feat: add Anthropic client wrapper

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/models/anthropic.test.ts

@@ -0,0 +1,33 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { AnthropicClient } from './anthropic.js';
+
+// Mock the SDK
+vi.mock('@anthropic-ai/sdk', () => ({
+  default: vi.fn().mockImplementation(() => ({
+    messages: {
+      create: vi.fn().mockResolvedValue({
+        content: [{ type: 'text', text: 'Hello from Claude!' }],
+        stop_reason: 'end_turn',
+        usage: { input_tokens: 10, output_tokens: 5 },
+      }),
+    },
+  })),
+}));
+
+describe('AnthropicClient', () => {
+  it('sends messages and returns response', async () => {
+    const client = new AnthropicClient({
+      apiKey: 'test-key',
+      model: 'claude-sonnet-4-20250514',
+    });
+
+    const response = await client.chat({
+      messages: [{ role: 'user', content: 'Hello' }],
+    });
+
+    expect(response.content).toBe('Hello from Claude!');
+    expect(response.stopReason).toBe('end_turn');
+    expect(response.usage.inputTokens).toBe(10);
+    expect(response.usage.outputTokens).toBe(5);
+  });
+});

src/models/anthropic.ts

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+import Anthropic from '@anthropic-ai/sdk';
+import type { ChatRequest, ChatResponse, ModelClient } from './types.js';
+
+export interface AnthropicClientConfig {
+  apiKey?: string;  // Falls back to ANTHROPIC_API_KEY env var
+  model: string;
+  maxTokens?: number;
+}
+
+export class AnthropicClient implements ModelClient {
+  private client: Anthropic;
+  private model: string;
+  private defaultMaxTokens: number;
+
+  constructor(config: AnthropicClientConfig) {
+    this.client = new Anthropic({
+      apiKey: config.apiKey,
+    });
+    this.model = config.model;
+    this.defaultMaxTokens = config.maxTokens ?? 4096;
+  }
+
+  async chat(request: ChatRequest): Promise<ChatResponse> {
+    const response = await this.client.messages.create({
+      model: this.model,
+      max_tokens: request.maxTokens ?? this.defaultMaxTokens,
+      system: request.system,
+      messages: request.messages.map((m) => ({
+        role: m.role,
+        content: m.content,
+      })),
+    });
+
+    const textContent = response.content.find((c) => c.type === 'text');
+    const content = textContent?.type === 'text' ? textContent.text : '';
+
+    return {
+      content,
+      stopReason: response.stop_reason ?? 'end_turn',
+      usage: {
+        inputTokens: response.usage.input_tokens,
+        outputTokens: response.usage.output_tokens,
+      },
+    };
+  }
+}

src/models/index.ts

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+export { AnthropicClient, type AnthropicClientConfig } from './anthropic.js';
+export type { Message, ChatRequest, ChatResponse, ModelClient } from './types.js';

src/models/types.ts

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+export interface Message {
+  role: 'user' | 'assistant';
+  content: string;
+}
+
+export interface ChatRequest {
+  messages: Message[];
+  system?: string;
+  maxTokens?: number;
+}
+
+export interface ChatResponse {
+  content: string;
+  stopReason: 'end_turn' | 'max_tokens' | 'stop_sequence' | string;
+  usage: {
+    inputTokens: number;
+    outputTokens: number;
+  };
+}
+
+export interface ModelClient {
+  chat(request: ChatRequest): Promise<ChatResponse>;
+}