nix templates: factor harness-base.nix (shared scaffolding incl. gitconfig)

nix/templates/harness-base.nix

@@ -0,0 +1,35 @@
+{ pkgs, ... }:
+{
+  # Shared scaffolding for any hyperhive harness container — both
+  # sub-agents (`agent-base.nix`) and the manager (`manager.nix`) extend
+  # this. The systemd service that actually runs the harness binary
+  # differs per role and lives in the child module.
+
+  boot.isNspawnContainer = true;
+
+  nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (pkgs.lib.getName pkg) [ "claude-code" ];
+
+  environment.systemPackages = with pkgs; [
+    hyperhive
+    claude-code
+    bashInteractive
+    git
+    coreutils-full
+  ];
+  # claude's Bash tool refuses to run without a POSIX shell + $SHELL set.
+  environment.variables.SHELL = "${pkgs.bashInteractive}/bin/bash";
+
+  # Default gitconfig for any commits the harness makes. The per-agent
+  # `applied/<name>/flake.nix` overrides this with the agent's own name +
+  # email; this fallback only kicks in if the container is built straight
+  # from `agent-base` / `manager` without the per-agent extension.
+  environment.etc."gitconfig".text = ''
+    [user]
+      name = hyperhive
+      email = hyperhive@local
+    [init]
+      defaultBranch = main
+  '';
+
+  system.stateVersion = "25.11";
+}