feat: Rust port of Claude Code CLI

Crates:
- api: Anthropic Messages API client with SSE streaming
- tools: Claude-compatible tool implementations (Bash, Read, Write, Edit, Glob, Grep + extended suite)
- runtime: conversation loop, session persistence, permissions, system prompt builder
- rusty-claude-cli: terminal UI with markdown rendering, syntax highlighting, spinners
- commands: subcommand definitions
- compat-harness: upstream TS parity verification

All crates pass cargo fmt/clippy/test.

rust/README.md

@@ -0,0 +1,54 @@
+# Rust port foundation
+
+This directory contains the first compatibility-first Rust foundation for a drop-in Claude Code CLI replacement.
+
+## Current milestone
+
+This initial milestone focuses on **harness-first scaffolding**, not full feature parity:
+
+- a Cargo workspace aligned to major upstream seams
+- a placeholder CLI crate (`rusty-claude-cli`)
+- runtime, command, and tool registry skeleton crates
+- a `compat-harness` crate that reads the upstream TypeScript sources in `../src/`
+- tests that prove upstream manifests/bootstrap hints can be extracted from the leaked TypeScript codebase
+
+## Workspace layout
+
+```text
+rust/
+├── Cargo.toml
+├── README.md
+├── crates/
+│   ├── rusty-claude-cli/
+│   ├── runtime/
+│   ├── commands/
+│   ├── tools/
+│   └── compat-harness/
+└── tests/
+```
+
+## How to use
+
+From this directory:
+
+```bash
+cargo fmt --all
+cargo check --workspace
+cargo test --workspace
+cargo run -p rusty-claude-cli -- --help
+cargo run -p rusty-claude-cli -- dump-manifests
+cargo run -p rusty-claude-cli -- bootstrap-plan
+```
+
+## Design notes
+
+The shape follows the PRD's harness-first recommendation:
+
+1. Extract observable upstream command/tool/bootstrap facts first.
+2. Keep Rust module boundaries recognizable.
+3. Grow runtime compatibility behind proof artifacts.
+4. Document explicit gaps instead of implying drop-in parity too early.
+
+## Relationship to the root README
+
+The repository root README explains the leaked TypeScript codebase. This document tracks the Rust replacement effort that lives in `rust/`.