fix(ui): a small crop frame takes smaller handles, so it can still be grabbed to move

The handles reach 10 px into the frame from every side; a frame at its minimum on a small picture
(the Downloads editor at 800 px: 41 x 23) was then nearly all handle - 74 of its 920 px still moved
it. Below 64 px on its shorter side the frame takes 12 px corners and 8 px edges: 262 px move it.

frontend/src/components/ui/CropFrame.dom.test.tsx

@@ -33,8 +33,16 @@ beforeAll(() => {
 
 const WIDE = 16 / 9;
 
-function Harness({ aspect = WIDE, ratio = null }: { aspect?: number; ratio?: number | null }) {
-  const [rect, setRect] = useState<Frac>({ x: 0.2, y: 0.2, w: 0.4, h: 0.4 });
+function Harness({
+  aspect = WIDE,
+  ratio = null,
+  start = { x: 0.2, y: 0.2, w: 0.4, h: 0.4 },
+}: {
+  aspect?: number;
+  ratio?: number | null;
+  start?: Frac;
+}) {
+  const [rect, setRect] = useState<Frac>(start);
   return (
     <div>
       <output data-testid="rect">
@@ -117,6 +125,20 @@ describe("CropFrame", () => {
     expect(document.activeElement).toBe(frame);
   });
 
+  it("shrinks its handles on a small frame, so the frame itself stays there to grab", () => {
+    const corner = () => screen.getByRole("group", { name: "common.cropFrame.se" });
+    const edge = () => document.querySelector<HTMLElement>(".cursor-ew-resize")!;
+    // 640 × 360 px of a 1600 × 900 picture: the full handles.
+    render(<Harness />);
+    expect(corner().className).toContain("size-5");
+    expect(edge().className).toContain("w-4");
+    cleanup();
+    // A 1:4 picture in that box is 225 px wide: a tenth of it is a 22 px frame.
+    render(<Harness aspect={0.25} start={{ x: 0.2, y: 0.2, w: 0.1, h: 0.5 }} />);
+    expect(corner().className).toContain("size-3");
+    expect(edge().className).toContain("w-2");
+  });
+
   it("lets a press outside the frame through to the player, and keeps one on the frame", () => {
     const click = vi.fn();
     render(

frontend/src/components/ui/CropFrame.tsx

@@ -60,6 +60,20 @@ const HANDLE_BOX: Record<CropHandle, string> = {
   e: "inset-y-3 -right-2 w-4 cursor-ew-resize",
   w: "inset-y-3 -left-2 w-4 cursor-ew-resize",
 };
+// The same on a small frame: the full handles reach 10 px into it from every side, and a frame at its
+// minimum on a small picture (40 × 23 px) was then nearly all handle, with no room left to grab it.
+const SMALL_HANDLE_BOX: Record<CropHandle, string> = {
+  nw: "-left-1.5 -top-1.5 size-3 cursor-nwse-resize",
+  ne: "-right-1.5 -top-1.5 size-3 cursor-nesw-resize",
+  sw: "-left-1.5 -bottom-1.5 size-3 cursor-nesw-resize",
+  se: "-right-1.5 -bottom-1.5 size-3 cursor-nwse-resize",
+  n: "inset-x-1.5 -top-1 h-2 cursor-ns-resize",
+  s: "inset-x-1.5 -bottom-1 h-2 cursor-ns-resize",
+  e: "inset-y-1.5 -right-1 w-2 cursor-ew-resize",
+  w: "inset-y-1.5 -left-1 w-2 cursor-ew-resize",
+};
+// Below this many px on its shorter side a frame takes the small handles.
+const SMALL_FRAME_PX = 64;
 
 type Drag = { handle: CropHandle | "move"; x: number; y: number; from: Frac };
 // Not the app's accent ring: over a video it can be any colour, and a light theme's dark-blue accent
@@ -84,6 +98,8 @@ export function CropFrame({ aspect, rect, ratio, onChange, className }: Props) {
   }, []);
 
   const pic = contentRect(box.w, box.h, aspect);
+  const small = !!pic && Math.min(rect.w * pic.width, rect.h * pic.height) < SMALL_FRAME_PX;
+  const handleBox = small ? SMALL_HANDLE_BOX : HANDLE_BOX;
 
   const begin = (handle: Drag["handle"]) => (e: PointerEvent<HTMLElement>) => {
     if (e.button !== 0) return;
@@ -180,7 +196,7 @@ export function CropFrame({ aspect, rect, ratio, onChange, className }: Props) {
               <div
                 key={h}
                 aria-hidden="true"
-                className={clsx("absolute touch-none", HANDLE_BOX[h])}
+                className={clsx("absolute touch-none", handleBox[h])}
                 {...pointer(h)}
               />
             ))}
@@ -193,13 +209,15 @@ export function CropFrame({ aspect, rect, ratio, onChange, className }: Props) {
                 data-crop={h}
                 className={clsx(
                   "absolute flex touch-none items-center justify-center rounded-xs",
-                  HANDLE_BOX[h],
+                  handleBox[h],
                   FOCUS,
                 )}
                 onKeyDown={keys(h)}
                 {...pointer(h)}
               >
-                <span className="size-2.5 rounded-xs bg-white shadow" />
+                <span
+                  className={clsx("rounded-xs bg-white shadow", small ? "size-1.5" : "size-2.5")}
+                />
               </div>
             ))}
           </div>