Add CLAUDE.md with project guidance for Claude Code

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

Author: fsouza

CLAUDE.md

@@ -0,0 +1,56 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+prettierd is a daemon-based wrapper around Prettier that provides fast code formatting
+for editor integration. It uses [core_d.js](https://github.com/mantoni/core_d.js) to
+run Prettier as a persistent background process, avoiding repeated Node.js startup
+overhead. Published as `@fsouza/prettierd` on npm.
+
+## Commands
+
+- `yarn build` — compile TypeScript (`tsc -b`, outputs to `dist/`)
+- `yarn prettier:check` — verify code formatting
+- `yarn prettier:fix` — auto-format all code
+- `yarn start` — start the prettierd daemon
+
+There is no test suite. CI runs `prettier:check`, `build`, and then starts the daemon
+to verify it works.
+
+## Architecture
+
+```
+bin/prettierd          Shell entry point (sets FORCE_COLOR=0, requires dist/prettierd.js)
+    ↓
+src/prettierd.ts       CLI orchestration: parses args, sets up env vars, manages daemon
+    ├─→ src/args.ts         CLI argument definitions and help display
+    ├─→ src/get-stdin.ts    Vendored stdin reader (from get-stdin package)
+    ├─→ src/service.ts      Core formatting service invoked by core_d daemon
+    └─→ core_d              External daemon lifecycle manager (start/stop/restart/status)
+```
+
+**prettierd.ts** — Processes CLI arguments into actions (INVOKE_CORE_D, STOP,
+PRINT_VERSION, etc.), determines the runtime directory (XDG_RUNTIME_DIR or TMPDIR or
+HOME), and forwards `PRETTIERD_*` environment variables from client to the daemon
+service.
+
+**service.ts** — The service module loaded by core_d. Handles:
+- Prettier resolution: tries local project prettier first, falls back to bundled.
+  `PRETTIERD_LOCAL_PRETTIER_ONLY` env var disables the fallback.
+- Config resolution chain: explicit config path → `PRETTIERD_DEFAULT_CONFIG` env var →
+  `prettier.resolveConfig()` with editorconfig support.
+- Config precedence modes: `cli-override` (default), `file-override`, `prefer-file`.
+- Two tasks: `format` (default) and `check`.
+
+**Daemon model** — One daemon instance per working directory, identified by an encoded
+dotfile name (`.prettierd@{encoded_cwd}`). Invocation: content is piped via stdin with
+the filename as the first argument.
+
+## Code Conventions
+
+- Strict TypeScript (`strict: true` plus all additional strict flags in tsconfig.json)
+- ES2018 target, CommonJS modules
+- 2-space indentation, formatting enforced by Prettier
+- Type declarations for untyped dependencies live in `src/types/`