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/data/push-router.ts

@@ -420,6 +420,9 @@ function applyCheckoutDiffUpdate(input: {
       cwd: input.message.payload.cwd,
       files: orderCheckoutDiffFiles(input.message.payload.files),
       error: input.message.payload.error,
+      ...(input.message.payload.diffTooLarge !== undefined
+        ? { diffTooLarge: input.message.payload.diffTooLarge }
+        : {}),
       requestId: `subscription:${input.message.payload.subscriptionId}`,
     },
   });
@@ -440,6 +443,9 @@ function applyCheckoutDiffSubscribeResponse(input: {
       cwd: input.message.payload.cwd,
       files: orderCheckoutDiffFiles(input.message.payload.files),
       error: input.message.payload.error,
+      ...(input.message.payload.diffTooLarge !== undefined
+        ? { diffTooLarge: input.message.payload.diffTooLarge }
+        : {}),
       requestId: input.message.payload.requestId,
     },
   });