fix: resolve readline conflict, implement /reset, update model defaults in ch08

[octo-patch]

Problem

Chapter 08 (08-build-your-own.md) contains several bugs in the tutorial code that readers encounter when following along:

1. Readline conflict — index.ts creates a readline.Interface and passes it to PermissionChecker, but CLI's constructor also creates its own readline.Interface. Two competing readline instances both attached to stdin causes garbled input handling in interactive mode.

2. /reset command does nothing — The /reset case in CLI.ts only logs [会话已重置] but never calls any actual reset. The comment even acknowledges this as a TODO (// 这里通过事件或直接调用实现).

3. Retired model in mermaid diagram — The final architecture diagram references claude-3-7-sonnet, which was retired on February 19, 2026.

4. Outdated default model — Default model is claude-opus-4-5 (legacy); claude-sonnet-4-6 is the current recommended model.

5. Unusual max_tokens value — 8096 should be 8192 (standard power-of-two).

Solution

• CLI constructor now accepts an optional readline.Interface parameter; when provided, it reuses the shared instance instead of creating a new one. index.ts passes the same rl to both PermissionChecker and CLI.
• AgentLoop.reset() method added, delegating to ContextManager.reset(). The /reset case in CLI now calls this.agent.reset().
• Default model updated from claude-opus-4-5 to claude-sonnet-4-6 in both AgentLoop.ts and index.ts code blocks.
• Mermaid diagram updated from retired claude-3-7-sonnet to claude-sonnet-4-6.
• max_tokens corrected from 8096 to 8192.

Testing

All changes are in the tutorial markdown file. The code snippets were manually verified for correctness against the Anthropic TypeScript SDK API surface.