like, nothing's printed, not even []?

Nope, nothing :-\

can you put out what you have written again?

Yeah it wouldn't surprise me if it were something like me being no smort with the syntax! And ya be correct in that my transcription had one too many =, though be assured that wasn't/ain't the reality.

Here be the current state of things;

/etc/nixos/flake.nix (snip)

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
    # ...
    git-nixpkgs = {
      type = "path";
      path = "/home/s0ands0/git/hub/NixOS/nixpkgs";
    };
  };

  outputs = { self, nixpkgs, ... }@attrs: {
    nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      specialArgs = attrs;
      modules = [
        ./configuration.nix
        # ...
      ];
    };
  };
}

/etc/nixos/configuration.nix (snip)

{
  pkgs,
  git-nixpkgs,
  ...
}:

let
  # git-nixpkgs = import /home/s0ands0/git/hub/NixOS/nixpkgs { };
in
lib.warn (builtins.toString (builtins.attrNames git-nixpkgs))
{
  # ...
  services.dictd = {
    enable = true;

    # DBs = with git-nixpkgs.pkgs.dictDBs; [
    DBs = with git-nixpkgs.legacyPackages.${pkgs.system}.dictDBs; [
      gcide
    ];
  };
}

Now at the rebuild phase, which uh takes a few minutes;

nixos-rebuild test --impure --flake .
#> warning: Git tree '/etc/nixos' is dirty
#> copying "/home/s0ands0/git/hub/NixOS/nixpkgs" to the store
#> ...
#> copying "/nix/store/<HASH>-source/" to the store
#> ...

Woot!

#> evaluation warning: _type checks devShells ... legacyPackages...
#> Done. The new configuration is /nix/store/<HASH>-....

Thank you!!!! I must have been battling some typo for the last 5 (or more) hours and ya solved it in minutes x-)

what does it mean that a package listed in search.nixos.org gives this:

error: cannot find flake 'flake:hledger' in the flake registries

what does it mean that a package listed in search.nixos.org gives this when using nix profile install:

error: cannot find flake 'flake:hledger' in the flake registries