fix(nav): the address follows the view through overlays, reloads and Back (review round 1)

- A URL mirror names the view again on every entry Back or Forward lands on, so a change made
  under a dialog, a drawer or a sub-view is not undone by the next reload.
- A view pushed from the entry a reload under a dialog started from no longer inherits its overlay
  mark; a reload under two overlays closes onto the page in one step.
- The linked player reopens over a live search, gives itself up when its list moves first, and
  plays alone over an emptied playlist; a capped Files list keeps the link it cannot resolve.
- The Feed press over a channel ends the search; leaving a search ends its asked mark; Files and
  Playlists searches end with their page; the feed always names its view and debounces its search.
- Search-box keys are declared per module and kept out of the client log below TRACE.
- Writers outside lib/ go through codecs; the URL contract scans computed keys, overlay writers and
  two-line reads, and holds every page to a bookmark round trip (Config, Activity, Playlists and the
  Files sort and viewer added).

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

@@ -809,6 +809,26 @@ describe("Files · a file the address names", () => {
     // Said once: the address no longer names it, so a reload or a copied link does not say it again.
     expect(here().has("fview")).toBe(false);
   });
+
+  // A list the cap cut cannot tell a deleted file from one beyond its end: it says the file is not
+  // among the ones listed, and keeps the link.
+  it("past the cap with no search or sort to widen it, says it is not listed and keeps the link", async () => {
+    // The case before closed a viewer: its step back lands a moment later, on whatever is current.
+    await new Promise((r) => setTimeout(r, 30));
+    window.history.replaceState(null, "", "/?page=files&fsort=none&fview=9999");
+    mocks.files = Array.from({ length: FILES_LIST_CAP }, (_, i) => file(i + 1));
+    mocks.folders = [YT];
+    mount();
+    await waitFor(() =>
+      expect(mocks.notify).toHaveBeenCalledWith(
+        expect.objectContaining({ level: "info", message: "files.arrival.notListed" }),
+      ),
+    );
+    expect(mocks.notify).not.toHaveBeenCalledWith(
+      expect.objectContaining({ message: "files.linkedGone" }),
+    );
+    expect(here().get("fview")).toBe("9999");
+  }, 30_000); // a full page of FILES_LIST_CAP rows
 });
 
 describe("Files · the view", () => {