I could hardly believe it, but I got a working build eventually with stock nixpkgs. This comes from taking a legacy flake which is super complicated as a starting point. As background, I’m rewriting the flake with a flat and simple structure.
I’m still in the process of figuring out why exactly this is working. The main change I made is adding the SDK override and updating nixpkgs to a include a higher version of go to address a _SecTrustEvaluateWithError I got when using SDK 10_12 throughout.
There’s another bit which may have an influence holochain/nix/modules/darwin.nix at 00cf54944968c3bc1b5d9ce0ae9eb0c28529df2e · jost-s/holochain · GitHub.
Once I’ve come to understand it, I’ll report back.