fix(files): review round 3, the page — a search waits for the server, the viewer keeps its file, a drop ends the drag

- past the list's cap a search waits in a skeleton, never showing the newest files' 'no match' for a
  file the server is about to find; a sort keeps its stand-in rows
- the viewer keeps the file it was opened on when a server answer replaces the rows under it
- a drop another zone took still clears the page's drop overlay
- 'The first N items' only for a server sort; the past-the-end notice no longer claims the file exists
- a failed server search is tested to say so

frontend/src/components/Files.menu.dom.test.tsx

@@ -38,6 +38,8 @@ const mocks = vi.hoisted(() => ({
   searched: [] as unknown[],
   // The server's search/sort answer is still on its way (no data yet).
   wideLoading: false,
+  // The server's search/sort answer failed.
+  wideFailed: false,
   foldersFailed: false,
   notify: vi.fn(),
 }));
@@ -73,6 +75,14 @@ vi.mock("../lib/useLiveQuery", () => ({
     if (opts?.enabled === false) return { data: undefined, isError: false, isLoading: false };
     mocks.keys.push(key);
     const asked = key[1] as { q?: string; sort?: string } | undefined;
+    if (key[0] === "files" && (asked?.q || asked?.sort) && mocks.wideFailed)
+      return {
+        data: undefined,
+        isError: true,
+        isLoading: false,
+        isFetching: false,
+        refetch: vi.fn(),
+      };
     if (key[0] === "files" && (asked?.q || asked?.sort) && mocks.wideLoading)
       return {
         data: undefined,
@@ -154,6 +164,7 @@ afterEach(() => {
   mocks.fetching = false;
   mocks.titleArgs = [];
   mocks.wideLoading = false;
+  mocks.wideFailed = false;
   mocks.notify.mockClear();
   resetQueueWatch();
 });
@@ -476,11 +487,55 @@ describe("Files · a library past the list's cap", () => {
     expect(screen.getByText("files.countFirst")).toBeTruthy();
     cleanup();
 
+    // A search with no sort of the server's: it answers the newest matches first.
+    mount(ALL_FILES, vi.fn(), "clip");
+    expect(screen.getByText("files.countNewest")).toBeTruthy();
+    cleanup();
+
     mocks.searched = [file(9999, { display_name: "Régi recept" })];
     mount(ALL_FILES, vi.fn(), "recept");
     expect(screen.getByText("files.count")).toBeTruthy();
   });
 
+  it("a search past the cap waits for the server's answer — never a 'no match' it has not given", () => {
+    mocks.folders = [YT];
+    mocks.files = capped();
+    mocks.wideLoading = true;
+    mount(ALL_FILES, vi.fn(), "recept");
+    expect(screen.getByRole("status")).toBeTruthy();
+    expect(screen.queryByText("files.empty.search")).toBeNull();
+  });
+
+  it("a server search that failed says so, not the newest files searched here", () => {
+    mocks.folders = [YT];
+    mocks.files = capped();
+    mocks.wideFailed = true;
+    mount(ALL_FILES, vi.fn(), "clip");
+    expect(screen.getByText("common.loadError")).toBeTruthy();
+    expect(screen.queryByText("Clip 1")).toBeNull();
+  });
+
+  it("a file opened while the server's sort was on its way stays open when the answer leaves it out", async () => {
+    mocks.folders = [YT];
+    const doc = file(7, {
+      job_kind: "upload",
+      display_name: "Doc 7",
+      asset: { media_kind: "file", preview: "pdf", container: "pdf", size_bytes: 10 },
+    } as never);
+    mocks.files = [doc, ...capped().slice(1)];
+    mocks.wideLoading = true;
+    mount();
+    fireEvent.click(nameHeader());
+    fireEvent.click(screen.getByText("Doc 7"));
+    expect(await screen.findByRole("dialog")).toBeTruthy();
+    // The answer: the first files by name, without it.
+    mocks.wideLoading = false;
+    mocks.searched = Array.from({ length: FILES_LIST_CAP }, (_, i) => file(i + 1000));
+    fireEvent.click(nameHeader());
+    expect(screen.getByText("Clip 1499")).toBeTruthy(); // by name, from the end
+    expect(screen.getByRole("dialog")).toBeTruthy();
+  });
+
   it("an arrival waits for the server's answer: the table can only turn to a file it holds", async () => {
     mocks.folders = [YT];
     mocks.files = capped();
@@ -1013,6 +1068,24 @@ describe("Files · dropping a file on the page", () => {
     expect(drag("drop", [new File(["y"], "masik.pdf")]).defaultPrevented).toBe(true);
   });
 
+  it("a drop another zone took still ends the page's drag", () => {
+    mocks.files = [];
+    mocks.folders = [YT, OWN];
+    mount({ kind: "folder", id: 2 });
+    drag("dragenter");
+    expect(screen.getByText("files.drop.here:Cimboráknak")).toBeTruthy();
+    // Taken by a zone over the page (the issue composer's screenshot box): no dragleave follows.
+    const e = new Event("drop", { bubbles: true, cancelable: true });
+    Object.defineProperty(e, "dataTransfer", {
+      value: { types: ["Files"], files: Object.assign([], { item: () => null }) },
+    });
+    e.preventDefault();
+    act(() => {
+      window.dispatchEvent(e);
+    });
+    expect(screen.queryByText("files.drop.here:Cimboráknak")).toBeNull();
+  });
+
   it("the open Upload dialog's own zone keeps the drop it accepted", async () => {
     mocks.files = [];
     mocks.folders = [YT, OWN];