): Promise<void> {
+  try {
+    await commands.playerReportState(state, mediaId);
+  } catch (err) {
+    console.warn("[rustReportHost] Failed to report state:", err);
+  }
+}
+
+export async function reportPosition(
+  position: number,
+  duration: number,
+  { force = false }: ReportPositionOptions = {}
+): Promise<void> {
+  const now = Date.now();
+  if (!force && now - lastPositionReport < POSITION_REPORT_INTERVAL_MS) {
+    return;
+  }
+  lastPositionReport = now;
+  try {
+    await commands.playerReportPosition(position, Number.isFinite(duration) ? duration : 0);
+  } catch (err) {
+    console.warn("[rustReportHost] Failed to report position:", err);
+  }
+}
+
+export async function reportMediaLoaded(duration: number): Promise<void> {
+  try {
+    await commands.playerReportMediaLoaded(Number.isFinite(duration) ? duration : 0);
+  } catch (err) {
+    console.warn("[rustReportHost] Failed to report media loaded:", err);
+  }
+}
+
+export function resetReporting(): void {
+  lastPositionReport = 0;
+}
+
+/**
+ * Build an {@link AdapterHost} bound to a specific media id that forwards adapter
+ * events to Rust. `onStreamUrlChanged`, `onBuffering`, and `onReady` are wired by
+ * the owning view (they affect the `<video src>` / spinner), so this host accepts
+ * optional view callbacks and defaults them to no-ops.
+ */
+export function createRustReportHost(
+  mediaId: string,
+  view: Partial<Pick<AdapterHost, "onStreamUrlChanged" | "onBuffering" | "onReady" | "onEnded" | "onError">> = {}
+): AdapterHost {
+  return {
+    onState: (state) => void reportState(state, mediaId),
+    onPosition: (position, duration) => void reportPosition(position, duration),
+    onMediaLoaded: (duration) => void reportMediaLoaded(duration),
+    onEnded: view.onEnded ?? (() => {}),
+    onError: view.onError ?? ((message) => console.warn("[rustReportHost] adapter error:", message)),
+    onStreamUrlChanged: view.onStreamUrlChanged ?? (() => {}),
+    onBuffering: view.onBuffering ?? (() => {}),
+    onReady: view.onReady ?? (() => {}),
+  };
+}