docs: add docs/ARCHITECTURE.md with crate layout, request flow, subsystem map

README.md

@@ -36,7 +36,7 @@ Claw Code is the public Rust implementation of the `claw` CLI agent harness.
 The canonical implementation lives in [`rust/`](./rust), and the current source of truth for this repository is **ultraworkers/claw-code**.
 
 > [!IMPORTANT]
-> Start with [`USAGE.md`](./USAGE.md) for build, auth, CLI, session, and parity-harness workflows. Make `claw doctor` your first health check after building, use [`rust/README.md`](./rust/README.md) for crate-level details, read [`PARITY.md`](./PARITY.md) for the current Rust-port checkpoint, and see [`docs/container.md`](./docs/container.md) for the container-first workflow.
+> Start with [`USAGE.md`](./USAGE.md) for build, auth, CLI, session, and parity-harness workflows. Make `claw doctor` your first health check after building, use [`rust/README.md`](./rust/README.md) for crate-level details, read [`PARITY.md`](./PARITY.md) for the current Rust-port checkpoint, see [`docs/ARCHITECTURE.md`](./docs/ARCHITECTURE.md) for a high-level crate/subsystem map, and see [`docs/container.md`](./docs/container.md) for the container-first workflow.
 >
 > **ACP / Zed status:** `claw-code` does not ship an ACP/Zed daemon entrypoint yet. Run `claw acp` (or `claw --acp`) for the current status instead of guessing from source layout; `claw acp serve` is currently a discoverability alias only, and real ACP support remains tracked separately in `ROADMAP.md`.
 

docs/ARCHITECTURE.md

@@ -0,0 +1,110 @@
+# claw-code Architecture
+
+A high-level overview of how claw-code is structured. For implementation details, see source code in `rust/crates/`. For provider details, see [SUPPORTED_PROVIDERS.md](./SUPPORTED_PROVIDERS.md). For pinpoint navigation, see [ROADMAP.md](../ROADMAP.md#pinpoint-cluster-index).
+
+## Overview
+
+claw-code is a Rust-based CLI for interacting with LLM providers (Anthropic, OpenAI-compatible, xAI, DashScope, etc.). It provides:
+
+- Streaming conversation with auto-compaction
+- Tool execution (file read/write, bash, MCP)
+- Multi-provider routing
+- Session persistence
+- Parallel agent execution
+
+## Workspace Layout
+
+The Rust workspace is organized in `rust/crates/`:
+
+### Core crates
+
+- **`rusty-claude-cli`** — CLI entry point. Parses args, routes commands, manages TUI/headless modes.
+- **`runtime`** — Conversation engine. Manages session state, message history, auto-compaction, tool dispatch, hooks, MCP, and branch/lane events.
+- **`api`** — Provider abstraction. Hosts `MODEL_REGISTRY` (provider/model routing), SSE streaming, request/response handling. Providers: `anthropic`, `openai_compat`.
+- **`tools`** — Tool definitions. File I/O, bash execution, MCP integration, PDF extraction.
+
+### Support crates
+
+- **`commands`** — Parsed command dispatch layer between CLI and runtime.
+- **`plugins`** — Plugin/hook lifecycle (`hooks.rs`).
+- **`telemetry`** — Metrics and tracing instrumentation.
+- **`compat-harness`** — Parity test harness for Rust-port validation.
+- **`mock-anthropic-service`** — Local mock server for offline/test use.
+
+## Request Flow
+
+1. **CLI parse** (`rusty-claude-cli/src/main.rs`) — interprets args, env vars, settings.json
+2. **Provider selection** (`api/src/providers/mod.rs`) — routes to provider via `MODEL_REGISTRY` based on model prefix
+3. **Conversation execution** (`runtime/src/conversation.rs`) — sends to provider via SSE, receives streamed response
+4. **Tool dispatch** (`tools/src/lib.rs`) — if response includes `tool_use`, execute and feed back `tool_result`
+5. **Auto-compaction check** (`runtime/src/compact.rs`) — REACTIVE-AFTER-SUCCESS only (see #287 for preflight gap)
+6. **Output** — JSON envelope (`--output-format json`) or text (default)
+
+## Key Subsystems
+
+### Auto-compaction
+
+Triggered post-turn when `usage.input_tokens > threshold`. See:
+- Threshold via env-only (#283)
+- Reactive-not-preflight (#287, CRITICAL)
+- Manual `/compact` skip-reasons (#289)
+- Failure envelope coverage (#288)
+
+### Provider routing
+
+Hard-coded `MODEL_REGISTRY` + env-var-based auth + model-prefix heuristics. See:
+- [SUPPORTED_PROVIDERS.md](./SUPPORTED_PROVIDERS.md) for current providers
+- #285 for declarative providers/models/websearch source-of-truth
+- #245, #246 for declarative config & backend swap
+- #290, #291, #292 for transport resilience (stream-init, circuit-breaker, escalation)
+
+### Parallel agents
+
+Lane-based execution via `runtime/src/lane_events.rs`. Manifest-driven lifecycle. See:
+- #286 for detached-thread + no-heartbeat issue (CRITICAL)
+
+### Tool lifecycle / hooks
+
+Tools defined in `tools/src/`. Hook events emitted via `runtime/src/hooks.rs` and `plugins/src/hooks.rs`. See:
+- #254 (MCP refresh)
+- #268 (tool-rendering parity)
+- #274 (hook-execution-event envelope)
+- #280 (hook event tap)
+
+### Session persistence
+
+Sessions managed in `runtime/src/session.rs`. See:
+- #278 (version-comparison)
+- #279 (unknown-field policy)
+
+### CLI dispatch
+
+CLI parsing in `rusty-claude-cli/src/main.rs`. Issues:
+- #262 `--max-turns` spec
+- #267 `--cwd` runtime fix
+- #272 position-independent parsing
+- #282 env-vs-config consolidation
+
+## Build & Test
+
+See [CONTRIBUTING.md](../CONTRIBUTING.md) for build commands. Quick reference:
+
+```
+cd rust && cargo build        # Build all crates
+cd rust && cargo test         # Run all Rust tests
+```
+
+## Tracing & Debugging
+
+- **Session state:** `runtime/src/session.rs` + `~/.claw/sessions/<id>/`
+- **Provider responses:** Set `RUST_LOG=trace` for verbose SSE logs
+- **Parity checks:** Use `compat-harness` crate for Rust-port validation
+
+## Related Documents
+
+- [ROADMAP.md](../ROADMAP.md) — Pinpoints by cluster
+- [TROUBLESHOOTING.md](../TROUBLESHOOTING.md) — User-facing failure mitigation
+- [SUPPORTED_PROVIDERS.md](./SUPPORTED_PROVIDERS.md) — Provider/model details
+- [CONTRIBUTING.md](../CONTRIBUTING.md) — Pinpoint filing format
+- [PINPOINT_FILING_GUIDE.md](./PINPOINT_FILING_GUIDE.md) — Filing workflow
+- [CHANGELOG.md](../CHANGELOG.md) — Recent changes