I don't see much choice here but to binNMU xeus, xeus-zmq, xeus-python, which will presumably break custom kernels compiled against it and an older version of nl::json. I considered just updating everything to new versions and "rolling forward", but the latest version of xeus-zmq at least has an soversion bump so probably better to request binNMUs before waiting for NEW.
Yes. I can see that there are API methods which expose nlohmann::json
(eg,
https://github.com/jupyter-xeus/xeus/blob/ebd21e9e7cfe143b4d0a6783112cc9006b456915/include/xeus/xdebugger.hpp#L55-L60)
so changes the header library are going to cause ABI breakage.
