self reply

the linux-backports gentree script appears (a) to have bitrotted its support for the --integrate flag; (b) to cope really badly with copying source files that don't have the writable bit set; (c) to have awful (as in, both incomprehensible and wrong) documentation; (d) to assume that everything is checked out from a git repo

Honestly, building ocaml programs was the easy bit. Deciphering intent from this wretched mess of python - well, I wouldn't mind so much if it wasn't hyped as "automatic" and "seamless" when it quite demonstrably is neither