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/git/use-diff-query.ts

@@ -92,6 +92,7 @@ export function useCheckoutDiffQuery({
   return {
     files: payload?.files ?? [],
     payloadError,
+    diffTooLarge: payload?.diffTooLarge === true,
     isLoading: payload === null && enabled && isConnected,
     isFetching: false,
     isError: Boolean(payloadError),