I want to also add a few details regarding breakpointHook. It is a really powerful debug hook by @Mic92.
It is enough to put pkgs.breakpointHook into your buildInputs to get it working. In the case of a failure there is an exact “connection” command printed out to the console. You can use this command (cntr) to attach a shell into the build environment. To use it you have to be able to run sudo along with cntr (so you should install cntr package before ;-)).
You can find more interesting details in the @Mic92 NixCon presentation: https://www.youtube.com/watch?v=ULqoCjANK-I