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.

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;