feat(models): add tool use support to OpenAIClient

src/models/openai.test.ts

@@ -1,14 +1,17 @@
 import { describe, it, expect, vi } from 'vitest';
 import { OpenAIClient } from './openai.js';
 
+// Shared mock function so we can override per-test
+const mockCreate = vi.fn().mockResolvedValue({
+  choices: [{ message: { content: 'Hello from GPT!' }, finish_reason: 'stop' }],
+  usage: { prompt_tokens: 10, completion_tokens: 5 },
+});
+
 vi.mock('openai', () => ({
   default: vi.fn().mockImplementation(() => ({
     chat: {
       completions: {
-        create: vi.fn().mockResolvedValue({
-          choices: [{ message: { content: 'Hello from GPT!' }, finish_reason: 'stop' }],
-          usage: { prompt_tokens: 10, completion_tokens: 5 },
-        }),
+        create: mockCreate,
       },
     },
   })),
@@ -31,3 +34,44 @@ describe('OpenAIClient', () => {
     expect(response.usage.outputTokens).toBe(5);
   });
 });
+
+describe('OpenAIClient tool use', () => {
+  it('passes tools to API and parses tool_calls response', async () => {
+    mockCreate.mockResolvedValueOnce({
+      choices: [{
+        message: {
+          content: null,
+          tool_calls: [{
+            id: 'call_1',
+            type: 'function',
+            function: { name: 'shell.exec', arguments: '{"command":"ls"}' },
+          }],
+        },
+        finish_reason: 'tool_calls',
+      }],
+      usage: { prompt_tokens: 20, completion_tokens: 15 },
+    });
+
+    const client = new OpenAIClient({
+      apiKey: 'test-key',
+      model: 'gpt-4o',
+    });
+
+    const response = await client.chat({
+      messages: [{ role: 'user', content: 'list files' }],
+      tools: [{
+        name: 'shell.exec',
+        description: 'Run shell command',
+        input_schema: { type: 'object', properties: { command: { type: 'string' } }, required: ['command'] },
+      }],
+    });
+
+    expect(response.stopReason).toBe('tool_calls');
+    expect(response.toolCalls).toHaveLength(1);
+    expect(response.toolCalls![0]).toEqual({
+      id: 'call_1',
+      name: 'shell.exec',
+      args: { command: 'ls' },
+    });
+  });
+});