Initial System76 Launch 3 keyboard firmware project

Nix flake with devShell providing qmk CLI for firmware development.
Custom keymap (copy of default) symlinked into QMK tree on shell entry.

Setup: nix develop, then qmk setup system76/qmk_firmware
Build: qmk compile -kb system76/launch_3 -km custom

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

flake.nix

@@ -0,0 +1,62 @@
+{
+  description = "System76 Launch 3 keyboard firmware";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs }:
+    let
+      supportedSystems = [ "x86_64-linux" "aarch64-linux" ];
+      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+    in {
+      devShells = forAllSystems (system:
+        let pkgs = nixpkgs.legacyPackages.${system};
+        in {
+          default = pkgs.mkShell {
+            name = "launch3-firmware";
+
+            packages = [
+              pkgs.qmk
+              pkgs.python3Packages.appdirs
+            ];
+
+            shellHook = ''
+              export QMK_HOME="$PWD/qmk_firmware"
+
+              # Symlink tracked keymap into QMK tree
+              if [ -d "$QMK_HOME/keyboards/system76/launch_3" ]; then
+                ln -sfn "$PWD/keymaps/custom" "$QMK_HOME/keyboards/system76/launch_3/keymaps/custom"
+              fi
+            '';
+          };
+        });
+
+      packages = forAllSystems (system:
+        let pkgs = nixpkgs.legacyPackages.${system};
+        in {
+          firmware = pkgs.stdenv.mkDerivation {
+            pname = "launch3-firmware";
+            version = "0.1.0";
+
+            src = ./qmk_firmware;
+
+            nativeBuildInputs = [
+              pkgs.qmk
+              pkgs.python3Packages.appdirs
+            ];
+
+            buildPhase = ''
+              export HOME=$(mktemp -d)
+              export QMK_HOME="$PWD"
+              qmk compile -kb system76/launch_3 -km custom
+            '';
+
+            installPhase = ''
+              mkdir -p $out
+              cp *.uf2 $out/ 2>/dev/null || cp .build/*.uf2 $out/
+            '';
+          };
+        });
+    };
+}