Pin happy-coder to monorepo migration PR and wire HAPPY_CLAUDE_PATH

Track nixpkgs PR #492656 (colonelpanic8/nixpkgs happy-coder-monorepo-migration)
via a dedicated flake input and overlay until it lands in unstable. The
overlay wraps happy/happy-mcp with nodejs on PATH since the CLI spawns child
node processes via PATH lookup.

Also set HAPPY_CLAUDE_PATH on the happy wrappers and daemon so happy-coder
uses the pinned claude-code-bin instead of resolving claude from PATH.

Author: BCNelson

flake.lock

@@ -10,6 +10,9 @@
     nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
     nixpkgs-unstable-small.url = "github:nixos/nixpkgs/nixos-unstable-small";
 
+    # happy-coder PR #492656 — monorepo migration. Remove once merged into unstable.
+    nixpkgs-happy-coder.url = "github:colonelpanic8/nixpkgs/happy-coder-monorepo-migration";
+
     # Home manager - always use unstable
     home-manager-unstable.url = "github:nix-community/home-manager/master";
     home-manager-unstable.inputs.nixpkgs.follows = "nixpkgs-unstable";

flake.nix

@@ -8,9 +8,11 @@ let
     nativeBuildInputs = [ pkgs.makeWrapper ];
     postBuild = ''
       wrapProgram $out/bin/happy \
-        --set-default HAPPY_HOME_DIR ${happyHomeDir}
+        --set-default HAPPY_HOME_DIR ${happyHomeDir} \
+        --set-default HAPPY_CLAUDE_PATH ${pkgs.claude-code-bin}/bin/claude
       wrapProgram $out/bin/happy-mcp \
-        --set-default HAPPY_HOME_DIR ${happyHomeDir}
+        --set-default HAPPY_HOME_DIR ${happyHomeDir} \
+        --set-default HAPPY_CLAUDE_PATH ${pkgs.claude-code-bin}/bin/claude
     '';
     inherit (pkgs.happy-coder) meta;
   };

home-manager/bcnelson/_mixins/happy/default.nix

@@ -15,6 +15,8 @@ in
 
     authNotifyPackage = lib.mkPackageOption pkgs "happy-auth-notify" { };
 
+    claudePackage = lib.mkPackageOption pkgs "claude-code-bin" { };
+
     happyHomeDir = lib.mkOption {
       type = lib.types.str;
       default = "/home/${cfg.user}/.local/share/happy";
@@ -60,6 +62,7 @@ in
           Environment = [
             "HOME=/home/${cfg.user}"
             "HAPPY_HOME_DIR=${cfg.happyHomeDir}"
+            "HAPPY_CLAUDE_PATH=${cfg.claudePackage}/bin/claude"
           ];
           ExecStart = "${cfg.package}/bin/happy daemon start-sync";
           Restart = "on-failure";

modules/nixos/happy-daemon.nix

@@ -9,6 +9,22 @@
   # https://nixos.wiki/wiki/Overlays
   modifications = final: prev: {
     # libsForQt5.sddm = nixpkgs-unstable.libsForQt5.sddm;
+
+    # happy-coder PR #492656 — monorepo migration, pre-merge testing.
+    # Remove once the PR lands in nixpkgs-unstable.
+    # The PR's wrapper invokes node by absolute path but the CLI spawns child
+    # `node` processes via PATH lookup (e.g. `happy daemon start-sync`),
+    # so add nodejs to PATH here.
+    happy-coder = (inputs.nixpkgs-happy-coder.legacyPackages.${final.stdenv.hostPlatform.system}.happy-coder).overrideAttrs (old: {
+      nativeBuildInputs = (old.nativeBuildInputs or []) ++ [ final.makeWrapper ];
+      postFixup = (old.postFixup or "") + ''
+        wrapProgram $out/bin/happy \
+          --prefix PATH : ${final.lib.makeBinPath [ final.nodejs ]}
+        wrapProgram $out/bin/happy-mcp \
+          --prefix PATH : ${final.lib.makeBinPath [ final.nodejs ]}
+      '';
+    });
+
     claude-code-bin = prev.claude-code-bin.overrideAttrs (oldAttrs: {
       postFixup = (oldAttrs.postFixup or "") + ''
         wrapProgram $out/bin/claude \