* 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>