> As a more general comment, using a GC language as the FFI target from a GC language is begging for difficult-if-not-impossible-to-debug crashes down the line.

When I was interfacing D code with a part of Unreal Engine that I think is garbage collected, I actually just took the L and copied everything into buffers on their malloc when handing stuff off to the engine. It wasn't particularly hot code so the memcpys were worth the peace of mind I found, ugly as it was.