fix(ui,player): scroll restore, immersive fullscreen, watched toggle, handoff timeline, PiP

Batch of reported bugs and enhancements.

UI
- Pages no longer inherit the previous page's scroll position (DR-156, UR-072).
  The shell keeps its scrollers alive across navigation by design, so the
  element never remounts and its scrollTop survived the route change; SvelteKit
  restores window scroll, which this app never uses. ScrollMemory records the
  offset per route and per container: forward moves reset to the top, Back
  restores where the route was left.
- Season header stacks on narrow screens, and the title span gets min-w-0 so it
  actually truncates instead of overflowing under the action buttons.
- Favourites gets a labelled tile at the head of the library grid rather than
  only an unlabelled heart icon in the header.

Playback
- Full-screen video on Android hides the system bars (DR-157, UR-066).
  requestFullscreen() cannot touch the Activity window from inside a WebView, so
  the control did nothing visible while the bars stayed painted over the video.
  ImmersiveModeBridge hides them, restored on exit, Escape and teardown.
- Background-audio handoff stops leaking its relative timeline (DR-159).
  background_audio_base was a display-only correction applied in two places
  while progress reports to Jellyfin, the frontend and media3's own seeks all
  worked in the relative timeline treating it as absolute — each crossing losing
  exactly `base` seconds. The conversion now happens once, in the position tick,
  and inbound seeks resolve through seek_absolute, which re-opens the stream at
  the requested position because the handoff transcode cannot seek.
- Picture-in-picture works on the path that actually plays video (DR-160).
  canEnterPip demanded a native ExoPlayer surface, but that path is behind a
  flag defaulting to off, so PiP could never engage. It now accepts the WebView
  <video> too, keeping the WebView visible and routing play/pause to the element.
- Native video is now the default so PiP has a real surface (DR-161). The
  scrub-regression tests pinned the flag-off path implicitly; they now mock it
  off explicitly. The native scrub/seek path is not covered by the suite and
  needs device verification.

Watched state
- Watched toggle on the episode row, season header, series and movie hero, and
  the Episode Focus View (DR-158, UR-073). Both backend halves already existed
  with no caller. storage_set_watched covers a container's episodes so the
  toggle is honest offline, and QueuedOp::MarkUnplayed gives the sync queue the
  missing direction.

Release
- Fix the Android versionCode floor (set-version.sh). v0.5.2 shipped code 5002
  under an earlier minor*1000 scheme, but the current minor*100 formula yields
  1502 for that version and 1503 for 0.5.3 — so every 0.5.x release built from
  it was an un-installable downgrade for anyone already on v0.5.2. Widened to
  10000 + major*1000000 + minor*1000 + patch (0.5.3 -> 15003).
- Bump to 0.5.3.

src/lib/utils/immersive.ts

@@ -0,0 +1,68 @@
+/**
+ * Immersive (system-bar-free) full-screen video, Android only.
+ *
+ * TRACES: UR-066 | DR-157
+ *
+ * `requestFullscreen()` is the only fullscreen control the web layer has, and in
+ * an Android WebView it does not touch the Activity window — it expands the
+ * element inside a viewport that already spans the whole screen (MainActivity
+ * calls `enableEdgeToEdge()`, and SDK 36 makes that mandatory). So the status and
+ * navigation bars stayed painted over full-screen video, and "fullscreen"
+ * changed nothing visible.
+ *
+ * Hiding them needs `WindowInsetsControllerCompat` on the Activity, so it goes
+ * through the `AndroidImmersive` @JavascriptInterface installed by MainActivity.
+ * Elsewhere (desktop, the Linux WebKitGTK webview) the real `requestFullscreen()`
+ * already does the right thing and these calls are no-ops.
+ */
+
+interface AndroidImmersiveBridge {
+  enter(): void;
+  exit(): void;
+  isSupported(): boolean;
+}
+
+declare global {
+  interface Window {
+    AndroidImmersive?: AndroidImmersiveBridge;
+  }
+}
+
+function bridge(): AndroidImmersiveBridge | undefined {
+  if (typeof window === "undefined") return undefined;
+  return window.AndroidImmersive;
+}
+
+/** Whether native immersive mode exists on this platform. */
+export function isImmersiveSupported(): boolean {
+  try {
+    return bridge()?.isSupported() ?? false;
+  } catch (err) {
+    console.warn("[Immersive] isSupported check failed:", err);
+    return false;
+  }
+}
+
+/** Hide the system bars. No-op where unsupported. */
+export function enterImmersive(): void {
+  try {
+    bridge()?.enter();
+  } catch (err) {
+    console.error("[Immersive] Failed to hide the system bars:", err);
+  }
+}
+
+/**
+ * Restore the system bars. No-op where unsupported.
+ *
+ * Call this on leaving fullscreen *and* on player teardown — the bars belong to
+ * the Activity, not the player, so a player destroyed while immersive would
+ * leave every screen behind it without a status or navigation bar.
+ */
+export function exitImmersive(): void {
+  try {
+    bridge()?.exit();
+  } catch (err) {
+    console.error("[Immersive] Failed to restore the system bars:", err);
+  }
+}

src/lib/utils/pictureInPicture.ts

@@ -18,6 +18,7 @@ interface AndroidPictureInPictureBridge {
   isSupported(): boolean;
   canEnterPip(): boolean;
   setAutoEnterEnabled(enabled: boolean): void;
+  setHtml5VideoState(active: boolean, width: number, height: number, playing: boolean): void;
 }
 
 declare global {
@@ -84,3 +85,32 @@ export function setAutoEnterEnabled(enabled: boolean): void {
     console.warn("[PiP] Failed to set auto-enter:", err);
   }
 }
+
+/**
+ * Tell native that a WebView `<video>` is (or is no longer) the playback surface.
+ *
+ * This is what makes PiP work at all in the shipping configuration. The native
+ * side only ever knew about the ExoPlayer surface, and that path is behind
+ * `experimentalNativeVideo`, which defaults to off — so `canEnterPip` was always
+ * false and pressing the button did nothing. Reporting the element's state gives
+ * native a surface it can legitimately shrink into, plus the intrinsic size it
+ * needs for the PiP window's aspect ratio and the play state for its play/pause
+ * action.
+ *
+ * Pass `active: false` when the element goes away, or PiP would be offered over a
+ * video that is no longer there.
+ *
+ * TRACES: UR-041 | DR-160
+ */
+export function setHtml5VideoState(
+  active: boolean,
+  width: number,
+  height: number,
+  playing: boolean
+): void {
+  try {
+    bridge()?.setHtml5VideoState(active, Math.round(width), Math.round(height), playing);
+  } catch (err) {
+    console.warn("[PiP] Failed to report HTML5 video state:", err);
+  }
+}

src/lib/utils/scrollContainer.ts

@@ -0,0 +1,90 @@
+/**
+ * Wires a persistent scroll container to the per-route scroll memory.
+ *
+ * The decision logic is pure and lives in `scrollRestore.ts`; this is the thin
+ * DOM/SvelteKit half. Call it once at component init (SvelteKit's navigation
+ * hooks must be registered during initialisation, not from `onMount`), passing
+ * a getter for the element — the element itself is bound later, so a getter is
+ * the only way to hand it over from the top of `<script>`.
+ *
+ *   let scroller: HTMLElement | undefined = $state();
+ *   useScrollRestore(() => scroller, "library");
+ *   …
+ *   <div bind:this={scroller} class="flex-1 overflow-y-auto">
+ *
+ * Memories are keyed by container id and held at module scope, not per call.
+ * Two containers must never share one (the root, home and library scrollers
+ * hold different content for the same URL, so a shared map would restore one
+ * into another) — but a container that *remounts* has to find its offsets again
+ * when it comes back. The home scroller is destroyed on every navigation away,
+ * so a memory owned by the component instance would be empty on return and Back
+ * could only ever land at the top.
+ *
+ * TRACES: UR-072 | DR-156
+ */
+
+import { beforeNavigate, afterNavigate } from "$app/navigation";
+import { tick } from "svelte";
+import { ScrollMemory, classifyNavigation, scrollKey } from "./scrollRestore";
+
+/** Container id → its offsets. Outlives the components that mount them. */
+const memories = new Map<string, ScrollMemory>();
+
+function memoryFor(containerId: string): ScrollMemory {
+  let memory = memories.get(containerId);
+  if (!memory) {
+    memory = new ScrollMemory();
+    memories.set(containerId, memory);
+  }
+  return memory;
+}
+
+/** Forget every container's offsets. For sign-out and tests. */
+export function clearScrollMemories(): void {
+  memories.clear();
+}
+
+export function useScrollRestore(
+  getElement: () => HTMLElement | null | undefined,
+  containerId: string
+): void {
+  const memory = memoryFor(containerId);
+
+  // Record where we were before the route changes. `nav.from` is absent on the
+  // very first navigation, which is exactly when there is nothing to save.
+  beforeNavigate((nav) => {
+    const element = getElement();
+    if (!element || !nav.from) return;
+    memory.save(scrollKey(nav.from.url), element.scrollTop);
+  });
+
+  afterNavigate(async (nav) => {
+    const target = nav.to;
+    if (!target) return;
+
+    const action = memory.decide(scrollKey(target.url), classifyNavigation(nav));
+    if (action.kind === "none") return;
+
+    const top = action.kind === "restore" ? action.top : 0;
+
+    // Wait for the new route's markup to be in the DOM before moving the
+    // scroller — setting scrollTop past the current content height is clamped,
+    // and a reset applied too early is undone by the incoming render.
+    await tick();
+    const element = getElement();
+    if (!element) return;
+
+    element.scrollTop = top;
+
+    // A restore often targets content that is still loading (a library grid
+    // fetches after mount), so the offset would clamp to a short page. Re-apply
+    // on the next frame, once, which is enough for the common case without
+    // fighting a user who has already started scrolling.
+    if (action.kind === "restore" && top > 0) {
+      requestAnimationFrame(() => {
+        const el = getElement();
+        if (el && el.scrollTop < top) el.scrollTop = top;
+      });
+    }
+  });
+}

src/lib/utils/scrollRestore.test.ts

@@ -0,0 +1,79 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { ScrollMemory, classifyNavigation } from "./scrollRestore";
+
+describe("classifyNavigation", () => {
+  it("treats the initial page load as an entry", () => {
+    expect(classifyNavigation({ type: "enter" })).toBe("enter");
+  });
+
+  it("treats back/forward gestures as a popstate", () => {
+    expect(classifyNavigation({ type: "popstate" })).toBe("popstate");
+  });
+
+  it("treats link and goto navigations as forward moves", () => {
+    expect(classifyNavigation({ type: "link" })).toBe("forward");
+    expect(classifyNavigation({ type: "goto" })).toBe("forward");
+    expect(classifyNavigation({ type: "form" })).toBe("forward");
+  });
+});
+
+describe("ScrollMemory", () => {
+  let memory: ScrollMemory;
+
+  beforeEach(() => {
+    memory = new ScrollMemory();
+  });
+
+  // The bug: a scroll container that lives in a persistent layout keeps its
+  // offset across a forward navigation, so a page opened from a scrolled list
+  // starts part-way down. A forward move must always land at the top.
+  it("resets to the top on a forward navigation, even from a scrolled page", () => {
+    memory.save("/library", 1200);
+
+    expect(memory.decide("/library/abc123", "forward")).toEqual({ kind: "reset" });
+  });
+
+  it("resets to the top when navigating forward to a page seen before", () => {
+    memory.save("/library", 1200);
+    memory.save("/search", 340);
+
+    // Re-entering /library by tapping a nav link is a fresh visit, not a Back.
+    expect(memory.decide("/library", "forward")).toEqual({ kind: "reset" });
+  });
+
+  it("restores the saved offset on Back", () => {
+    memory.save("/library", 1200);
+
+    expect(memory.decide("/library", "popstate")).toEqual({ kind: "restore", top: 1200 });
+  });
+
+  it("restores the top when Back targets a page with no saved offset", () => {
+    expect(memory.decide("/library", "popstate")).toEqual({ kind: "restore", top: 0 });
+  });
+
+  it("keeps offsets per route rather than sharing one across pages", () => {
+    memory.save("/library", 1200);
+    memory.save("/search", 340);
+
+    expect(memory.decide("/library", "popstate")).toEqual({ kind: "restore", top: 1200 });
+    expect(memory.decide("/search", "popstate")).toEqual({ kind: "restore", top: 340 });
+  });
+
+  it("leaves the container alone on the initial load", () => {
+    expect(memory.decide("/", "enter")).toEqual({ kind: "none" });
+  });
+
+  it("overwrites a stale offset when the same route is saved again", () => {
+    memory.save("/library", 1200);
+    memory.save("/library", 80);
+
+    expect(memory.decide("/library", "popstate")).toEqual({ kind: "restore", top: 80 });
+  });
+
+  it("forgets nothing on decide, so a repeated Back still restores", () => {
+    memory.save("/library", 1200);
+
+    memory.decide("/library", "popstate");
+    expect(memory.decide("/library", "popstate")).toEqual({ kind: "restore", top: 1200 });
+  });
+});

src/lib/utils/scrollRestore.ts

@@ -0,0 +1,91 @@
+/**
+ * Per-route scroll memory for the app's persistent scroll containers.
+ *
+ * The shell keeps its scrollers alive across navigation on purpose: the root
+ * layout, the home page and the library layout each own a
+ * `flex-1 overflow-y-auto` box that outlives the route rendered inside it. That
+ * is what makes the bottom UI a flex sibling rather than a measured overlay —
+ * but it also means the *element* never remounts, so its `scrollTop` survives a
+ * route change and the next page opens part-way down.
+ *
+ * SvelteKit's own scroll restoration cannot help here: it saves and restores
+ * `window` scroll, and in this app the window never scrolls at all.
+ *
+ * So each container gets its own memory, which reproduces normal browser
+ * behaviour:
+ *
+ *  - **forward** (link/goto/form) — a fresh visit, always lands at the top;
+ *  - **popstate** (hardware/gesture Back or Forward) — restores the offset the
+ *    route was left at, so Back out of a detail page returns you to your place
+ *    in the list rather than to the top of it;
+ *  - **enter** (initial load) — left alone; there is nothing to leak yet.
+ *
+ * The decision is pure and lives here so it can be unit-tested without a DOM;
+ * `scrollContainer.svelte.ts` is the thin action that applies it.
+ *
+ * TRACES: UR-054 | DR-156
+ */
+
+/** How a navigation should affect a persistent scroll container. */
+export type NavKind = "enter" | "popstate" | "forward";
+
+/** What to do with the container once the new route has rendered. */
+export type ScrollAction =
+  | { kind: "reset" }
+  | { kind: "restore"; top: number }
+  | { kind: "none" };
+
+/**
+ * Collapse SvelteKit's navigation types into the three cases that matter.
+ *
+ * `enter` is the initial load. `popstate` is a Back/Forward gesture. Everything
+ * else — `link`, `goto`, `form` — is a forward move into a new page.
+ */
+export function classifyNavigation(nav: { type?: string | null }): NavKind {
+  if (nav.type === "enter") return "enter";
+  if (nav.type === "popstate") return "popstate";
+  return "forward";
+}
+
+/**
+ * Remembers the offset each route was left at, for one scroll container.
+ *
+ * One instance per container: the root scroller, the home scroller and the
+ * library scroller hold different content for the same URL, so a shared map
+ * would restore one container's offset into another.
+ */
+export class ScrollMemory {
+  #offsets = new Map<string, number>();
+
+  /** Record where `key` was scrolled to, before we navigate away from it. */
+  save(key: string, top: number): void {
+    this.#offsets.set(key, Math.max(0, top));
+  }
+
+  /**
+   * Decide what the container should do on arriving at `key`.
+   *
+   * Note this does not consume the saved offset: a route can be returned to
+   * more than once, and each Back should restore the same place.
+   */
+  decide(key: string, kind: NavKind): ScrollAction {
+    if (kind === "enter") return { kind: "none" };
+    if (kind === "popstate") return { kind: "restore", top: this.#offsets.get(key) ?? 0 };
+    return { kind: "reset" };
+  }
+
+  /** Drop everything. Intended for tests and sign-out. */
+  clear(): void {
+    this.#offsets.clear();
+  }
+}
+
+/**
+ * The memory key for a URL.
+ *
+ * Path plus query: a library grid filtered by genre is a different list from
+ * the unfiltered one, and returning to it should restore its own place.
+ */
+export function scrollKey(url: { pathname: string; search?: string }): string {
+  return `${url.pathname}${url.search ?? ""}`;
+}