fix(nav): the dead-page rewrite does not restore a spent focus stamp

It spread the event's snapshot, which still carried the sfNav stamp lib/history's own listener had
just taken off the entry, so a later landing there (an overlay closing) refocused a stale item. It
now spreads the live entry (test red on the snapshot). Also: format.test's comment named a test
image that never runs vitest; it is the gate host's locale.

frontend/src/components/NavigationProvider.dom.test.tsx

@@ -191,6 +191,19 @@ describe("NavigationProvider · Back", () => {
     expect(window.history.state).toMatchObject({ sfPage: "feed" });
     expect(window.location.search).toBe("?keep=1");
   });
+
+  // lib/history's own listener takes a spent focus stamp off the entry it lands on; the rewrite must
+  // not put it back, or the next landing there (an overlay closing) would refocus a stale item.
+  it("does not put back the focus stamp the landing spent", () => {
+    render();
+    const st = { sfPage: "messages", sfNav: { list: 0, lists: 1 } };
+    act(() => {
+      window.history.replaceState(st, "", "/?page=messages");
+      window.dispatchEvent(new PopStateEvent("popstate", { state: st }));
+    });
+    expect(window.history.state).toMatchObject({ sfPage: "feed" });
+    expect(window.history.state).not.toHaveProperty("sfNav");
+  });
 });
 
 describe("NavigationProvider · never under an open overlay", () => {

frontend/src/components/NavigationProvider.tsx

@@ -200,11 +200,16 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
       // An entry can name a page this build no longer has (one pushed before a module was removed,
       // reached by Back after a reload onto the new build); that lands on the feed, not on a crash.
       // The entry is rewritten to say so: left alone, the address bar would keep naming the dead page
-      // and a click on Feed would be a no-op (setPage's same-page guard).
+      // and a click on Feed would be a no-op (setPage's same-page guard). It spreads the LIVE entry,
+      // not `e.state`: lib/history's listener ran first and already took the spent `sfNav` off it.
       const sf: unknown = e.state?.sfPage;
       const p: Page = typeof sf === "string" && isPage(sf) ? sf : "feed";
       if (typeof sf === "string" && sf !== p)
-        window.history.replaceState({ ...e.state, sfPage: p }, "", urlWithParams({ page: null }));
+        window.history.replaceState(
+          { ...window.history.state, sfPage: p },
+          "",
+          urlWithParams({ page: null }),
+        );
       setPageState(p);
       setAccountRaw(PAGE_KEY, p);
       // The YouTube-search sub-view and the channel page ride in history.state, so Back/Forward

frontend/src/lib/format.test.ts

@@ -132,8 +132,8 @@ describe("relativeFromMs", () => {
 // A bare `n.toLocaleString()` groups in the BROWSER's locale, so an English UI in a Hungarian browser
 // printed "1 234 567" (and a Hungarian UI in an English browser "1,234,567"). The case below asserts
 // BOTH languages and that the two differ, rather than comparing against the runtime's own default:
-// the default is whatever locale the machine running the suite has (Hungarian on the dev box, English
+// the default is whatever locale the host running the gate has (Hungarian on the dev box, English or
-// in the test image), so a one-language assertion passes under the old bug on half the machines.
+// C on a Linux host), so a one-language assertion passes under the old bug on half the machines.
 describe("formatNumber", () => {
   afterEach(() => {
     i18nStub.language = "en";