fix(vcs): remember the diff window's size between openings (#2328) (#2353)

The modal-commit diff dialog always reopened at its default 1100x720.
Pass the persisted size as the dialog's initialSize and save it when a
resize ends, like the Find in Files popup already does.

src/features/vcs/__tests__/diffDialog.test.tsx

@@ -23,7 +23,7 @@ import { ChangesTree, nodeMenu } from "../CommitView";
 import type { ChangeNode } from "../changes";
 import { VcsDialogHost } from "../dialogs";
 import { useVcs } from "../store";
-import { openDiffDialog } from "../diffDialog";
+import { loadDiffDialogSize, openDiffDialog } from "../diffDialog";
 
 const modified = (path: string) => ({
   path,
@@ -116,6 +116,28 @@ describe("Commit dialog diff window (#1863)", () => {
     await screen.findByRole("dialog", { name: "b.ts (HEAD ↔ Your version)" });
   });
 
+  it("remembers the resized size for the next opening (#2328)", async () => {
+    render(<VcsDialogHost />);
+    let close: () => void = () => {};
+    act(() => {
+      close = openDiffDialog({ path: "/p/a.ts", left: { type: "rev", rev: "HEAD" }, right: { type: "worktree" } });
+    });
+    await diffDialogs();
+    // Drag the corner grip; jsdom reports a zero rect so the dialog clamps to its
+    // minimums — what matters is that the resize end is persisted.
+    fireEvent.pointerDown(screen.getByRole("separator", { name: "Resize" }), { button: 0, clientX: 0, clientY: 0 });
+    fireEvent.pointerMove(window, { buttons: 1, clientX: 100, clientY: 80 });
+    fireEvent.pointerUp(window);
+    expect(loadDiffDialogSize()).toEqual({ w: 480, h: 280 });
+    act(() => close());
+    // A fresh open starts at the remembered size rather than the default.
+    act(() => {
+      close = openDiffDialog({ path: "/p/a.ts", left: { type: "rev", rev: "HEAD" }, right: { type: "worktree" } });
+    });
+    const reopened = await diffDialogs();
+    expect([reopened.style.width, reopened.style.height]).toEqual(["480px", "280px"]);
+  });
+
   it("closes on Jump to Source so the editor it opens is not hidden behind it", async () => {
     render(
       <>

src/features/vcs/diffDialog.tsx

@@ -15,6 +15,26 @@ import { diffInput, diffTitle, type DiffData } from "./diffInput";
 import { openDialog } from "./dialogs";
 import { GitMergeDiff } from "./GitMergeDiff";
 
+const SIZE_KEY = "openidea.vcs.diffDialogSize";
+
+/** The diff window's last size (#2328); null on first run, clamped to the window by Dialog. */
+export function loadDiffDialogSize(): { w: number; h: number } | null {
+  try {
+    const v = JSON.parse(localStorage.getItem(SIZE_KEY) ?? "null") as { w?: unknown; h?: unknown } | null;
+    return typeof v?.w === "number" && typeof v.h === "number" ? { w: v.w, h: v.h } : null;
+  } catch {
+    return null;
+  }
+}
+
+export function saveDiffDialogSize(size: { w: number; h: number }) {
+  try {
+    localStorage.setItem(SIZE_KEY, JSON.stringify(size));
+  } catch {
+    // Private mode etc. — the size just isn't remembered.
+  }
+}
+
 /** The open diff dialog's close function (one diff window at a time, as in IDEA). */
 let shown: (() => void) | null = null;
 
@@ -52,6 +72,14 @@ export function openMergeDiffDialog(input: EditorInput): () => void {
 
 function FrontWindow({ title, onClose, children }: { title: string; onClose: () => void; children: ReactNode }) {
   const body = useRef<HTMLDivElement>(null);
+  // The size the user last resized the diff window to (#2328), else the usual default.
+  const [initialSize] = useState(
+    () =>
+      loadDiffDialogSize() ?? {
+        w: Math.min(1100, globalThis.innerWidth - 64),
+        h: Math.min(720, globalThis.innerHeight - 64),
+      },
+  );
   useEffect(
     () =>
       registerKeyClaim((e, stroke) => {
@@ -74,7 +102,8 @@ function FrontWindow({ title, onClose, children }: { title: string; onClose: ()
       resizable="both"
       minWidth={480}
       minHeight={280}
-      initialSize={{ w: Math.min(1100, globalThis.innerWidth - 64), h: Math.min(720, globalThis.innerHeight - 64) }}
+      initialSize={initialSize}
+      onResized={saveDiffDialogSize}
       buttons={[{ label: "Close", role: "cancel" }]}
     >
       <div