fix(nav): the address keeps what the app rewrites around it (review round 3)

- The Feed press over a live search ends only the search: the feed's own view stays named.
- Leaving a search steps back only off an entry the app pushed (_ytOwn); one a link or a reload
  opened is cleared in place, also where the Navigation API is missing.
- useUrlMirror rewrites a changed view through replaceView, so a reload's overlay marks go; its
  first write and its landing writes keep them for an overlay that reopens.
- Files and Playlists: a box emptied and filled again settles at once, never naming the ended search.
- Playlists: a linked player is scoped to the playlist the store started with, and only the rail's
  own move to the first playlist is no pick.
- Contract: writer objects are scanned to their matching brace, a computed or shorthand key is
  refused, and every useHistorySubview call hands a named definition.
- Lint: playwright/no-skipped-test also refuses fixme (gate snapshot regenerated).
- FEED_DEFAULT_SORT at the three remaining sites; linkedNotListed says to search by name.

frontend/src/features/navigation/NavigationProvider.tsx

@@ -64,6 +64,13 @@ function pageRootParams(page: Page): Record<string, string | null> {
   };
 }
 
+/** The address of the page under a live search, the search ended: no search, player or channel. */
+const searchEndParams = (): Record<string, string | null> => ({
+  ...closedChannelParams(),
+  ...nulls(PLAYER_KEYS),
+  ...ytSearchParams(null, DEFAULT_YT_COUNT),
+});
+
 const nulls = (keys: readonly string[]) => Object.fromEntries(keys.map((k) => [k, null]));
 
 /** No channel page: neither `chan` nor its view's keys, which the page itself writes (ChannelPage) —
@@ -138,7 +145,8 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
         // 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).
         // 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) {
+        const samePage = next === pageRef.current && !channelViewRef.current;
+        if (samePage && ytSearchRef.current == null) {
           then?.();
           return;
         }
@@ -154,11 +162,13 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
         // every module's own keys (pageRootParams) — a page switch resets to that module's root, and
         // each module's store mirrors its state back in on its page. The item it was opened from is
         // still focused: the state setters above have not re-rendered anything yet.
+        // The press on a search over its own page ends only the search: the page's view is the one
+        // on screen and stays named — its store, unchanged, writes nothing back in.
         rememberNavPosition();
         window.history.pushState(
           { sfPage: next, sfScroll: nextNavId() },
           "",
-          urlWithParams(pageRootParams(next)),
+          urlWithParams(samePage ? searchEndParams() : pageRootParams(next)),
         );
         notifyNav();
         then?.();
@@ -215,11 +225,11 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
       // is the first entry of this document, so its new `_yt` mark has nothing of ours below it).
       replaceView({ ...st, _yt: q }, urlWithParams(ytSearchParams(q, ytCountFrom(here))));
     } else {
-      // New sub-view entry, at the default count.
+      // New sub-view entry, at the default count — ours (`_ytOwn`): leaving it steps back off it.
       setYtCountState(DEFAULT_YT_COUNT);
       const left = rememberNavPosition();
       window.history.pushState(
-        { ...left, sfPage: "feed", _yt: q },
+        { ...left, sfPage: "feed", _yt: q, _ytOwn: 1 },
         "",
         urlWithParams(ytSearchParams(q, DEFAULT_YT_COUNT)),
       );
@@ -242,11 +252,13 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
 
   const exitYtSearch = useCallback(() => {
     // Pop our search entry (so Forward still works); fall back to a clear in place if we don't own
-    // one, or there is no entry of this document below it (a full tab, see backStaysInDocument).
-    if (window.history.state?._yt && backStaysInDocument()) window.history.back();
+    // one — a search a link or a reload opened is marked (`_yt`) but was pushed by nobody: below it is
+    // another site, or nothing — or there is no entry of this document below it (a full tab, see
+    // backStaysInDocument).
+    if (window.history.state?._ytOwn && backStaysInDocument()) window.history.back();
     else {
       endYtSearch();
-      const { _yt: _q, ...st } = window.history.state ?? {};
+      const { _yt: _q, _ytOwn: _own, ...st } = window.history.state ?? {};
       replaceView(st, urlWithParams(ytSearchParams(null, DEFAULT_YT_COUNT)));
     }
   }, [endYtSearch]);
@@ -322,7 +334,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
     if (named != null) {
       window.history.replaceState({ ...st, _yt: named, sfPage: mountPage }, "", url);
     } else {
-      const { _yt: _staleYt, _ytScrape: _staleScrape, ...rest } = st;
+      const { _yt: _staleYt, _ytScrape: _staleScrape, _ytOwn: _staleOwn, ...rest } = st;
       window.history.replaceState({ ...rest, sfPage: mountPage }, "", url);
     }
     function onPop(e: PopStateEvent) {

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

@@ -243,6 +243,33 @@ describe("NavigationProvider · the YouTube search in the address", () => {
     expect(window.history.length).toBe(depth + 1); // its own entry: Back returns to the search
   });
 
+  it("the Feed press on the search keeps the feed's own view in the address", () => {
+    window.history.replaceState({ sfPage: "feed" }, "", "/?page=feed&show=all&sort=oldest");
+    const { result } = render();
+    act(() => result.current.enterYtSearch("lofi"));
+    act(() => result.current.setPage("feed"));
+    expect(search().get("yt")).toBeNull();
+    expect([search().get("show"), search().get("sort")]).toEqual(["all", "oldest"]);
+  });
+
+  it("a search sent from the box is left by a step back off its own entry", () => {
+    const { result } = render();
+    act(() => result.current.enterYtSearch("lofi"));
+    const back = vi.spyOn(window.history, "back").mockImplementation(() => {});
+    act(() => result.current.exitYtSearch());
+    expect(back).toHaveBeenCalledTimes(1);
+  });
+
+  it("a search a link opened is left in place, not by a step back off the document", () => {
+    window.history.replaceState(null, "", "/?page=feed&yt=lofi");
+    const { result } = render();
+    const back = vi.spyOn(window.history, "back");
+    act(() => result.current.exitYtSearch());
+    expect(back).not.toHaveBeenCalled();
+    expect(result.current.ytSearch).toBeNull();
+    expect(search().get("yt")).toBeNull();
+  });
+
   it("a landing on a channel opened from the search (an overlay over it closing) keeps the search", () => {
     const { result } = render();
     act(() => result.current.enterYtSearch("lofi"));