feat(player): the YouTube player and the file viewer are named in the address

The player names what it plays in its own history entry (watch, wrel, wtab): a reload or a
bookmark reopens it on the page that hosts it, with that page's list as the queue, or alone
from the catalog (GET /api/videos/{id}/row); a page that hosts none gets the shell's. Back
lands on the page's address without it (useBackToClose's url; ui/Modal passes it on). The
Files viewer and player do the same (fview, fplay). The Plex and channel-manager views are
always written in full, as their fallback is remembered state.

backend/app/routes/feed.py

@@ -249,6 +249,21 @@ def set_video_progress(
     return {"ok": True, "video_id": video_id, "position_seconds": position}
 
 
+@router.get("/videos/{video_id}/row")
+def get_video_row(
+    video_id: str = Path(max_length=32),
+    user: User = Depends(current_user),
+    db: Session = Depends(get_db),
+) -> dict:
+    """One catalog video as the feed lists it (its channel, this user's watch state and resume point,
+    saved): what a player opened from an address starts from. The catalog only, so it costs nothing;
+    every video a player can open (a list's row, a related one) is in it."""
+    rows = queries.feed_rows_by_ids(db, user, [video_id])
+    if not rows:
+        raise not_found("video")
+    return rows[0]
+
+
 @router.get("/videos/{video_id}")
 def get_video_detail(
     video_id: str,

backend/tests/test_video_row.py

@@ -0,0 +1,47 @@
+"""A catalog video as the feed lists it, the row a player opened from an address starts from. DB lane."""
+
+from datetime import datetime, timezone
+
+from app.catalog.models import Channel, Video
+from app.reader.models import VideoState
+
+
+def _video(db, vid="v1"):
+    db.add(Channel(id="UCo", title="Owner", handle="@owner"))
+    db.flush()
+    db.add(
+        Video(
+            id=vid,
+            title="A talk",
+            channel_id="UCo",
+            published_at=datetime.now(timezone.utc),
+            duration_seconds=3600,
+        )
+    )
+    db.commit()
+
+
+def test_a_video_comes_as_the_feed_row_with_my_own_state(db, make_user, as_user):
+    me, other = make_user(), make_user()
+    _video(db)
+    db.add(VideoState(user_id=me.id, video_id="v1", status="new", position_seconds=600))
+    db.add(VideoState(user_id=other.id, video_id="v1", status="watched", position_seconds=90))
+    db.commit()
+    r = as_user(me).get("/api/videos/v1/row")
+    assert r.status_code == 200, r.text
+    row = r.json()
+    assert (row["id"], row["title"], row["channel_title"]) == ("v1", "A talk", "Owner")
+    assert (row["status"], row["position_seconds"]) == ("new", 600)
+    assert row["watch_url"] == "https://www.youtube.com/watch?v=v1"
+
+
+def test_a_video_never_opened_has_no_state(db, make_user, as_user):
+    _video(db)
+    row = as_user(make_user()).get("/api/videos/v1/row").json()
+    assert (row["status"], row["position_seconds"], row["saved"]) == ("new", 0, False)
+
+
+def test_a_video_outside_the_catalog_is_not_found(db, make_user, as_user):
+    r = as_user(make_user()).get("/api/videos/nope/row")
+    assert r.status_code == 404
+    assert r.json()["detail"]["code"] == "not_found"

frontend/src/components/ui/Modal.tsx

@@ -65,6 +65,7 @@ export default function Modal({
   placement = "center",
   initialFocus,
   headerActions,
+  url,
 }: {
   title: ReactNode;
   initialFocus: ModalFocus;
@@ -81,10 +82,14 @@ export default function Modal({
   placement?: "center" | "drawer" | "drawer-start" | "top";
   /** Controls beside the ✕ in the header (a side panel's pin and customize, C2). */
   headerActions?: ReactNode;
+  /** What the dialog names in the address while it is open, when it is part of the view (a viewer, a
+   *  player): written into its own history entry, so a reload or a bookmark reopens it and Back lands
+   *  on the address without it (lib/history). */
+  url?: Record<string, string | null>;
 }) {
   const { t } = useTranslation();
   // Browser/mouse Back closes the topmost modal instead of navigating away.
-  useBackToClose(onClose);
+  useBackToClose(onClose, url);
   // ONE container element for the dialog's whole life, re-parented between <body> and the fullscreen
   // element — and attached before the children commit, so an `autoFocus` child
   // still gets the focus. Both rules live in the hook; `ui/AnchoredPopover` shares it.

frontend/src/features/navigation/NavigationProvider.dom.test.tsx

@@ -28,6 +28,7 @@ vi.mock("react-i18next", async (importOriginal) => {
 import { NavigationProvider } from "./NavigationProvider";
 import { useNavigation, useNavigationActions } from "./navigationContext";
 import { urlPage } from "./urlPage";
+import { channelUrl } from "../../lib/urlState";
 import { useBackToClose } from "../../lib/history";
 import { PageHeading } from "../../components/ui/Headings";
 
@@ -280,6 +281,22 @@ describe("NavigationProvider · the channel page's address", () => {
   });
 });
 
+// The YouTube player opens over any page and names itself in its own entry (lib/playerUrlState).
+describe("NavigationProvider · the player's address", () => {
+  it("a page switch takes a player the address still names with it", () => {
+    window.history.replaceState({}, "", "/?q=music&watch=v1&wrel=v2&wtab=related");
+    const { result } = render();
+    act(() => result.current.setPage("stats"));
+    expect(window.location.search).toBe("?page=stats");
+  });
+
+  it("a channel link names no player: opening the channel closes it", () => {
+    window.history.replaceState({}, "", "/?q=music&watch=v1&wrel=v2&wtab=related");
+    render();
+    expect(channelUrl("UC1")).toBe("/?chan=UC1");
+  });
+});
+
 describe("NavigationProvider · Back", () => {
   // A tab that had a since-removed module open, reloaded onto the new build: its older history
   // entries still name that page, and Back lands on one of them.

frontend/src/features/navigation/NavigationProvider.tsx

@@ -20,6 +20,7 @@ import {
 } from "../../lib/history";
 import { foreignUrlKeys, moduleUrlKeys, pageTitleKey, reachablePage } from "./moduleRegistry";
 import { CHANNEL_PAGE_KEYS } from "../../lib/channelPageUrlState";
+import { PLAYER_KEYS } from "../../lib/playerUrlState";
 import {
   channelViewFrom,
   loadInitialPage,
@@ -43,12 +44,14 @@ import {
 //
 // The contexts, their value types and the hooks live in navigationContext.ts.
 
-/** The address bar of `page`'s root: the page (feed implicit) with every module's own keys cleared — a
- *  page switch resets to that module's root, and its store mirrors what it holds back in. */
+/** The address bar of `page`'s root: the page (feed implicit), no channel or player over it, and every
+ *  module's own keys cleared — a page switch resets to that module's root, and its store mirrors what
+ *  it holds back in. */
 function pageRootParams(page: Page): Record<string, string | null> {
   return {
     page: page === "feed" ? null : page,
     ...closedChannelParams(),
+    ...nulls(PLAYER_KEYS),
     ...nulls(moduleUrlKeys()),
   };
 }

frontend/src/features/player/LinkedPlayer.tsx

@@ -0,0 +1,40 @@
+import { lazy, Suspense, useState } from "react";
+import { useTranslation } from "react-i18next";
+import { useQueryClient } from "@tanstack/react-query";
+import { type Video, type VideoStatus } from "../../lib/api";
+import { qk } from "../../lib/queryKeys";
+import { notifyActionError } from "../../lib/actionErrors";
+import { useStableCallback } from "../../lib/useLatest";
+import { writeVideoState } from "../video/videoWrites";
+import { useOpenLinkedPlayer } from "./useOpenLinkedPlayer";
+
+const PlayerModal = lazy(() => import("./PlayerModal"));
+
+/** The shell's player, for an address that names one over a page that hosts none of its own (the
+ *  channel manager, where the watched-videos dialog played it; any page a link names): the video
+ *  alone. Decided at boot, once — `hosted` is whether the page on screen then opens it itself. */
+export function LinkedPlayer({ hosted }: { hosted: boolean }) {
+  const { t } = useTranslation();
+  const qc = useQueryClient();
+  const [own] = useState(!hosted);
+  const [video, setVideo] = useState<Video | null>(null);
+  useOpenLinkedPlayer(
+    own,
+    () => undefined,
+    (v) => setVideo(v),
+  );
+  const onState = useStableCallback((id: string, status: VideoStatus) => {
+    const write = writeVideoState(qc, id, status);
+    write
+      .then(() => qc.invalidateQueries({ queryKey: qk.feed() }))
+      .catch((e: unknown) => notifyActionError(e, t("errors.writeFailed.videoState")));
+    return write;
+  });
+  const close = useStableCallback(() => setVideo(null));
+  if (!video) return null;
+  return (
+    <Suspense fallback={null}>
+      <PlayerModal video={video} startAt={null} onClose={close} onState={onState} />
+    </Suspense>
+  );
+}

frontend/src/features/player/PlayerModal.dom.test.tsx

@@ -111,6 +111,7 @@ function renderModal(ui: ReactNode) {
 afterEach(() => {
   cleanup();
   vi.restoreAllMocks();
+  window.history.replaceState(null, "", "/");
   started.length = 0;
   loaded.length = 0;
   seeks.length = 0;

frontend/src/features/player/PlayerModal.tsx

@@ -68,6 +68,7 @@ import {
 import { canFullscreenElements, fullscreenElement } from "../../lib/fullscreen";
 import { dispatch, isActivationTarget, setScopeCoveredProbe, useKeyScope } from "../../lib/keymap";
 import { useBackToClose } from "../../lib/history";
+import { linkedPlayer, playerParamUpdates, type PlayerPanelTab } from "../../lib/playerUrlState";
 import ChannelNameLink from "../video/ChannelNameLink";
 import Toaster from "../../components/ui/Toaster";
 import { useOverlayOrder } from "../../components/ui/overlayOrder";
@@ -222,8 +223,6 @@ export default function PlayerModal({
   const { openChannel } = useNavigationActions();
   const qc = useQueryClient();
   const { ref: descFadeRef, style: descFadeStyle } = useScrollFade();
-  // Browser/mouse Back closes the player instead of leaving the page.
-  useBackToClose(onClose);
   // Freeze the launch queue: the player steps through the SAME filtered + sorted list it was
   // opened with, for its whole session. The live feed refetches and reorders/drops items under
   // us — e.g. auto-marking each video watched near its end removes it from a filtered feed — which
@@ -277,6 +276,25 @@ export default function PlayerModal({
     setRelatedOf(active.id);
     setRelated(null);
   }
+  // An address that names the item this player opens on (a reload, a bookmark) names its view too: the
+  // related video playing in place over it and the panel's tab come back with it. Read once.
+  const [linked] = useState(() => {
+    const here = linkedPlayer();
+    return here && here.watch === video.id ? here : null;
+  });
+  const linkedRelated = useQuery({
+    queryKey: qk.videoRow(linked?.related ?? ""),
+    queryFn: () => api.videoRow(linked!.related!),
+    enabled: !!linked?.related,
+    retry: false,
+  });
+  const [relatedAdopted, setRelatedAdopted] = useState(false);
+  if (!relatedAdopted && linkedRelated.data) {
+    setRelatedAdopted(true);
+    // Only over the item it was named with: a step of the queue before it arrived left that one.
+    if (active.id === linked?.watch && !related)
+      setRelated({ video: linkedRelated.data, startAt: null });
+  }
   const subject = related?.video ?? active;
   const subjectResume = related
     ? (related.startAt ?? related.video.position_seconds ?? 0)
@@ -753,7 +771,7 @@ export default function PlayerModal({
   // take the side panel's place of the description, a tab beside it; stacked, a drawer over the video
   // opened from a button beside the ⓘ. The list is the OPENED video's: one played from it leaves the
   // list in place, to try the next one (the owner's pick).
-  const [panelTab, setPanelTab] = useState<"description" | "related">("description");
+  const [panelTab, setPanelTab] = useState<PlayerPanelTab>(linked?.panel ?? "description");
   const [relatedOpen, setRelatedOpen] = useState(false);
   // The drawer is the stacked layout's: going wide while it is open, the list moves into the panel's
   // tab instead. Left open, it reopened unasked when the window narrowed again.
@@ -762,6 +780,17 @@ export default function PlayerModal({
     setPanelTab("related");
   }
   const panelTabs = useTabPanel();
+  // Browser/mouse Back closes the player instead of leaving the page. Its entry's address names what
+  // it plays (the queue's item, a related one over it) and the wide panel's tab, so a reload or a
+  // bookmark reopens it as it is; the page's own entry under it never carries them.
+  useBackToClose(
+    onClose,
+    playerParamUpdates({
+      watch: active.id,
+      related: related?.video.id ?? null,
+      panel: wide ? panelTab : "description",
+    }),
+  );
   // Turned off on this instance (a daily limit of 0): no tab, no button — nothing that could only
   // be refused.
   const relatedOn = useMe().related_enabled;

frontend/src/features/player/PlayerModal.url.dom.test.tsx

@@ -0,0 +1,180 @@
+// @vitest-environment jsdom
+//
+// The URL is the view: the YouTube player names what it plays in its own history entry — the item of
+// the queue, a related video played in place over it, the wide panel's tab — so a reload or a bookmark
+// reopens it as it was, and Back lands on the page's address without it. Its own file: the overlay
+// history is module state, and these read the address the closed players of other tests step back over.
+//
+// `window.YT` is a fake installed before the player's API loader first runs (see PlayerModal.dom.test).
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import { act, fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+vi.mock("react-i18next", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("react-i18next")>()),
+  useTranslation: () => ({ t: (k: string) => k, i18n: { language: "en" } }),
+}));
+vi.mock("../navigation/navigationContext", () => ({
+  useNavigationActions: () => ({ openChannel: vi.fn() }),
+}));
+vi.mock("../video/AddToPlaylist", () => ({ default: () => null }));
+vi.mock("../downloads/DownloadButton", () => ({ default: () => null }));
+
+import PlayerModal from "./PlayerModal";
+import { api, type Me, type Video } from "../../lib/api";
+import { qk } from "../../lib/queryKeys";
+
+beforeAll(() => {
+  class Stub {
+    observe() {}
+    unobserve() {}
+    disconnect() {}
+    takeRecords() {
+      return [];
+    }
+  }
+  globalThis.ResizeObserver ??= Stub as unknown as typeof ResizeObserver;
+  globalThis.IntersectionObserver ??= Stub as unknown as typeof IntersectionObserver;
+});
+
+const started: { videoId: string; start: number | undefined }[] = [];
+let playerEvents: { onReady?: () => void } = {};
+const fakePlayer = new Proxy(
+  { getCurrentTime: () => 0, getDuration: () => 3000, getVideoData: () => null },
+  { get: (t, k) => (k in t ? t[k as keyof typeof t] : k === "then" ? undefined : () => undefined) },
+);
+window.YT = {
+  Player: function (
+    _el: unknown,
+    opts: { videoId: string; playerVars: { start?: number }; events?: typeof playerEvents },
+  ) {
+    started.push({ videoId: opts.videoId, start: opts.playerVars.start });
+    playerEvents = opts.events ?? {};
+    return fakePlayer;
+  } as never,
+};
+const lastStart = () => started[started.length - 1];
+
+const vid = (id: string, position_seconds = 0): Video =>
+  ({
+    id,
+    title: `Video ${id}`,
+    channel_id: "UCx",
+    channel_title: "Channel",
+    status: "new",
+    position_seconds,
+    duration_seconds: 3000,
+    watch_url: `https://www.youtube.com/watch?v=${id}`,
+  }) as unknown as Video;
+const related = (id: string, position_seconds = 0) => ({
+  ...vid(id, position_seconds),
+  followed: false,
+});
+
+// The wide layout (the side panel with its tabs): jsdom has no matchMedia, so one is put in.
+function wideWindow() {
+  window.matchMedia = ((q: string) => ({
+    matches: q === "(min-width: 1280px)",
+    media: q,
+    addEventListener: () => {},
+    removeEventListener: () => {},
+  })) as unknown as typeof window.matchMedia;
+}
+
+function renderModal(video: Video, queue: Video[]) {
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  qc.setQueryData(qk.me(), { related_enabled: true } as Me);
+  return render(
+    <QueryClientProvider client={qc}>
+      <PlayerModal
+        video={video}
+        queue={queue}
+        onClose={() => {}}
+        onState={() => Promise.resolve()}
+      />
+    </QueryClientProvider>,
+  );
+}
+
+// A closed player steps back over its entry a task later (jsdom's back(), like a browser's).
+async function closeAndLand(unmount: () => void) {
+  const landed = new Promise((r) => window.addEventListener("popstate", r, { once: true }));
+  unmount();
+  await act(() => landed);
+}
+
+const here = () => new URLSearchParams(window.location.search);
+
+beforeEach(() => {
+  vi.spyOn(api, "videoDetail").mockReturnValue(new Promise(() => {}));
+  vi.spyOn(api, "related").mockResolvedValue({
+    items: [related("rel1"), related("rel2", 120)],
+    has_more: false,
+    next_cursor: null,
+  });
+});
+afterEach(() => {
+  vi.restoreAllMocks();
+  delete (window as { matchMedia?: unknown }).matchMedia;
+  started.length = 0;
+});
+
+describe("the player's address", () => {
+  it("names the item playing now in its own entry, a step of the queue too", async () => {
+    window.history.replaceState({ sfPage: "feed" }, "", "/?q=talks");
+    const r = renderModal(vid("A"), [vid("A"), vid("B")]);
+    await waitFor(() => expect(here().get("watch")).toBe("A"));
+    expect(here().get("q")).toBe("talks");
+    fireEvent.click(screen.getAllByRole("button", { name: "player.next" })[0]!);
+    await waitFor(() => expect(here().get("watch")).toBe("B"));
+    await closeAndLand(r.unmount);
+    expect(window.location.search).toBe("?q=talks");
+  });
+
+  it("wide: names the related video playing over it and the panel's tab, and Back drops it", async () => {
+    wideWindow();
+    window.history.replaceState({ sfPage: "feed" }, "", "/");
+    const r = renderModal(vid("A", 40), [vid("A", 40)]);
+    act(() => playerEvents.onReady?.());
+    fireEvent.click(screen.getByRole("tab", { name: "player.related.title" }));
+    await waitFor(() => expect(here().get("wtab")).toBe("related"));
+    const rows = await screen.findAllByRole("link", { name: "Video rel2" });
+    fireEvent.click(rows.find((a) => a.hasAttribute("data-nav-open"))!);
+    await waitFor(() => expect(here().get("wrel")).toBe("rel2"));
+    expect(here().get("watch")).toBe("A");
+    fireEvent.click(screen.getByRole("button", { name: "player.back" }));
+    await waitFor(() => expect(here().has("wrel")).toBe(false));
+    expect(here().get("watch")).toBe("A");
+    await closeAndLand(r.unmount);
+    expect(window.location.search).toBe("");
+  });
+
+  it("wide: a link's related video and panel tab come back over the item it names", async () => {
+    wideWindow();
+    window.history.replaceState({ sfPage: "feed" }, "", "/?watch=A&wrel=rel2&wtab=related");
+    const row = vi.spyOn(api, "videoRow").mockResolvedValue(vid("rel2", 120));
+    const r = renderModal(vid("A", 40), [vid("A", 40)]);
+    await waitFor(() => expect(lastStart()).toEqual({ videoId: "rel2", start: 120 }));
+    expect(row).toHaveBeenCalledWith("rel2");
+    const tab = screen.getByRole("tab", { name: "player.related.title" });
+    expect(tab.getAttribute("aria-selected")).toBe("true");
+    expect(screen.getByRole("button", { name: "player.back" })).toBeTruthy();
+    expect(here().get("wrel")).toBe("rel2");
+    await closeAndLand(r.unmount);
+    // The entry the link opened at named the player; once the player is gone, so is its name.
+    expect(window.location.search).toBe("");
+  });
+
+  it("wide: a link naming another item brings none of its view", async () => {
+    wideWindow();
+    window.history.replaceState({ sfPage: "feed" }, "", "/?watch=Z&wrel=rel2&wtab=related");
+    const row = vi.spyOn(api, "videoRow").mockResolvedValue(vid("rel2", 120));
+    const r = renderModal(vid("A", 40), [vid("A", 40)]);
+    await waitFor(() => expect(here().get("watch")).toBe("A"));
+    expect(row).not.toHaveBeenCalled();
+    expect(here().has("wrel")).toBe(false);
+    expect(here().has("wtab")).toBe(false);
+    expect(lastStart()?.videoId).toBe("A");
+    await closeAndLand(r.unmount);
+  });
+});

frontend/src/features/player/useOpenLinkedPlayer.dom.test.tsx

@@ -0,0 +1,109 @@
+// @vitest-environment jsdom
+//
+// A reload or a bookmark of the YouTube player reopens it: the page that hosts it opens it once its list
+// is in — from the list, so it plays on through it, or alone from the catalog — and a page that hosts
+// none gets the shell's, the video alone. A video the catalog no longer has is said, not swallowed.
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { cleanup, render, renderHook, screen, waitFor } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import type { ReactNode } from "react";
+
+vi.mock("react-i18next", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("react-i18next")>()),
+  useTranslation: () => ({ t: (k: string) => k, i18n: { language: "en" } }),
+}));
+vi.mock("../../lib/actionErrors", () => ({ notifyActionError: vi.fn() }));
+// The player itself is not what is under test: it shows what it was opened on.
+vi.mock("./PlayerModal", () => ({
+  default: ({ video, queue }: { video: Video; queue?: Video[] }) => (
+    <p>
+      playing {video.id} {queue ? "in a list" : "alone"}
+    </p>
+  ),
+}));
+
+import { useOpenLinkedPlayer } from "./useOpenLinkedPlayer";
+import { LinkedPlayer } from "./LinkedPlayer";
+import { api, type Video } from "../../lib/api";
+import { notifyActionError } from "../../lib/actionErrors";
+
+const vid = (id: string) => ({ id, title: id }) as unknown as Video;
+
+function wrapper({ children }: { children: ReactNode }) {
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  return <QueryClientProvider client={qc}>{children}</QueryClientProvider>;
+}
+
+afterEach(() => {
+  cleanup();
+  vi.restoreAllMocks();
+  vi.mocked(notifyActionError).mockClear();
+  window.history.replaceState(null, "", "/");
+});
+
+describe("useOpenLinkedPlayer", () => {
+  it("opens the item from the host's list once the list is in, and only once", async () => {
+    window.history.replaceState(null, "", "/?watch=B");
+    const row = vi.spyOn(api, "videoRow");
+    const open = vi.fn();
+    const list = [vid("A"), vid("B")];
+    const { rerender } = renderHook(
+      ({ ready }) => useOpenLinkedPlayer(ready, (id) => list.find((v) => v.id === id), open),
+      { wrapper, initialProps: { ready: false } },
+    );
+    expect(open).not.toHaveBeenCalled();
+    rerender({ ready: true });
+    await waitFor(() => expect(open).toHaveBeenCalledWith(list[1], true));
+    rerender({ ready: true });
+    expect(open).toHaveBeenCalledTimes(1);
+    expect(row).not.toHaveBeenCalled();
+  });
+
+  it("opens an item the list does not hold alone, its row from the catalog", async () => {
+    window.history.replaceState(null, "", "/?watch=Z");
+    vi.spyOn(api, "videoRow").mockResolvedValue(vid("Z"));
+    const open = vi.fn();
+    renderHook(() => useOpenLinkedPlayer(true, () => undefined, open), { wrapper });
+    await waitFor(() => expect(open).toHaveBeenCalledWith(vid("Z"), false));
+  });
+
+  it("says so when the catalog no longer has it", async () => {
+    window.history.replaceState(null, "", "/?watch=Z");
+    const gone = new Error("not found");
+    vi.spyOn(api, "videoRow").mockRejectedValue(gone);
+    const open = vi.fn();
+    renderHook(() => useOpenLinkedPlayer(true, () => undefined, open), { wrapper });
+    await waitFor(() =>
+      expect(notifyActionError).toHaveBeenCalledWith(gone, "player.linkedFailed"),
+    );
+    expect(open).not.toHaveBeenCalled();
+  });
+
+  it("opens nothing, and asks for nothing, for an address that names no player", async () => {
+    window.history.replaceState(null, "", "/?q=talks");
+    const row = vi.spyOn(api, "videoRow");
+    const open = vi.fn();
+    renderHook(() => useOpenLinkedPlayer(true, () => undefined, open), { wrapper });
+    await new Promise((r) => setTimeout(r, 20));
+    expect(open).not.toHaveBeenCalled();
+    expect(row).not.toHaveBeenCalled();
+  });
+});
+
+describe("the shell's LinkedPlayer", () => {
+  it("plays the video alone over a page that hosts no player", async () => {
+    window.history.replaceState(null, "", "/?page=channels&watch=Z");
+    vi.spyOn(api, "videoRow").mockResolvedValue(vid("Z"));
+    render(<LinkedPlayer hosted={false} />, { wrapper });
+    expect(await screen.findByText("playing Z alone")).toBeTruthy();
+  });
+
+  it("leaves it to a page that hosts its own", async () => {
+    window.history.replaceState(null, "", "/?watch=Z");
+    const row = vi.spyOn(api, "videoRow").mockResolvedValue(vid("Z"));
+    render(<LinkedPlayer hosted />, { wrapper });
+    await new Promise((r) => setTimeout(r, 20));
+    expect(row).not.toHaveBeenCalled();
+    expect(screen.queryByText(/playing/)).toBeNull();
+  });
+});

frontend/src/features/player/useOpenLinkedPlayer.ts

@@ -0,0 +1,39 @@
+import { useEffect, useEffectEvent, useRef, useState } from "react";
+import { useTranslation } from "react-i18next";
+import { useQuery } from "@tanstack/react-query";
+import { api, type Video } from "../../lib/api";
+import { qk } from "../../lib/queryKeys";
+import { linkedPlayer } from "../../lib/playerUrlState";
+import { notifyActionError } from "../../lib/actionErrors";
+
+/** Opens the player an address names (a reload, a bookmark — lib/playerUrlState) on the page that
+ *  hosts it, once: read as the host mounts, opened once its list is in (`ready`). From the list when the
+ *  item is in it (`find`), so the player plays on through the list; else alone, its row fetched from
+ *  the catalog. A row the catalog no longer has is said, not swallowed. */
+export function useOpenLinkedPlayer(
+  ready: boolean,
+  find: (id: string) => Video | undefined,
+  open: (video: Video, inList: boolean) => void,
+): void {
+  const { t } = useTranslation();
+  const [linked] = useState(() => linkedPlayer()?.watch ?? null);
+  // Opened (or said to be gone) once; a ref, as nothing on screen reads it.
+  const done = useRef(linked == null);
+  const listed = ready && linked != null ? find(linked) : undefined;
+  const row = useQuery({
+    queryKey: qk.videoRow(linked ?? ""),
+    queryFn: () => api.videoRow(linked!),
+    enabled: ready && linked != null && !listed,
+    retry: false,
+  });
+  const openIt = useEffectEvent(open);
+  const failed = useEffectEvent((err: unknown) => notifyActionError(err, t("player.linkedFailed")));
+  useEffect(() => {
+    if (done.current) return;
+    if (listed) openIt(listed, true);
+    else if (row.data) openIt(row.data, false);
+    else if (row.isError) failed(row.error);
+    else return;
+    done.current = true;
+  }, [listed, row.data, row.isError, row.error]);
+}

frontend/src/i18n/locales/en/files.json

@@ -1,4 +1,5 @@
 {
+  "linkedGone": "The file in the address is no longer in this list",
   "navLabel": "Files",
   "searchPlaceholder": "Search files…",
   "count_one": "{{count}} item",

frontend/src/i18n/locales/en/player.json

@@ -1,5 +1,6 @@
 {
   "loading": "Loading…",
+  "linkedFailed": "The video in the address could not be opened",
   "backToOriginal": "Back to the original video",
   "back": "Back",
   "previous": "Previous",

frontend/src/i18n/locales/hu/files.json

@@ -1,4 +1,5 @@
 {
+  "linkedGone": "A címben szereplő fájl már nincs ebben a listában",
   "navLabel": "Fájlok",
   "searchPlaceholder": "Keresés a fájlok között…",
   "count_one": "{{count}} elem",

frontend/src/i18n/locales/hu/player.json

@@ -1,5 +1,6 @@
 {
   "loading": "Betöltés…",
+  "linkedFailed": "A címben szereplő videó nem nyitható meg",
   "backToOriginal": "Vissza az eredeti videóhoz",
   "back": "Vissza",
   "previous": "Előző",

frontend/src/lib/api/feed.ts

@@ -314,6 +314,9 @@ export const feedApi = {
       duration_seconds: Math.floor(durationSeconds),
     }),
   videoDetail: (id: string): Promise<VideoDetail> => req(`/api/videos/${id}`),
+  /** One catalog video as the feed lists it (this user's state with it): what a player opened from an
+   *  address starts from. */
+  videoRow: (id: string): Promise<Video> => req(`/api/videos/${encodeURIComponent(id)}/row`),
   // One file of a Google Takeout export, its bytes as they are; the server tells the two apart.
   takeoutUpload: (file: File): Promise<TakeoutUpload> => uploadReq("/api/takeout", file),
   takeoutStatus: (): Promise<TakeoutStatus> => req("/api/takeout"),

frontend/src/lib/channelsUrlState.dom.test.ts

@@ -36,15 +36,31 @@ describe("channelsParamUpdates", () => {
     expect(channelsParamUpdates({ ...BASE, search: "  " }).cq).toBeNull();
   });
 
-  it("emits nothing for the all-default state", () => {
-    expect(channelsParamUpdates(BASE)).toEqual({ ctab: null, csort: null, cf: null, cq: null });
+  it("writes the default view in full: this browser remembers one a link must not inherit", () => {
+    expect(channelsParamUpdates(BASE)).toEqual({
+      ctab: "subscribed",
+      csort: "none",
+      cf: "",
+      cq: null,
+    });
+  });
+
+  it("a link to the default view opens it over another remembered one", () => {
+    const params = applyUpdates(channelsParamUpdates(BASE));
+    const back = channelsParamsToState(params, {
+      view: "hidden",
+      sort: { key: "subscribers", dir: "desc" },
+      filters: { sync: "fully" },
+      search: "",
+    });
+    expect(back).toEqual(BASE);
   });
 
   it("clears every key when passed null (off-manager page)", () => {
     expect(channelsParamUpdates(null)).toEqual({ ctab: null, csort: null, cf: null, cq: null });
   });
 
-  it("emits only non-default keys", () => {
+  it("writes the view picked", () => {
     const u = channelsParamUpdates({
       view: "hidden",
       sort: { key: "subscribers", dir: "desc" },
@@ -57,8 +73,8 @@ describe("channelsParamUpdates", () => {
     expect(u.cq).toBe("tom");
   });
 
-  it("drops empty filter entries so a cleared funnel emits no cf", () => {
-    expect(channelsParamUpdates({ ...BASE, filters: { tags: [], sync: "" } }).cf).toBeNull();
+  it("drops empty filter entries so a cleared funnel writes an empty cf", () => {
+    expect(channelsParamUpdates({ ...BASE, filters: { tags: [], sync: "" } }).cf).toBe("");
   });
 });
 

frontend/src/lib/channelsUrlState.ts

@@ -2,10 +2,11 @@
 // from the address bar so a manager view is bookmarkable/shareable — the analogue of the feed's
 // urlState and Plex's plexUrlState. Keys are NAMESPACED (`ctab`/`csort`/`cf`) so they're
 // channels-unique (like `?v=`/`?pl`/`pscope`): no other provider ever reads or clears them, and the
-// feed's URL-stripping can't delete them out from under the manager. Only non-default values are
-// emitted, so URLs stay clean. The name search (`cq`) is part of the view like the rest: a bookmark of a
-// searched list opens searched.
-import { decodeSortParam, encodeSortParam, type SortState } from "./columnSort";
+// feed's URL-stripping can't delete them out from under the manager. The tab, sort and filters are
+// always written, their defaults too: a page opened without them takes this browser's remembered view,
+// which may not be the one bookmarked. The name search (`cq`) is part of the view like the rest (a
+// bookmark of a searched list opens searched), but nothing remembers it, so only a term is written.
+import { decodeSortParamOrNone, encodeSortParamOrNone, type SortState } from "./columnSort";
 import { type FilterMap } from "./tableColumns";
 import { decodeFilterMap, encodeFilterMap } from "./filterMapParam";
 
@@ -23,12 +24,11 @@ export const CHANNELS_KEYS = ["ctab", "csort", "cf", "cq"] as const;
 const KEYS = CHANNELS_KEYS;
 const VIEWS = ["subscribed", "discovery", "hidden", "blocked"];
 
-// Sort ⇄ `key:dir` (e.g. `subscribers:desc`) via the shared codec in columnSort. There is no default
-// sort here (fallback null), so any sort emits — no default short-circuit needed. The filter map rides
-// as one JSON value (lib/filterMapParam).
+// Sort ⇄ `key:dir` (e.g. `subscribers:desc`, `none` unsorted) via the shared codec in columnSort. The
+// filter map rides as one JSON value (lib/filterMapParam), an empty one as `cf=`.
 
 /** The address-bar delta for the manager content state: each namespaced key mapped to its emitted
- * value, or null to delete it (so a control back at its default clears the key). Pass `null` to clear
+ * value, or null to delete it (only the search's, when cleared). Pass `null` to clear
  * ALL manager keys — used when the app is off the Channels page (localStorage still holds the state; it
  * re-mirrors on return). Feed the result into urlWithParams(). */
 export function channelsParamUpdates(
@@ -36,9 +36,9 @@ export function channelsParamUpdates(
 ): Record<string, string | null> {
   if (!state) return { ctab: null, csort: null, cf: null, cq: null };
   return {
-    ctab: state.view && state.view !== "subscribed" ? state.view : null,
-    csort: encodeSortParam(state.sort),
-    cf: encodeFilterMap(state.filters),
+    ctab: state.view || "subscribed",
+    csort: encodeSortParamOrNone(state.sort),
+    cf: encodeFilterMap(state.filters) ?? "",
     cq: state.search.trim() || null,
   };
 }
@@ -55,10 +55,10 @@ export function channelsParamsToState(
   base: ChannelsUrlState,
 ): ChannelsUrlState {
   const tab = params.get("ctab");
-  const csort = params.get("csort");
+  const linkedSort = decodeSortParamOrNone(params.get("csort"));
   return {
     view: tab && VIEWS.includes(tab) ? tab : base.view,
-    sort: csort != null ? (decodeSortParam(csort) ?? base.sort) : base.sort,
+    sort: linkedSort === undefined ? base.sort : linkedSort,
     filters: params.has("cf") ? decodeFilterMap(params.get("cf") ?? "") : base.filters,
     search: params.get("cq") ?? base.search,
   };

frontend/src/lib/columnSort.ts

@@ -53,6 +53,22 @@ export function decodeSortParam(raw: string): SortState {
   return parseSortState({ key, dir });
 }
 
+// The list's own order (no column sort) as a word of its own, for a page whose sort is remembered (an
+// account pref, this browser's view): there the sort is always written, because a page opened without
+// one takes the remembered sort, which may not be the one bookmarked.
+const UNSORTED = "none";
+
+export function encodeSortParamOrNone(s: SortState): string {
+  return encodeSortParam(s) ?? UNSORTED;
+}
+
+/** The sort an address names; `undefined` when it names none or a malformed one (the remembered one
+ * applies). */
+export function decodeSortParamOrNone(raw: string | null): SortState | undefined {
+  if (raw == null) return undefined;
+  return raw === UNSORTED ? null : (decodeSortParam(raw) ?? undefined);
+}
+
 /** The header-click cycle: unsorted → ascending → descending → unsorted. */
 export function cycleSort(current: SortState, key: string): SortState {
   if (!current || current.key !== key) return { key, dir: "asc" };

frontend/src/lib/filesUrlState.ts

@@ -1,30 +1,34 @@
-import { decodeSortParam, encodeSortParam, type SortState } from "./columnSort";
-
 // The Files page's address-bar keys: the folder shown (`?folder=`, its encoding in
 // modules/files/filesContext), the file it turns to once (`?item=`), the name search (`?fq=`) and the
-// sort (`?fsort=`). Here, beside the other pages' key lists, so the page's definition can declare them
-// without importing its own folder.
+// sort (`?fsort=`, always written, lib/columnSort's `none` for the list's own order). Here, beside the
+// other pages' key lists, so the page's definition can declare them without importing its own folder.
 export const FILES_FOLDER_KEY = "folder";
 export const FILES_ITEM_KEY = "item";
 export const FILES_SEARCH_KEY = "fq";
 export const FILES_SORT_KEY = "fsort";
+// The file open over the list: in the viewer, or in the player. Each dialog names itself in its own
+// history entry (ui/Modal's `url`), so Back lands on the list's address without it.
+export const FILES_VIEW_KEY = "fview";
+export const FILES_PLAY_KEY = "fplay";
 export const FILES_KEYS = [
   FILES_FOLDER_KEY,
   FILES_ITEM_KEY,
   FILES_SEARCH_KEY,
   FILES_SORT_KEY,
+  FILES_VIEW_KEY,
+  FILES_PLAY_KEY,
 ] as const;
 
-// The list's own order (no column sort) has a word of its own: the sort is always written, because a
-// page opened without one takes the account's remembered sort, which may not be the one bookmarked.
-const UNSORTED = "none";
+export type FilesOpenFile = { open: "view" | "play"; id: number };
 
-export function encodeFilesSort(sort: SortState): string {
-  return encodeSortParam(sort) ?? UNSORTED;
+/** The file an address opens over the list (a reload, a bookmark), or null. */
+export function openFileFrom(params: URLSearchParams): FilesOpenFile | null {
+  for (const [open, key] of [
+    ["play", FILES_PLAY_KEY],
+    ["view", FILES_VIEW_KEY],
+  ] as const) {
+    const id = Number(params.get(key));
+    if (Number.isInteger(id) && id > 0) return { open, id };
   }
-
-/** The sort an address names; `undefined` when it names none (the remembered one applies). */
-export function decodeFilesSort(raw: string | null): SortState | undefined {
-  if (raw == null) return undefined;
-  return raw === UNSORTED ? null : decodeSortParam(raw);
+  return null;
 }

frontend/src/lib/history.overlayUrl.dom.test.tsx

@@ -0,0 +1,88 @@
+// @vitest-environment jsdom
+//
+// An overlay that is part of the view (a player) names itself in its own history entry's address, so a
+// reload or a bookmark opens it — and the entry under it never carries those keys, so Back lands on the
+// page as it was. Driven through jsdom's real history: its back()/forward() land their popstate a
+// task later, like a browser's.
+import { afterEach, describe, expect, it } from "vitest";
+import { act, renderHook } from "@testing-library/react";
+import { useBackToClose } from "./history";
+
+const settle = () =>
+  act(async () => {
+    await Promise.resolve();
+  });
+// Step through the history the way the browser does, and wait for its popstate to land.
+const step = (go: () => void) =>
+  act(async () => {
+    const landed = new Promise((r) => window.addEventListener("popstate", r, { once: true }));
+    go();
+    await landed;
+    await Promise.resolve();
+  });
+const search = () => new URLSearchParams(window.location.search);
+
+/** A player-like overlay whose close really unmounts it, naming `url` in its entry. */
+function mountPlayer(initial: Record<string, string | null>) {
+  const holder: { unmount?: () => void } = {};
+  const r = renderHook(
+    (url: Record<string, string | null>) => useBackToClose(() => holder.unmount?.(), url),
+    { initialProps: initial },
+  );
+  holder.unmount = r.unmount;
+  return r;
+}
+
+afterEach(() => {
+  window.history.replaceState(null, "", "/");
+});
+
+describe("an overlay named in its entry's address", () => {
+  it("is named in its own entry, and Back lands on the address under it without it", async () => {
+    window.history.replaceState({ sfPage: "feed" }, "", "/?q=music");
+    const depth = window.history.length;
+    mountPlayer({ watch: "v1", wtab: null });
+    await settle();
+    expect(window.history.length).toBe(depth + 1);
+    expect(search().get("watch")).toBe("v1");
+    expect(search().get("q")).toBe("music");
+    await step(() => window.history.back());
+    expect(search().has("watch")).toBe(false);
+    expect(search().get("q")).toBe("music");
+  });
+
+  it("follows what it names as it changes", async () => {
+    window.history.replaceState({ sfPage: "feed" }, "", "/?q=music");
+    const r = mountPlayer({ watch: "v1", wtab: null });
+    await settle();
+    r.rerender({ watch: "v2", wtab: "related" });
+    expect(search().get("watch")).toBe("v2");
+    expect(search().get("wtab")).toBe("related");
+    r.rerender({ watch: "v2", wtab: null });
+    expect(search().has("wtab")).toBe(false);
+    await step(() => r.unmount());
+    expect(search().has("watch")).toBe(false);
+    expect(search().get("q")).toBe("music");
+  });
+
+  it("closed by its own control, leaves the entry under it as it was", async () => {
+    window.history.replaceState({ sfPage: "feed" }, "", "/?q=music");
+    const r = mountPlayer({ watch: "v1" });
+    await settle();
+    await step(() => r.unmount());
+    expect(window.location.search).toBe("?q=music");
+  });
+
+  it("an entry that still names it after it closed is cleared once it is the current one", async () => {
+    // A reload under an open player: the entry the new document starts from names the player.
+    window.history.replaceState({ sfPage: "feed" }, "", "/?q=music&watch=v1");
+    const r = mountPlayer({ watch: "v1" });
+    await settle();
+    await step(() => r.unmount());
+    expect(search().has("watch")).toBe(false);
+    // Forward onto the closed player's entry: nothing is open there, so neither is it named.
+    await step(() => window.history.forward());
+    expect(search().has("watch")).toBe(false);
+    expect(search().get("q")).toBe("music");
+  });
+});

frontend/src/lib/history.ts

@@ -6,7 +6,8 @@
 //     a module (e.g. the sign-in card's "forgot password" → sign-in) returns to the parent view first.
 //   - useBackToClose: while an overlay/modal is mounted it occupies one history entry; Back
 //     closes the topmost one. A module-level stack keeps nesting correct — closing one modal by
-//     its own button pops exactly its entry without tripping the modals underneath.
+//     its own button pops exactly its entry without tripping the modals underneath. An overlay
+//     that is part of the view (a player) names itself in its entry's address.
 //
 // setPage() pushes a clean { sfPage } entry (dropping _sub/_ov), so each page starts at its root.
 import { useCallback, useEffect, useEffectEvent, useMemo, useRef, useState } from "react";
@@ -273,8 +274,16 @@ function writeSubEntry<T>(next: T, url: SubviewUrl<T> | undefined): void {
 // both undid the navigation AND closed the dialog above it, and the dead Back press after that (the
 // last two measured in Chrome). With nothing ever buried, the stack and the history agree by
 // construction.
-type Overlay = { token: number; cb: () => void };
+// `url`: the keys an overlay names in the address of its own entry (and of the entries above it).
+type Overlay = { token: number; cb: () => void; url?: OverlayUrl };
+type OverlayUrl = Record<string, string | null>;
 const overlayStack: Overlay[] = [];
+// Every key an overlay has named in this document: an entry carries those of the overlays it stands
+// for and none of the rest. The entry under an overlay is never written with its keys, so Back lands
+// on an address without it; and one that still names a closed overlay (the entry a reload under an
+// open player started from, a Forward onto an entry whose overlay is gone) is cleared once it is
+// the current entry.
+const overlayUrlKeys = new Set<string>();
 let overlayCounter = 0;
 // A plain function, not `++overlayCounter` inline: the React Compiler cannot lower an update of a
 // module variable inside a hook, and skipped the whole hook for it (react-hooks/todo).
@@ -298,7 +307,11 @@ function reconcileHistory(): void {
   const want = overlayStack.length;
   while (historyDepth < want && pendingProgrammatic === 0) {
     historyDepth++;
-    window.history.pushState({ ...window.history.state, _ov: nextOverlayToken() }, "");
+    window.history.pushState(
+      { ...window.history.state, _ov: nextOverlayToken() },
+      "",
+      overlayHref(historyDepth),
+    );
   }
   while (historyDepth > want) {
     historyDepth--;
@@ -308,12 +321,34 @@ function reconcileHistory(): void {
     } else {
       // Nothing of ours below to step back to (see backStaysInDocument): the entry stays, unmarked.
       const { _ov: _drop, ...st } = (window.history.state ?? {}) as Record<string, unknown>;
-      window.history.replaceState(st, "");
+      window.history.replaceState(st, "", overlayHref(historyDepth));
     }
   }
+  nameOverlaysHere();
   syncWaiters.forEach((cb) => cb());
 }
 
+// The address of the entry `depth` overlays up: the keys of those overlays, none of the others'.
+// Undefined (the address as it is) while no overlay names any.
+function overlayHref(depth: number): string | undefined {
+  if (overlayUrlKeys.size === 0) return undefined;
+  const updates: OverlayUrl = {};
+  for (const k of overlayUrlKeys) updates[k] = null;
+  for (const o of overlayStack.slice(0, depth)) Object.assign(updates, o.url);
+  return urlWithParams(updates);
+}
+
+// Write the current entry's overlay keys, once the history has caught up with the stack (before
+// that, the current entry may be one about to be pushed over or stepped back from).
+function nameOverlaysHere(): void {
+  if (historyDepth !== overlayStack.length || pendingProgrammatic > 0) return;
+  const href = overlayHref(historyDepth);
+  if (href != null && href !== hrefNow())
+    window.history.replaceState(window.history.state, "", href);
+}
+
+const hrefNow = () => window.location.pathname + window.location.search + window.location.hash;
+
 function scheduleReconcile(): void {
   if (reconcileScheduled) return;
   reconcileScheduled = true;
@@ -328,6 +363,7 @@ function ensureOverlayListener(): void {
       pendingProgrammatic--; // our own back(): consume and ignore
       // The last one landed: an overlay that opened while it was in flight still owes its entry.
       if (pendingProgrammatic === 0 && historyDepth < overlayStack.length) scheduleReconcile();
+      else nameOverlaysHere();
       return;
     }
     // Genuine user Back: the browser already dropped one overlay entry, so close the topmost
@@ -449,15 +485,21 @@ export function closeTopOverlayThenRun(close: () => void, run: () => void): void
 }
 
 /** While the calling component is mounted, Back (or the browser/mouse back button) closes it via
- * `onClose` instead of navigating away. Mount the component only while the overlay is open. */
-export function useBackToClose(onClose: () => void): void {
+ * `onClose` instead of navigating away. Mount the component only while the overlay is open.
+ * `url`: what the overlay names in its entry's address (a null value: the key absent), followed as
+ * it changes; the entry under it never carries those keys. */
+export function useBackToClose(onClose: () => void, url?: OverlayUrl): void {
   const cb = useEffectEvent(onClose);
+  const named = useEffectEvent(() => url);
+  const entryRef = useRef<Overlay | null>(null);
   useEffect(() => {
     ensureOverlayListener();
     const entry: Overlay = { token: nextOverlayToken(), cb: () => cb() };
+    entryRef.current = entry;
     overlayStack.push(entry);
     scheduleReconcile();
     return () => {
+      entryRef.current = null;
       const idx = overlayStack.indexOf(entry);
       // idx === -1 means the shared handler already removed us on a real user Back; either way,
       // just re-sync history to the (possibly unchanged) overlay count on the next tick.
@@ -465,6 +507,16 @@ export function useBackToClose(onClose: () => void): void {
       scheduleReconcile();
     };
   }, []);
+  // After the effect above (declaration order), so the first run names the entry before it is pushed.
+  const urlDep = url ? JSON.stringify(url) : "";
+  useEffect(() => {
+    const entry = entryRef.current;
+    const next = named();
+    if (!entry || !next) return;
+    entry.url = next;
+    for (const k of Object.keys(next)) overlayUrlKeys.add(k);
+    nameOverlaysHere();
+  }, [urlDep]);
 }
 
 /** A Back-closable layer that exists only WHILE `active`. Stacks on top of `useBackToClose` and any

frontend/src/lib/moduleDef.ts

@@ -50,4 +50,8 @@ export type ModuleDef = {
   // along onto another's URL. Empty for a page with nothing of its own in the URL. Each key belongs to
   // one module and none is a shell key (moduleUrl.contract.test).
   urlKeys: readonly string[];
+  // Its page plays YouTube videos in the player and reopens it from an address that names one (a
+  // reload, a bookmark — lib/playerUrlState), with its own list as the queue. A page without it gets
+  // the shell's player for such an address: the video alone.
+  playsVideos?: boolean;
 };

frontend/src/lib/playerUrlState.ts

@@ -0,0 +1,42 @@
+// The YouTube player's address-bar keys. The player opens over any page (the feed, a channel page, Home,
+// a playlist, a channel's watched videos), so its keys are the shell's: no module owns them, a page
+// switch clears them, and the page under it keeps its own. The player names them in its own history
+// entry (lib/history's `useBackToClose`), so Back lands on the page as it was, without the player.
+// The list it plays from is the page's: the feed's filters, the open playlist (`pl`) — already named.
+// No position: the player resumes from the server's (`video_states`), which is where it was left.
+export const PLAYER_WATCH_KEY = "watch"; // the item of the list playing now
+export const PLAYER_RELATED_KEY = "wrel"; // a related video played in place over it
+export const PLAYER_PANEL_KEY = "wtab"; // the wide panel's tab, when it is not the description
+export const PLAYER_KEYS = [PLAYER_WATCH_KEY, PLAYER_RELATED_KEY, PLAYER_PANEL_KEY] as const;
+
+export type PlayerPanelTab = "description" | "related";
+
+export type PlayerUrlState = { watch: string; related: string | null; panel: PlayerPanelTab };
+
+/** The player's keys for its entry. The panel's tab is written only when it is not the default: no
+ *  browser remembers it, so a link without one opens the description as this one would. */
+export function playerParamUpdates(state: PlayerUrlState): Record<string, string | null> {
+  return {
+    [PLAYER_WATCH_KEY]: state.watch,
+    [PLAYER_RELATED_KEY]: state.related,
+    [PLAYER_PANEL_KEY]: state.panel === "related" ? "related" : null,
+  };
+}
+
+/** The player an address names, or null when it names none. */
+export function playerFrom(params: URLSearchParams): PlayerUrlState | null {
+  const watch = params.get(PLAYER_WATCH_KEY);
+  if (!watch) return null;
+  return {
+    watch,
+    related: params.get(PLAYER_RELATED_KEY) || null,
+    panel: params.get(PLAYER_PANEL_KEY) === "related" ? "related" : "description",
+  };
+}
+
+/** The player the address names now: read by a host as it mounts (a reload, a bookmark), and by the
+ *  player as it opens. No entry but the player's own carries these keys once the history has caught
+ *  up, so a host mounted later (a page switch back) finds none. */
+export function linkedPlayer(): PlayerUrlState | null {
+  return playerFrom(new URLSearchParams(window.location.search));
+}

frontend/src/lib/plexUrlState.dom.test.ts

@@ -48,15 +48,26 @@ const BASE: PlexUrlState = {
 };
 
 describe("plexParamUpdates", () => {
-  it("emits nothing for the all-default state", () => {
+  it("writes the default view in full: this account remembers one a link must not inherit", () => {
     expect(plexParamUpdates(BASE)).toEqual({
-      pscope: null,
-      psort: null,
-      pshow: null,
-      pf: null,
+      pscope: "both",
+      psort: "title:asc",
+      pshow: "all",
+      pf: "",
     });
   });
 
+  it("a link to the default view opens it over another remembered one", () => {
+    const params = applyUpdates(plexParamUpdates(BASE));
+    const back = plexParamsToState(params, {
+      scope: "movie",
+      sort: { key: "year", dir: "desc" },
+      show: "watched",
+      filters: RICH_FILTERS,
+    });
+    expect(back).toEqual(BASE);
+  });
+
   it("clears every key when passed null (off-plex page)", () => {
     expect(plexParamUpdates(null)).toEqual({
       pscope: null,
@@ -66,7 +77,7 @@ describe("plexParamUpdates", () => {
     });
   });
 
-  it("emits only non-default keys", () => {
+  it("writes the view picked", () => {
     const u = plexParamUpdates({
       scope: "movie",
       sort: { key: "year", dir: "desc" },
@@ -76,7 +87,7 @@ describe("plexParamUpdates", () => {
     expect(u.pscope).toBe("movie");
     expect(u.psort).toBe("year:desc");
     expect(u.pshow).toBe("in_progress");
-    expect(u.pf).toBeNull();
+    expect(u.pf).toBe("");
   });
 });
 

frontend/src/lib/plexUrlState.ts

@@ -3,11 +3,11 @@
 // urlState. Keys are NAMESPACED (`pscope`/`psort`/`pshow`/`pf`) rather than reusing the feed's bare
 // `scope`/`sort`/`show`: FeedFiltersProvider actively STRIPS its own KEYS from the URL whenever the app
 // is off the feed page, so a shared key would be deleted out from under the Plex page. The namespaced
-// keys are Plex-unique (like `?v=`/`?pl`), so no other provider ever reads or clears them. Only non-
-// default values are emitted, so URLs stay clean.
+// keys are Plex-unique (like `?v=`/`?pl`), so no other provider ever reads or clears them. Every key is
+// written on the page, its default too: a page opened without one takes this account's remembered view,
+// which may not be the one bookmarked.
 import { parsePlexFilters, plexFiltersToParams, type PlexFilters } from "./api";
-import { decodeSortParam, encodeSortParam, type SortState } from "./columnSort";
-import { PLEX_SORT_FALLBACK } from "./plexSort";
+import { decodeSortParamOrNone, encodeSortParamOrNone, type SortState } from "./columnSort";
 import { parsePlexField, type PlexSearchField } from "./plexSearch";
 
 // The content state this mirrors. `sort` is the RAW provider SortState (scope-healed only at the point of
@@ -30,25 +30,18 @@ export const PLEX_SUB_KEY = "v";
 const SCOPES = ["movie", "show", "both"];
 const SHOWS = ["all", "unwatched", "in_progress", "watched"];
 
-// Sort ⇄ `key:dir` (e.g. `year:desc`) via the shared codec in columnSort; the Plex default (`title:asc`)
-// emits nothing.
-function encodeSort(s: SortState): string | null {
-  if (!s || (s.key === PLEX_SORT_FALLBACK?.key && s.dir === PLEX_SORT_FALLBACK?.dir)) return null;
-  return encodeSortParam(s);
-}
-
-/** The address-bar delta for the Plex content state: each namespaced key mapped to its emitted value,
- * or null to delete it (so a control back at its default clears the key). Pass `null` to clear ALL Plex
+/** The address-bar delta for the Plex content state: each namespaced key mapped to its value (sort as
+ * `key:dir`, the shared columnSort codec; an empty filter set as `pf=`). Pass `null` to clear ALL Plex
  * keys — used when the app is off the Plex page (localStorage still holds the state; it re-mirrors on
  * return). Feed the result into urlWithParams(). */
 export function plexParamUpdates(state: PlexUrlState | null): Record<string, string | null> {
   if (!state) return { pscope: null, psort: null, pshow: null, pf: null };
   const pf = plexFiltersToParams(state.filters).toString();
   return {
-    pscope: state.scope && state.scope !== "both" ? state.scope : null,
-    psort: encodeSort(state.sort),
-    pshow: state.show && state.show !== "all" ? state.show : null,
-    pf: pf || null,
+    pscope: state.scope || "both",
+    psort: encodeSortParamOrNone(state.sort),
+    pshow: state.show || "all",
+    pf,
   };
 }
 
@@ -62,8 +55,8 @@ export function hasPlexParams(params: URLSearchParams): boolean {
 export function plexParamsToState(params: URLSearchParams, base: PlexUrlState): PlexUrlState {
   const scope = params.get("pscope");
   const show = params.get("pshow");
-  const psort = params.get("psort");
-  const sort = psort != null ? (decodeSortParam(psort) ?? base.sort) : base.sort;
+  const linkedSort = decodeSortParamOrNone(params.get("psort"));
+  const sort = linkedSort === undefined ? base.sort : linkedSort;
   return {
     scope: scope && SCOPES.includes(scope) ? scope : base.scope,
     sort,

frontend/src/lib/queryKeys.test.ts

@@ -33,6 +33,7 @@ describe("qk — single-id and scalar keys", () => {
   it("returns [root, id]", () => {
     expect(qk.channel("c1")).toEqual(["channel", "c1"]);
     expect(qk.videoDetail("v1")).toEqual(["video-detail", "v1"]);
+    expect(qk.videoRow("v1")).toEqual(["video-row", "v1"]);
     expect(qk.playlistMembership("v1")).toEqual(["playlist-membership", "v1"]);
     expect(qk.plexItem("i1")).toEqual(["plex-item", "i1"]);
     expect(qk.plexPlaylist(9)).toEqual(["plex-playlist", 9]);

frontend/src/lib/queryKeys.ts

@@ -32,6 +32,7 @@ export const qk = {
   ytSearch: (q?: string | null, count?: number) =>
     q !== undefined ? (["yt-search", q, count] as const) : (["yt-search"] as const),
   videoDetail: (id: string) => ["video-detail", id] as const,
+  videoRow: (id: string) => ["video-row", id] as const,
   related: (id?: string, region?: string) =>
     id !== undefined ? (["related", id, region] as const) : (["related"] as const),
   // This session's confirmed marks per video (lib/progressCache `markVideo`): no fetch behind it.

frontend/src/lib/urlState.ts

@@ -6,6 +6,7 @@
 // the short module/channel name (NavigationProvider owns document.title) — the query never leaks into it.
 import { TAG_CATEGORIES, type FeedFilters } from "./api";
 import { CHANNEL_PAGE_KEYS } from "./channelPageUrlState";
+import { PLAYER_KEYS } from "./playerUrlState";
 
 export const FEED_KEYS = [
   "q",
@@ -33,12 +34,14 @@ export const FEED_KEYS = [
 const KEYS = FEED_KEYS;
 
 // The keys the shell itself reads, whatever page is on screen: the page, the channel page and its view
-// (it opens over any page, lib/channelPageUrlState), the welcome card's mode and the one-time entry links. No module may declare one of
-// these (moduleUrl.contract.test), and a page switch never clears them.
+// (it opens over any page, lib/channelPageUrlState), the YouTube player (the same, lib/playerUrlState),
+// the welcome card's mode and the one-time entry links. No module may declare one of these
+// (moduleUrl.contract.test); a page switch clears only the channel's and the player's.
 export const SHELL_KEYS = [
   "page",
   "chan",
   ...CHANNEL_PAGE_KEYS,
+  ...PLAYER_KEYS,
   "m",
   "link",
   "oauth",
@@ -231,12 +234,13 @@ export function urlWithParams(updates: Record<string, string | null>): string {
 }
 
 /** The channel page's address, opened over the page on screen: the shell's own keys (the page, an
- * entry link not yet read) and the channel — none of the page's keys, and none of another channel's
- * view (the channel page writes its own, lib/channelPageUrlState). What `openChannel` pushes, and what a
+ * entry link not yet read) and the channel — none of the page's keys, none of another channel's view
+ * (the channel page writes its own, lib/channelPageUrlState), and no player (opening a channel closes
+ * it). What `openChannel` pushes, and what a
  * channel link points at, so a new tab opens the same view. */
 export function channelUrl(id: string): string {
   const here = new URLSearchParams(window.location.search);
-  const viewKeys: readonly string[] = CHANNEL_PAGE_KEYS;
+  const viewKeys: readonly string[] = [...CHANNEL_PAGE_KEYS, ...PLAYER_KEYS];
   const params = new URLSearchParams();
   for (const k of SHELL_KEYS) {
     const v = k === "chan" ? id : here.get(k);

frontend/src/moduleUrl.contract.test.ts

@@ -16,6 +16,7 @@ import { plexParamUpdates, plexSearchParamUpdates } from "./lib/plexUrlState";
 import { activityParamUpdates, DEFAULT_ACTIVITY_STATE } from "./lib/activityUrlState";
 import { DEFAULT_LOGS_STATE, logsParamUpdates } from "./lib/logsUrlState";
 import { FILES_KEYS } from "./lib/filesUrlState";
+import { PLAYER_KEYS, playerParamUpdates } from "./lib/playerUrlState";
 import { playlistViewParamUpdates } from "./lib/playlistsUrlState";
 import { SETTINGS_TAB_KEY } from "./lib/settingsTab";
 import { CONFIG_TAB_KEY } from "./lib/configTab";
@@ -128,6 +129,14 @@ describe("module URL keys", () => {
     );
   });
 
+  // The player opens over any page too, and names itself in its own history entry.
+  it("leave the player's keys to the shell", () => {
+    const shell: readonly string[] = SHELL_KEYS;
+    expect(PLAYER_KEYS.filter((k) => !shell.includes(k))).toEqual([]);
+    const written = playerParamUpdates({ watch: "v1", related: "v2", panel: "related" });
+    expect(Object.keys(written).sort()).toEqual([...PLAYER_KEYS].sort());
+  });
+
   it.each([...REGISTERED_PAGES])("are exactly what %s's encoders write", (page) => {
     const declared = [...moduleDef(page).urlKeys].sort();
     const writes = WRITES[page];

frontend/src/modules/channels/ChannelsProvider.dom.test.tsx

@@ -106,13 +106,13 @@ describe("ChannelsProvider — shareable URL", () => {
     expect(result.current.filters).toEqual({ sync: "needsFull" });
   });
 
-  it("mirrors the tab into the address bar and clears it back to the default", () => {
+  it("mirrors the tab into the address bar, the default one too", () => {
     const { result } = render();
     act(() => result.current.setView("blocked"));
     expect(new URLSearchParams(window.location.search).get("ctab")).toBe("blocked");
-    // Back to the default tab clears the key (only non-defaults are emitted).
+    // The default tab is named as well: a link without it would open the tab this browser remembers.
     act(() => result.current.setView("subscribed"));
-    expect(new URLSearchParams(window.location.search).has("ctab")).toBe(false);
+    expect(new URLSearchParams(window.location.search).get("ctab")).toBe("subscribed");
   });
 
   it("a PARTIAL shared link does not clobber the account's stored sort/filters", () => {

frontend/src/modules/feed/Feed.playerSession.dom.test.tsx

@@ -53,11 +53,13 @@ vi.mock("../../features/player/PlayerModal", async () => {
   return {
     default: function Player({
       video,
+      queue,
       onState,
       onWrite,
       onClose,
     }: {
       video: { id: string };
+      queue?: { id: string }[];
       onState: (id: string, status: string, v?: unknown) => void;
       onWrite?: (write: Promise<unknown>) => void;
       onClose: () => void;
@@ -71,6 +73,9 @@ vi.mock("../../features/player/PlayerModal", async () => {
       );
       return (
         <div>
+          <p>
+            playing {video.id} in {queue ? queue.map((v) => v.id).join(",") : "no list"}
+          </p>
           <button onClick={() => onState(video.id, "watched")}>mark</button>
           <button
             onClick={() =>
@@ -116,6 +121,7 @@ afterEach(() => {
   player.watchOnUnmount = false;
   player.flush = null;
   clearAll();
+  window.history.replaceState(null, "", "/");
 });
 
 // A cached related list (the player's, kept for the session) holding these videos.
@@ -190,6 +196,23 @@ function mount({
   return { qc, feed, summary };
 }
 
+// The URL is the view: a reload or a bookmark of the player reopens it once the list is in.
+describe("Feed — a player the address names", () => {
+  it("reopens on its video, the list as its queue", async () => {
+    window.history.replaceState(null, "", "/?watch=v1");
+    mount();
+    expect(await screen.findByText("playing v1 in v1")).toBeTruthy();
+  });
+
+  it("plays a video the loaded list does not hold alone, from the catalog", async () => {
+    window.history.replaceState(null, "", "/?watch=far");
+    const row = vi.spyOn(api, "videoRow").mockResolvedValue({ ...video("new"), id: "far" });
+    mount();
+    expect(await screen.findByText("playing far in no list")).toBeTruthy();
+    expect(row).toHaveBeenCalledWith("far");
+  });
+});
+
 describe("Feed — a video marked watched in the player", () => {
   it("stays out of an Unwatched view when the player writes its position into the cache", async () => {
     const { qc } = mount();

frontend/src/modules/feed/Feed.tsx

@@ -80,6 +80,8 @@ import ViewSwitcher from "../../components/ui/ViewSwitcher";
 import VirtualFeed from "./VirtualFeed";
 import SegmentedToggle from "../../components/ui/SegmentedToggle";
 import { IconButton } from "../../components/ui/IconButton";
+import { useOpenLinkedPlayer } from "../../features/player/useOpenLinkedPlayer";
+
 // Lazy: the in-app YouTube player (IFrame API) loads only when a video is first opened.
 const PlayerModal = lazy(() => import("../../features/player/PlayerModal"));
 
@@ -209,10 +211,13 @@ export default function Feed({
   // A reset's position 0 lives in the cached lists (see onResetState), where a refetch that set out
   // before the server took the reset puts the old position back: written again on its landing.
   const resets = useRef(new Map<string, number>());
-  // The open player: which video and where to start (null = resume from saved position).
-  const [activeVideo, setActiveVideo] = useState<{ video: Video; startAt: number | null } | null>(
-    null,
-  );
+  // The open player: which video and where to start (null = resume from saved position). `alone`:
+  // opened from an address naming a video this list has not loaded, so it plays without the queue.
+  const [activeVideo, setActiveVideo] = useState<{
+    video: Video;
+    startAt: number | null;
+    alone?: boolean;
+  } | null>(null);
   const qc = useQueryClient();
   const videoMarks = useVideoMarks();
   // Live search turned off on this instance: the empty feed offers no search that would be refused.
@@ -509,6 +514,18 @@ export default function Feed({
   // sequence (no reindex/reload mid-play), matching "watched doesn't affect the list". A video that
   // goes hidden still drops out ("visible affects").
   const playerQueue: Video[] = merged.filter((v) => v.status !== "hidden");
+  // A reload or a bookmark of the player reopens it once this list is in, the list as its queue again
+  // (the feed's filters are in the address under it). Not over a live search: that is not in the
+  // address, and a reload leaves it.
+  useOpenLinkedPlayer(
+    !ytActive && !query.isLoading,
+    (id) => playerQueue.find((v) => v.id === id),
+    (video, inList) => {
+      openVideo(video);
+      // Not in what this list has loaded (further down it, or no longer in it): it plays alone.
+      if (!inList) setActiveVideo((a) => a && { ...a, alone: true });
+    },
+  );
 
   // A live search ingests new catalog videos, so the disabled feed queries still hold their stale
   // pre-search cache. Drop them so the feed re-fetches fresh on return.
@@ -1006,7 +1023,7 @@ export default function Feed({
           <PlayerModal
             video={activeVideo.video}
             startAt={activeVideo.startAt}
-            queue={playerQueue}
+            queue={activeVideo.alone ? undefined : playerQueue}
             onClose={closePlayer}
             onState={onState}
             onWrite={trackSessionWrite}

frontend/src/modules/feed/module.ts

@@ -17,6 +17,7 @@ export const feedModule: ModuleDef = {
   Page: lazyWithPreloadAlongside(() => import("./FeedPage"), Rail),
   Store: FeedStore,
   urlKeys: FEED_KEYS,
+  playsVideos: true,
 };
 
 // The channel page: a feed scoped to one channel, opened over any page (App renders it in place of the

frontend/src/modules/files/FilePreview.tsx

@@ -14,6 +14,7 @@ import { formatBytes } from "../../lib/format";
 import { dispatch, setScopeCoveredProbe, useKeyScope } from "../../lib/keymap";
 import { useLayer } from "../../lib/layerStack";
 import { qk } from "../../lib/queryKeys";
+import { FILES_VIEW_KEY } from "../../lib/filesUrlState";
 import { jobTitle } from "../../features/downloads/downloadTitle";
 import { type ActionMenuItem } from "../../components/ui/ActionMenu";
 import { ContextMenu } from "../../components/ui/ContextMenu";
@@ -128,6 +129,7 @@ export default function FilePreview({
       title={<span className="block truncate">{title}</span>}
       onClose={onClose}
       maxWidth="max-w-6xl"
+      url={{ [FILES_VIEW_KEY]: String(file.id) }}
       headerActions={
         <>
           <IconButton

frontend/src/modules/files/Files.menu.dom.test.tsx

@@ -745,6 +745,51 @@ describe("Files · the viewer", () => {
   });
 });
 
+// The URL is the view: the file open over the list is named in the address, so a reload or a bookmark
+// reopens it once the list is in.
+describe("Files · a file the address names", () => {
+  const doc = (id: number) =>
+    file(id, {
+      job_kind: "upload",
+      display_name: `Doc ${id}`,
+      asset: { media_kind: "file", preview: "pdf", container: "pdf", size_bytes: 10 },
+    } as never);
+  const here = () => new URLSearchParams(window.location.search);
+
+  it("reopens the viewer on it, and the viewer names the file it turns to", async () => {
+    window.history.replaceState(null, "", "/?page=files&fview=2");
+    mocks.files = [doc(2), doc(3)];
+    mocks.folders = [YT];
+    mount();
+    const dialog = await screen.findByRole("dialog");
+    expect(dialog.querySelector("iframe")!.getAttribute("src")).toBe(api.previewUrl(2));
+    await waitFor(() => expect(here().get("fview")).toBe("2"));
+    fireEvent.keyDown(window, { key: "ArrowRight" });
+    await waitFor(() => expect(here().get("fview")).toBe("3"));
+  });
+
+  it("reopens the player on a media file", async () => {
+    window.history.replaceState(null, "", "/?page=files&fplay=1");
+    mocks.files = [file(1)];
+    mocks.folders = [YT];
+    mount();
+    expect(await screen.findByText("playing 1")).toBeTruthy();
+  });
+
+  it("says so when the list no longer holds it", async () => {
+    window.history.replaceState(null, "", "/?page=files&fview=99");
+    mocks.files = [doc(2)];
+    mocks.folders = [YT];
+    mount();
+    await waitFor(() =>
+      expect(mocks.notify).toHaveBeenCalledWith(
+        expect.objectContaining({ level: "warning", message: "files.linkedGone" }),
+      ),
+    );
+    expect(screen.queryByRole("dialog")).toBeNull();
+  });
+});
+
 describe("Files · the view", () => {
   it("starts the list at the scroller's top, so its sticky header does not jump on the first scroll", () => {
     mocks.files = [file(2)];

frontend/src/modules/files/Files.tsx

@@ -10,7 +10,12 @@ import {
   type FileSort,
   type LibraryFile,
 } from "../../lib/api";
-import { type SortState, sortRows } from "../../lib/columnSort";
+import {
+  decodeSortParamOrNone,
+  encodeSortParamOrNone,
+  type SortState,
+  sortRows,
+} from "../../lib/columnSort";
 import { libraryRowActions, sharedRowActions } from "../../lib/downloadActions";
 import { formatBytes, formatDateTime, relativeTime } from "../../lib/format";
 import { focusNavItem } from "../../lib/listNav";
@@ -20,7 +25,7 @@ import { LS, ownKey } from "../../lib/storage";
 import { useCardPager } from "../../lib/useCardPager";
 import { useDebounced } from "../../lib/useDebounced";
 import { useUrlMirror } from "../../lib/useUrlMirror";
-import { decodeFilesSort, encodeFilesSort, FILES_SORT_KEY } from "../../lib/filesUrlState";
+import { FILES_SORT_KEY, openFileFrom } from "../../lib/filesUrlState";
 import { useLiveQuery } from "../../lib/useLiveQuery";
 import { usePref } from "../../lib/usePref";
 import { JobThumb } from "../../features/downloads/downloadRow";
@@ -213,14 +218,14 @@ export default function Files() {
   // A sort the address names wins until one is picked here (which is then the account's again), and
   // the address names the sort on screen.
   const [linkedSort, setLinkedSort] = useState(() =>
-    decodeFilesSort(new URLSearchParams(window.location.search).get(FILES_SORT_KEY)),
+    decodeSortParamOrNone(new URLSearchParams(window.location.search).get(FILES_SORT_KEY)),
   );
   const sort = linkedSort === undefined ? prefSort : linkedSort;
   const setSort = (next: SortState) => {
     setLinkedSort(undefined);
     setPrefSort(next);
   };
-  useUrlMirror({ [FILES_SORT_KEY]: encodeFilesSort(sort) });
+  useUrlMirror({ [FILES_SORT_KEY]: encodeSortParamOrNone(sort) });
   const params = listParams(shown);
   // Live at rest: a download finishing elsewhere (the queue, a clip, another tab) lands here on its own.
   const filesQ = useLiveQuery(qk.files(params), () => api.files(params), { intervalMs: 15000 });
@@ -273,6 +278,23 @@ export default function Files() {
   const play = (file: LibraryFile, fromStart = false) => setPlaying({ file, fromStart });
   // The file open in the viewer (one that is not media), by id: the list under it keeps re-reading.
   const [viewing, setViewing] = useState<number | null>(null);
+  // A reload or a bookmark reopens the file the address names — in the viewer or the player — once
+  // the list it is in has come (its folder, search and sort are in the address too). Once; a file the
+  // list no longer holds is said.
+  const [linkedFile] = useState(() => openFileFrom(new URLSearchParams(window.location.search)));
+  const linkedDone = useRef(linkedFile == null);
+  const listIn = wide ? wideIn && wideQ.data !== undefined : filesQ.data !== undefined;
+  const linkedRow = linkedFile && listIn ? rows.find((f) => f.id === linkedFile.id) : undefined;
+  const openLinked = useEffectEvent((file: LibraryFile | undefined) => {
+    if (!file) notify({ level: "warning", message: t("files.linkedGone") });
+    else if (linkedFile?.open === "play") play(file);
+    else setViewing(file.id);
+  });
+  useEffect(() => {
+    if (linkedDone.current || !listIn) return;
+    linkedDone.current = true;
+    openLinked(linkedRow);
+  }, [listIn, linkedRow]);
 
   const actions = useFileActions({
     folders: foldersQ.data ?? null,

frontend/src/modules/files/LibraryPlayer.tsx

@@ -4,6 +4,7 @@ import { useQueryClient } from "@tanstack/react-query";
 import Modal from "../../components/ui/Modal";
 import { api, type DownloadJob } from "../../lib/api";
 import { qk } from "../../lib/queryKeys";
+import { FILES_PLAY_KEY } from "../../lib/filesUrlState";
 import { jobTitle } from "../../features/downloads/downloadTitle";
 import { exposeVideoToBackgroundPlay } from "../../lib/browserBackgroundPlay";
 import { useMediaLogRef } from "../../lib/mediaLog";
@@ -91,7 +92,13 @@ export default function LibraryPlayer({
   useResume(media, String(job.id), fromStart ? 0 : (job.position_seconds ?? 0), keepPoint);
 
   return (
-    <Modal initialFocus="player" title={title} onClose={onClose} maxWidth="max-w-4xl">
+    <Modal
+      initialFocus="player"
+      title={title}
+      onClose={onClose}
+      maxWidth="max-w-4xl"
+      url={{ [FILES_PLAY_KEY]: String(job.id) }}
+    >
       {isAudio ? (
         <div className="flex flex-col items-center gap-4 py-2">
           {poster ? (

frontend/src/modules/home/Home.dom.test.tsx

@@ -45,9 +45,11 @@ vi.mock("react-i18next", async (importOriginal) => {
 
 const discover = vi.fn();
 const discoverPick = vi.fn();
+const videoRow = vi.fn();
 vi.mock("../../lib/api", () => ({
   api: {
     discover: (...a: unknown[]) => discover(...a),
+    videoRow: (...a: unknown[]) => videoRow(...a),
     discoverPick: (...a: unknown[]) => discoverPick(...a),
     setState: () => Promise.resolve(),
     watchLaterAdd: () => Promise.resolve(),
@@ -70,6 +72,11 @@ vi.mock("../plex/plexContext", () => ({
   usePlexActions: () => ({ setJumpTo: (t: unknown) => setJumpTo(t) }),
 }));
 
+// The player itself is pinned in its own tests: here, what Home opens it on.
+vi.mock("../../features/player/PlayerModal", () => ({
+  default: ({ video }: { video: { id: string } }) => <p>playing {video.id}</p>,
+}));
+
 import Home from "./Home";
 import { requestSurprise, takeSurprise } from "../../lib/homeIntent";
 
@@ -179,6 +186,17 @@ beforeEach(() => {
 });
 afterEach(cleanup);
 
+describe("Home — a player the address names", () => {
+  it("reopens on its video, alone as Home plays it", async () => {
+    window.history.replaceState(null, "", "/?page=home&watch=v9");
+    videoRow.mockResolvedValue({ id: "v9", title: "Nine" });
+    mount();
+    expect(await screen.findByText("playing v9")).toBeTruthy();
+    expect(videoRow).toHaveBeenCalledWith("v9");
+    window.history.replaceState(null, "", "/");
+  });
+});
+
 describe("Home", () => {
   it("labels the hero from the server's tier, not from the card", async () => {
     // The same card shape is served under a `surprise` tier: a client that inferred "where you left

frontend/src/modules/home/Home.tsx

@@ -78,6 +78,7 @@ import {
   mediaTitleClass,
 } from "../../components/ui/mediaCardStyles";
 import RemoteImage from "../../components/ui/RemoteImage";
+import { useOpenLinkedPlayer } from "../../features/player/useOpenLinkedPlayer";
 
 // The Home surface — "Mit nézzek most?".
 //
@@ -729,6 +730,12 @@ export default function Home() {
     window.history.replaceState({ ...window.history.state, [SAVED_KEY]: question }, "");
   }, [budget, seed, press, seen]);
   const [player, setPlayer] = useState<{ video: Video; startAt: number | null } | null>(null);
+  // A reload or a bookmark of the player reopens it: the video alone, as Home plays it.
+  useOpenLinkedPlayer(
+    true,
+    () => undefined,
+    (video) => setPlayer({ video, startAt: null }),
+  );
 
   // A Plex card's title is in the reader's language, so the answer is cached per language.
   const lang = plexLang(i18n.language);

frontend/src/modules/home/module.ts

@@ -14,4 +14,5 @@ export const homeModule: ModuleDef = {
   // Nothing of its own: the question is an answer, not a setting — the same question draws other
   // cards once what you have watched moves on.
   urlKeys: [],
+  playsVideos: true,
 };

frontend/src/modules/playlists/Playlists.dom.test.tsx

@@ -18,6 +18,8 @@ const h = vi.hoisted(() => ({
   mounts: 0,
   player: null as null | {
     video: { id: string; position_seconds: number };
+    queue?: { id: string }[];
+    startIndex?: number;
     onClose: () => void;
     onState: (id: string, status: string) => void;
     onRemoveFromList?: (v: unknown) => Promise<boolean>;
@@ -187,6 +189,27 @@ afterEach(() => {
   window.history.replaceState(null, "", "/");
 });
 
+// The URL is the view: a reload or a bookmark of the player reopens it once the playlist is in.
+describe("Playlists — a player the address names", () => {
+  it("reopens on its video, the playlist's view as the queue", async () => {
+    window.history.replaceState(null, "", "/?page=playlists&pl=1&watch=B");
+    mount({ 1: [vid("A", 0), vid("B", 0)] });
+    await waitFor(() => expect(h.player?.video.id).toBe("B"));
+    expect(h.player!.queue?.map((v) => v.id)).toEqual(["A", "B"]);
+    expect(h.player!.startIndex).toBe(1);
+    expect(h.player!.onRemoveFromList).toBeDefined();
+  });
+
+  it("plays a video the view does not show alone, with nothing to remove it from", async () => {
+    window.history.replaceState(null, "", "/?page=playlists&pl=1&watch=Z");
+    vi.spyOn(api, "videoRow").mockResolvedValue(vid("Z", 0));
+    mount({ 1: [vid("A", 0)] });
+    await waitFor(() => expect(h.player?.video.id).toBe("Z"));
+    expect(h.player!.queue?.map((v) => v.id)).toEqual(["Z"]);
+    expect(h.player!.onRemoveFromList).toBeUndefined();
+  });
+});
+
 describe("Playlists — the row the player is launched with", () => {
   it("carries the position the player just stored, not the one the list first loaded with", async () => {
     // The page renders from its own undoable copy of the list, re-seeded only when the SET of ids

frontend/src/modules/playlists/Playlists.tsx

@@ -50,6 +50,7 @@ import {
 } from "../../lib/playlistsUrlState";
 import { formatRuntime } from "../../lib/format";
 import { applyView, sameOrder } from "../../lib/playlistView";
+import { useOpenLinkedPlayer } from "../../features/player/useOpenLinkedPlayer";
 const PlayerModal = lazy(() => import("../../features/player/PlayerModal"));
 import { Button } from "../../components/ui/Button";
 import { LoadingState, StateMessage } from "../../components/ui/QueryState";
@@ -580,6 +581,17 @@ function PlaylistDetail() {
     shownRef.current = shown;
     removeRef.current = removeItem;
   });
+  // A reload or a bookmark of the player reopens it once this playlist is in, its view as the queue
+  // again (the playlist and its view are in the address under it). A video the view does not show
+  // (filtered out, gone from the list) plays alone, and nothing removes it from a list.
+  useOpenLinkedPlayer(
+    detail != null && items.length > 0,
+    (id) => shown.find((v) => v.id === id),
+    (video, inList) => {
+      if (inList) openPlayer(video.id);
+      else setPlaying({ video, queue: [video], index: 0, listId: selectedId, editable: false });
+    },
+  );
 
   async function moveItemTo(video: Video, target: Playlist) {
     if (selectedId == null) return;

frontend/src/modules/playlists/module.ts

@@ -19,4 +19,5 @@ export const playlistsModule: ModuleDef = {
   Store: PlaylistsProvider,
   // The playlist shown (PlaylistsProvider, playlistsInit).
   urlKeys: PLAYLISTS_KEYS,
+  playsVideos: true,
 };

frontend/src/shell/App.tsx

@@ -29,6 +29,7 @@ import KeyboardHelp from "../components/ui/KeyboardHelp";
 import AppCommandPalette from "./AppCommandPalette";
 import DownloadIntake from "../features/downloads/DownloadIntake";
 import DownloadTray from "../features/downloads/DownloadTray";
+import { LinkedPlayer } from "../features/player/LinkedPlayer";
 import ErrorDialog from "./ErrorDialog";
 import VersionBanner from "./VersionBanner";
 import VerifyBanner from "./VerifyBanner";
@@ -187,6 +188,9 @@ export default function App() {
       <AppCommandPalette />
       {/* The one download dialog: the Files link box, a link pasted onto any page, the palette. */}
       <DownloadIntake />
+      {/* The player an address names over a page that plays none itself (a channel page plays its own,
+          through its feed); decided once, at boot. */}
+      <LinkedPlayer hosted={!!channelView || !!moduleDef(page).playsVideos} />
       {/* The debug recorder: its start dialog, and its pill docked under the toasts. */}
       {me && <DebugRecorder />}
       <Suspense fallback={null}>