docs: add CLAUDE.md for project guidance

- Introduced CLAUDE.md to provide comprehensive guidance on the macOS Emacs building system, including project overview, common commands, architecture details, and testing instructions.

CLAUDE.md

@@ -0,0 +1,80 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with
+code in this repository.
+
+## Project Overview
+
+macOS Emacs building system with Ruby and Go components:
+
+- **Ruby script** (`build-emacs-for-macos`): Main build script for creating
+  self-contained Emacs.app bundles
+- **Go CLI tool** (`emacs-builder`): Packaging, signing, notarization, and
+  release management
+- **Dual dependency management**: Nix (preferred) or Homebrew
+
+## Common Commands
+
+```bash
+# Environment setup (Nix preferred)
+nix develop                       # Default macOS 11 SDK
+nix develop .#macos{11-15,26}     # Target specific SDK version
+
+# Go development
+make build                        # Build emacs-builder CLI
+make test                         # Run tests with race detection
+make lint                         # Run golangci-lint
+make format                       # Format with gofumpt
+
+# Ruby development
+bundle exec rubocop               # Lint (with development group)
+
+# Build Emacs
+./build-emacs-for-macos           # Build from master
+./build-emacs-for-macos emacs-29.4
+```
+
+## Architecture
+
+### Ruby Build Script (`build-emacs-for-macos`)
+
+Single-file Ruby script (~2500 lines) that:
+
+- Downloads source tarballs from emacs-mirror/emacs on GitHub
+- Configures and compiles Emacs with native-comp, tree-sitter support
+- Creates self-contained .app bundles by embedding/relinking dependencies
+- Uses `ruby-macho` gem for Mach-O binary manipulation (RPATH handling)
+
+### Go CLI (`cmd/emacs-builder/`)
+
+Uses `urfave/cli/v2` framework. Key packages in `pkg/`:
+
+- `cli/`: Commands (plan, sign, sign-files, notarize, package, release, cask)
+- `sign/`: macOS code signing via `codesign`
+- `notarize/`: Apple notarization workflow via `notarytool`
+- `release/`: GitHub release management
+- `dmgbuild/`: DMG creation using Python dmgbuild
+- `plan/`: Build plan JSON parsing and management
+
+### Nix Environment (`flake.nix`)
+
+- Multi-SDK support: macOS 11-15, 26 via `.#macos{11,12,13,14,15,26}`
+- Excludes ncurses intentionally (links against system version for TUI)
+- Sets `MACOSX_DEPLOYMENT_TARGET`, `DEVELOPER_DIR`, `NIX_LIBGCCJIT_*`
+
+## Testing
+
+```bash
+make test                         # All Go tests
+go test ./pkg/release/...         # Single package
+go test -run TestName ./pkg/...   # Single test
+```
+
+Tests use `_test.go` suffix alongside source files.
+
+## Working Directories
+
+- `sources/`: Downloaded/extracted Emacs source (gitignored)
+- `builds/`: Build outputs and .app bundles (gitignored)
+- `patches/`: Emacs patches applied during build
+- `bin/`: Built Go binaries (gitignored)

Makefile

@@ -141,10 +141,10 @@ nix-flake-update:
 
 .SILENT: flake-package-versions
 flake-package-versions:
-	nix develop --command -- bash -c \
+	nix develop --command bash -c \
 		'nix derivation show \
 			$$(echo $$PATH | tr ":" "\n" | grep "/nix/store" | sort -u) \
-			| jq -r ".[].name" | sort -u'
+			| jq -r ".derivations[].name" | sort -u'
 
 flake.pkgs: flake.nix flake.lock
 	$(MAKE) flake-package-versions > "$@"

flake.lock

@@ -20,11 +20,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1757545623,
+        "lastModified": 1767313136,
-        "narHash": "sha256-mCxPABZ6jRjUQx3bPP4vjA68ETbPLNz9V2pk9tO7pRQ=",
+        "narHash": "sha256-16KkgfdYqjaeRGBaYsNrhPRRENs0qzkQVUooNHtoy2w=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "8cd5ce828d5d1d16feff37340171a98fc3bf6526",
+        "rev": "ac62194c3917d5f474c1a844b6fd6da2db95077d",
         "type": "github"
       },
       "original": {

flake.nix

@@ -6,16 +6,32 @@
     flake-utils.url = "github:numtide/flake-utils";
   };
 
-  outputs = { self, nixpkgs, flake-utils }:
+  outputs =
-    flake-utils.lib.eachDefaultSystem (system:
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
 
         # List of supported macOS SDK versions.
-        sdk_versions = [ "11" "12" "13" "14" "15" ];
+        sdk_versions = [
+          "11"
+          "12"
+          "13"
+          "14"
+          "15"
+          "26"
+        ];
         default_sdk_version = "11";
 
-        mkDevShell = { macos_version ? default_sdk_version }:
+        mkDevShell =
+          {
+            macos_version ? default_sdk_version,
+          }:
           let
             apple_sdk = pkgs.${"apple-sdk_${macos_version}"};
           in

flake.pkgs

@@ -13,7 +13,7 @@ coreutils-9.7
 curl-8.14.1
 dbus-1.14.10
 diffutils-3.12
-expat-2.7.1
+expat-2.7.3
 file-5.45
 findutils-4.10.0
 fontconfig-2.16.0
@@ -53,7 +53,7 @@ libxml2-2.13.8
 mailutils-3.18
 nettle-3.10.1
 nghttp2-1.65.0
-openssl-3.4.2
+openssl-3.4.3
 patch-2.7.6
 pkg-config-wrapper-0.29.2
 python3-3.13.5