Add concrete Langfuse tracer and prompt gateway

test/core/langfuse/LangfusePromptGateway.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it, vi } from 'vitest';
+
+const compile = vi.fn().mockReturnValue([{ role: 'user', content: 'hi' }]);
+const getPrompt = vi.fn().mockResolvedValue({ name: 'greet', version: 2, config: { model: 'llama3' }, compile });
+
+vi.mock('langfuse', () => ({
+  Langfuse: vi.fn().mockImplementation(() => ({ getPrompt })),
+}));
+
+import { LangfusePromptGateway } from '../../../src/core/langfuse/LangfusePromptGateway';
+
+describe('LangfusePromptGateway', () => {
+  it('fetches a chat prompt from Langfuse bypassing the SDK cache, and adapts it to RawPrompt', async () => {
+    const gateway = new LangfusePromptGateway({ publicKey: 'pk', secretKey: 'sk', baseUrl: 'http://lf' });
+    const raw = await gateway.fetch('greet');
+
+    expect(getPrompt).toHaveBeenCalledWith('greet', undefined, { type: 'chat', cacheTtlSeconds: 0 });
+    expect(raw.name).toBe('greet');
+    expect(raw.version).toBe(2);
+    expect(raw.config).toEqual({ model: 'llama3' });
+    expect(raw.compile({ who: 'alice' })).toEqual([{ role: 'user', content: 'hi' }]);
+  });
+});