add CLAUDE.md

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

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Nix flake providing custom packages not available in nixpkgs. Tracks `nixos-unstable`. Uses `config.allowUnfree = true`.
+
+## Build Commands
+
+```bash
+# Build a specific package
+nix build .#packages.x86_64-linux.<package-name>
+
+# Build all packages (x86_64-linux)
+./scripts/build-all.sh
+
+# Validate flake
+nix flake check
+
+# Update flake inputs
+nix flake update
+```
+
+## Structure
+
+- `flake.nix` — Defines all packages and per-package overlays. Packages are registered in `packages` and exposed via `overlays`.
+- `pkgs/<name>/default.nix` — Individual package definitions, called via `pkgs.callPackage` (or `pkgs.qt6Packages.callPackage` for Qt packages).
+- `scripts/` — Helper scripts (`build-all.sh`, `update-pob.sh`).
+
+## Adding a New Package
+
+1. Create `pkgs/<name>/default.nix` with the package derivation.
+2. Add the package to `packages` in `flake.nix` via `callPackage`.
+3. Add a per-package overlay in `flake.nix` `overlays` and include it in the `default` overlay if appropriate.
+
+## Packaging Patterns Used
+
+- **AppImage**: `appimageTools.wrapType2` (see `poe-sidekick`)
+- **Electron/Yarn**: `yarnConfigHook` + `yarnBuildHook` + `fetchYarnDeps` (see `awakened-poe-trade`)
+- **Qt6/Meson**: `qt6Packages.callPackage` + `wrapQtAppsHook` (see `path-of-building-*`)
+- **Rust/Cargo**: `rustPlatform.buildRustPackage` + `useFetchCargoVendor` (see `noita-entangled-worlds`)
+- **Binary/.NET**: `fetchurl` + `makeWrapper` with `makeLibraryPath` (see `vintagestory`)
+
+## Commit Style
+
+Imperative, prefixed with package name when relevant: `poe-sidekick: add package`, `Bump entangled worlds`.