diff --git a/CLAUDE.md b/CLAUDE.md
index 59482d7a8..636704e6f 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -1,7 +1,24 @@
-# Arc
+# CLAUDE.md
 
-## Dev servers
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
 
+## Build and test commands
+
+### Rust
+- `cargo build --workspace` — build all crates
+- `cargo test --workspace` — run all tests
+- `cargo test -p arc-api` — test a single crate
+- `cargo test -p arc-workflows -- test_name` — run a single test
+- `cargo fmt --check --all` — check formatting
+- `cargo clippy --workspace -- -D warnings` — lint
+
+### TypeScript (arc-web)
+- `cd apps/arc-web && bun run dev` — start React dev server
+- `cd apps/arc-web && bun test` — run tests
+- `cd apps/arc-web && bun run typecheck` — type check
+- `cd apps/arc-web && bun run build` — production build
+
+### Dev servers
 1. `arc serve` — starts the Rust API server (demo mode is per-request via `X-Arc-Demo: 1` header)
 2. `cd apps/arc-web && bun run dev` — starts the React dev server
 
@@ -15,6 +32,44 @@ The OpenAPI spec at `docs/api-reference/arc-api.yaml` is the source of truth for
 4. `cargo test -p arc-api` — conformance test catches spec/router drift
 5. `cd packages/arc-api-client && bun run generate` — regenerates TypeScript Axios client
 
+## Architecture
+
+Arc is an AI-powered workflow orchestration platform. Workflows are defined as DOT graphs, where each node is a stage (agent, prompt, command, conditional, human, parallel, etc.) executed by the workflow engine.
+
+### Rust crates (`crates/`)
+- **arc-cli** — CLI entry point. Commands: `run`, `exec`, `serve`, `validate`, `parse`, `cp`, `model`, `doctor`, `setup`, `ps`, `system prune`, `llm`
+- **arc-workflows** — Core workflow engine. Parses DOT graphs, runs stages, manages checkpoints/resume, hooks, retros, and human-in-the-loop interactions
+- **arc-agent** — AI coding agent with tool use (Bash, Read, Write, Edit, Glob, Grep, WebFetch). `Sandbox` trait abstracts execution environments
+- **arc-api** — Axum HTTP server. Routes for runs, sessions, models, completions, usage. SSE event streaming. Demo mode via header
+- **arc-exe** — SSH-based sandbox implementation (`ExeSandbox`)
+- **arc-sprites** — Sprites VM sandbox implementation via `sprite` CLI
+- **arc-llm** — Unified LLM client with providers: Anthropic, OpenAI, Gemini, OpenAI-compatible, plus retry/middleware/streaming
+- **arc-types** — Auto-generated Rust types from OpenAPI spec (build.rs + typify)
+- **arc-github** — GitHub App auth (JWT signing, installation tokens, PR creation)
+- **arc-db** — SQLite with WAL mode, schema migrations
+- **arc-mcp** — Model Context Protocol client/server
+- **arc-slack** — Slack integration (socket mode, blocks API)
+- **arc-devcontainer** — Parses `.devcontainer/devcontainer.json` for container setup
+- **arc-git-storage** — Git-based storage with branch store and snapshots
+- **arc-util** — Shared utilities (redaction, telemetry, terminal formatting)
+
+### TypeScript (`apps/` and `packages/`)
+- **apps/arc-web** — React 19 + React Router + Vite + Tailwind CSS frontend
+- **packages/arc-api-client** — Auto-generated TypeScript Axios client from OpenAPI spec
+
+### Key design patterns
+- **Sandbox trait** — Uniform interface for local, Docker, SSH (ExeSandbox), Sprites, and Daytona execution environments
+- **DOT graph workflows** — Stages and transitions defined as DOT graph attributes
+- **OpenAPI-first** — `arc-api.yaml` drives both Rust type generation (typify) and TypeScript client generation (openapi-generator)
+- **Checkpoint/resume** — Workflows can be paused, checkpointed, and resumed
+
+## Logging and events
+
+When working on Rust crates, read the relevant strategy doc **before** making changes:
+
+- **`docs-internal/logging-strategy.md`** — read when adding `tracing` calls (`info!`, `debug!`, `warn!`, `error!`), working on error handling paths, or adding new operations that should be observable
+- **`docs-internal/events-strategy.md`** — read when adding or modifying `WorkflowRunEvent` variants, touching `EventEmitter`/`emit()`, changing `progress.jsonl` output, or adding new workflow stage types
+
 ## Shell quoting in sandbox code
 
 When interpolating values into shell command strings (in `arc-exe` and `arc-workflows`), always use the `shell_quote()` helper (backed by `shlex::try_quote`). Never use manual `replace('\'', "'\\''")` or unquoted interpolation. This applies to file paths, branch names, URLs, env vars, image names, glob patterns, and any other user-controlled input assembled into a shell script.