Question on "3rd party" patches (in guix package definition)

[Andy Tai]

Hi, if I have package a and b.  A is a dependency for b or b depends on a,
and b has a patch that has to be applied to A's sources to build b.  But
B's patch is not something a would accept.  How would b be packaged in
guix?  Make a custom a-for-b to support b?  B's patch for a will never go
upstream but can that patch be kept in guix's patch directory? Normally
guix's patch directory means patches not yet merged upstream.