fix: reject oversized checkout diffs (#2488)

* fix: reject oversized checkout diffs

* fix(diff): keep large previews from disconnecting clients

The physical socket limit is an OOM backstop, not a frame-size contract. Bound structured diff construction incrementally and report oversized previews without closing the client's socket.

* fix(app): preserve oversized diff state

* fix(diff): stay within relay frame limit

---------

Co-authored-by: Mohamed Boudra <boudra.moha@gmail.com>

packages/app/src/panels/diff-panel.tsx

@@ -17,6 +17,7 @@ import {
   resolveDiffLayout,
   SharedDiffView,
 } from "@/git/diff-pane";
+import { DiffTooLargeState } from "@/git/diff-too-large-state";
 import { useCommitDiffFiles } from "@/git/use-diff-files";
 import { usePublishWorkingDiffAttachment, useWorkingDiff } from "@/git/use-working-diff";
 import { useChangesPreferences } from "@/hooks/use-changes-preferences";
@@ -120,6 +121,9 @@ function WorkingDiffBody({
   if (workingDiff.notGit) {
     return <PanelState message={t("workspace.git.diff.notRepository")} />;
   }
+  if (workingDiff.diffTooLarge) {
+    return <DiffTooLargeState />;
+  }
   if (workingDiff.diffPayloadError) {
     return (
       <PanelState message={t("panels.diff.loadError")} tone="error" testID="working-diff-error" />