another odd thing, it seems to build stale versions of whatever my source is. For example:

  # Setup keyfile
  boot.initrd.secrets = {
    "/luks.bin" = "/luks.bin";
  };
  # Enable grub cryptodisk
  boot.loader.grub.enableCryptodisk=true;
  boot.initrd.luks.devices."luks-uuid-here".keyFile = "/luks.bin";

but it errors with:

[ERROR]   stderr) updating GRUB 2 menu...
[ERROR]   stderr) cp: cannot stat '/cryptokeyfile.bin': No such file or directory
[ERROR]   stderr) failed to create initrd secrets: No such file or directory