fix(nav): a linked player, file and search survive what the app does by itself (review round 2)

- Playlists: a link over a playlist the account does not hold plays alone; the rail's own
  fallback no longer counts as a pick that gives the player up.
- The linked opener opens or clears nothing once the address names another player, and stops
  looking (and fetching its row) once it settled.
- Files: a list the server's cap cut — the sorted or searched one too — keeps the link, with a
  notice of its own (EN/HU).
- History: an in-place view rewrite (search refine, count, channel to channel, sub-view)
  drops a reloaded entry's overlay marks (replaceView); a landing on a channel opened from a
  search keeps the search; the Feed press on a search opens the plain feed.
- Files/Playlists: an emptied search is written at once.
- Client log: plf/cf (column text filters) are typed keys; the shell has none of its own.
- Contract: writers outside lib/ take a literal or a lib/ function's result; every URL key is
  sorted typed or not; the writer regexes are held by a fixture; sub-views named; the bookmark
  net reads page tags.
- Feed defaults in one constant; one live-search queue helper; Scheduler writes through the
  Activity codec; notRun copy (EN/HU) names Forward and a plain "Search YouTube" button.

frontend/src/features/navigation/NavigationProvider.tsx

@@ -17,6 +17,7 @@ import {
   nextNavId,
   notifyNav,
   rememberNavPosition,
+  replaceView,
 } from "../../lib/history";
 import { foreignUrlKeys, moduleUrlKeys, pageTitleKey, reachablePage } from "./moduleRegistry";
 import { CHANNEL_PAGE_KEYS } from "../../lib/channelPageUrlState";
@@ -86,7 +87,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
   // The live YouTube search: named in the address (`yt`, and `ytn` for its count, lib/ytSearchUrlState)
   // so a reload or a link opens it again; its own history entry, so Back steps player → search → feed.
   // Whether it RUNS by itself is not the address's to say: `ytAsked` is the term this document was
-  // asked to search for (sent from the search box, or "Search YouTube again" pressed), on the entries
+  // asked to search for (sent from the search box, or "Search YouTube" pressed), on the entries
   // it has stayed on since — leaving the search ends it. Anything else — a reload, a link, a Back or
   // a Forward onto a search — runs only when it costs no quota (Feed decides).
   const [ytSearch, setYtSearch] = useState<string | null>(() =>
@@ -136,7 +137,8 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
       closeOverlaysThenNavigate(() => {
         // A channel page overlays the content column, so a nav click must close it even when the
         // underlying page is unchanged (e.g. "Feed" while a channel opened from the feed).
-        if (next === pageRef.current && !channelViewRef.current) {
+        // A live search on it is one too: the press opens the page's root, as over a channel.
+        if (next === pageRef.current && !channelViewRef.current && ytSearchRef.current == null) {
           then?.();
           return;
         }
@@ -161,7 +163,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
         notifyNav();
         then?.();
       }),
-    [pageRef, channelViewRef, endYtSearch],
+    [pageRef, channelViewRef, ytSearchRef, endYtSearch],
   );
 
   // A sub-view (channel / YT search) is an OVERLAY, not a page change. Like setPage it never lands
@@ -174,7 +176,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
       const url = channelUrl(id);
       if (window.history.state?._chan) {
         const st = window.history.state;
-        window.history.replaceState({ ...st, _chan: id, _chanName: name ?? null }, "", url);
+        replaceView({ ...st, _chan: id, _chanName: name ?? null }, url);
       } else {
         const st = rememberNavPosition();
         window.history.pushState({ ...st, _chan: id, _chanName: name ?? null }, "", url);
@@ -193,9 +195,8 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
       // again: the channel's address carried none of it.
       setChannelView(null);
       const { _chan: _id, _chanName: _name, ...st } = window.history.state ?? {};
-      window.history.replaceState(
+      replaceView(
         st,
-        "",
         urlWithParams({
           ...closedChannelParams(),
           ...ytSearchParams(ytSearchRef.current, ytCountRef.current),
@@ -212,11 +213,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
     if (st._yt || ytSearchFrom(here) != null) {
       // Refine the search on screen, in place, at the count it shows (one a link opened too: it
       // is the first entry of this document, so its new `_yt` mark has nothing of ours below it).
-      window.history.replaceState(
-        { ...st, _yt: q },
-        "",
-        urlWithParams(ytSearchParams(q, ytCountFrom(here))),
-      );
+      replaceView({ ...st, _yt: q }, urlWithParams(ytSearchParams(q, ytCountFrom(here))));
     } else {
       // New sub-view entry, at the default count.
       setYtCountState(DEFAULT_YT_COUNT);
@@ -235,9 +232,8 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
   const setYtCount = useCallback(
     (n: number) => {
       setYtCountState(n);
-      window.history.replaceState(
-        window.history.state,
-        "",
+      replaceView(
+        window.history.state ?? {},
         urlWithParams(ytSearchParams(ytSearchRef.current, n)),
       );
     },
@@ -251,7 +247,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
     else {
       endYtSearch();
       const { _yt: _q, ...st } = window.history.state ?? {};
-      window.history.replaceState(st, "", urlWithParams(ytSearchParams(null, DEFAULT_YT_COUNT)));
+      replaceView(st, urlWithParams(ytSearchParams(null, DEFAULT_YT_COUNT)));
     }
   }, [endYtSearch]);
 
@@ -263,10 +259,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
   const [pageSearchWasOn, setPageSearchWasOn] = useState(page);
   if (pageSearchWasOn !== page) {
     setPageSearchWasOn(page);
-    if (page !== "feed") {
-      setYtSearch(null);
-      setYtAsked(null);
-    }
+    if (page !== "feed") endYtSearch();
   }
 
   // The browser tab names the place and the object in it (DESIGN § Composition, "Where am I"):
@@ -349,8 +342,12 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
       // The YouTube search is read from the address the browser restored, so Back/Forward opens or
       // clears it to match the entry we landed on. One landed on without it has ended: a Forward back
       // onto it is not asked for, and an API search waits for a press.
+      // A channel page opened from its results stands over it: its entry carries the search's mark
+      // (its address does not), and the search stays under it — closing a player over that channel
+      // lands there, and is no leaving of the search.
       const here = new URLSearchParams(window.location.search);
-      const landed = p === "feed" ? ytSearchFrom(here) : null;
+      const under = e.state?._chan && typeof e.state._yt === "string" ? e.state._yt : null;
+      const landed = p === "feed" ? (ytSearchFrom(here) ?? under) : null;
       setYtSearch(landed);
       if (landed == null) setYtAsked(null);
       setYtCountState(ytCountFrom(here));