fix(files): review round 1, the page — honest states, the keyboard, the tray's words

- A library past the list's cap is searched and sorted on the server; the count says "the newest".
- Each folder and each search opens on its first page (DataTable pageScope, useCardPager scope).
- A file dropped where the page takes none never reaches the browser (which would unload the app).
- The viewer's arrows wait while a layer opened from it is on top, and scroll a wide text line;
  a text shows its first 5000 lines and says where the rest is.
- Confirms name the file (no more "your downloads"); the asking menu rows end in "…".
- The tray names a running step beside its bar, shows a pause mark for paused work, polls slowly
  while only paused work waits, and forgets a finished file that was deleted.
- An unchanged rename sends nothing; a paste opens the download dialog only with nothing on top;
  the link box never replaces what was typed.
- Honest states: folders that failed to load, a file no longer there, the storage figure; the rail
  says "nothing downloaded" only when there is nothing.
- Focus after deleting the open folder and when the format form opens; the format name's label.
- ui/Meter (one danger line for both quota bars) and ui/RenameField in the platform layer.
- Copy fixes, stale comments and the speculative hub key; a contract test for the list's
  parameters; e2e: the Files page and the paste intake.

frontend/src/components/FilePreview.tsx

@@ -12,6 +12,7 @@ import {
 import { api, HttpError, type FilePreviewKind, type LibraryFile } from "../lib/api";
 import { formatBytes } from "../lib/format";
 import { dispatch, useKeyScope } from "../lib/keymap";
+import { useLayer } from "../lib/layerStack";
 import { qk } from "../lib/queryKeys";
 import { jobTitle } from "./downloadTitle";
 import { type ActionMenuItem } from "./ui/ActionMenu";
@@ -32,6 +33,8 @@ import { useContextMenu } from "./ui/useContextMenu";
 //
 // Every kind fills the same stage, so a step never resizes the dialog: its ‹ › stay under the pointer.
 const STAGE = "h-[min(75dvh,56rem)] w-full";
+// How many lines of a text file the viewer lays out (see TextStage).
+const TEXT_LINES = 5000;
 
 /** A text file's head (one read, shared by the viewer's header and its stage). */
 function useTextPreview(id: number, enabled: boolean) {
@@ -74,7 +77,17 @@ export default function FilePreview({
     if (next) onFileChange(next.id);
   };
   useKeyScope("fileViewer");
+  // The viewer's own place on the layer stack (above its dialog): ← / → are its only while nothing is
+  // on top of it — its "…" menu, a confirm, the Share or Details dialog opened from that menu. There an
+  // arrow moves through the layer's own buttons; paging the viewer under it would show one file while
+  // the dialog acts on another.
+  const layer = useLayer(true, undefined, { passive: true });
   const onKey = useEffectEvent((e: KeyboardEvent) => {
+    if (layer.blockingAbove()) return;
+    // The text, scrolled sideways by its arrows: a line wider than the stage is read that way.
+    const scroller =
+      e.target instanceof Element ? e.target.closest("[data-scrolls-sideways]") : null;
+    if (scroller && scroller.scrollWidth > scroller.clientWidth) return;
     dispatch(e, "fileViewer", {
       prevFile: (ev) => {
         ev.preventDefault();
@@ -217,8 +230,11 @@ function TextStage({ file }: { file: LibraryFile }) {
       </StateMessage>
     );
   if (!q.data) return <LoadingState className={`${STAGE} justify-center`} />;
-  // A file's last line ends in a newline; that is no line of its own.
-  const lines = q.data.text.replace(/\r?\n$/, "").split(/\r?\n/);
+  // A file's last line ends in a newline; that is no line of its own. Only the first TEXT_LINES are
+  // laid out: every line is a row of the page, and a head of short lines (a log) runs to tens of
+  // thousands of them — a stall on open and on every wrap toggle. The rest is behind Download.
+  const all = q.data.text.replace(/\r?\n$/, "").split(/\r?\n/);
+  const lines = all.length > TEXT_LINES ? all.slice(0, TEXT_LINES) : all;
   return (
     <div className={`${STAGE} flex flex-col gap-2`}>
       <div className="flex items-center gap-2 text-xs text-muted">
@@ -239,8 +255,10 @@ function TextStage({ file }: { file: LibraryFile }) {
         </IconButton>
       </div>
       <div
-        // Scrolls by keyboard too: a focusable region with a name.
+        // Scrolls by keyboard too: a focusable region with a name — sideways as well, its ← / →
+        // taken from the viewer's paging while a line runs past the edge.
         tabIndex={0}
+        data-scrolls-sideways
         role="region"
         aria-label={jobTitle(file)}
         className="min-h-0 flex-1 overflow-auto rounded-md border border-border bg-bg font-mono text-xs leading-relaxed"
@@ -262,6 +280,12 @@ function TextStage({ file }: { file: LibraryFile }) {
             </li>
           ))}
         </ol>
+        {lines.length < all.length && (
+          <p className="m-0 border-t border-border px-3 py-2 font-sans text-muted">
+            {t("files.preview.firstLines", { lines: TEXT_LINES })}{" "}
+            <LinkButton href={api.fileUrl(file.id)}>{t("files.preview.downloadWhole")}</LinkButton>
+          </p>
+        )}
       </div>
     </div>
   );