diff --git a/Cursor++/src/server/handlers/llm/anthropic.ts b/Cursor++/src/server/handlers/llm/anthropic.ts
index d271c0a..13253cc 100644
--- a/Cursor++/src/server/handlers/llm/anthropic.ts
+++ b/Cursor++/src/server/handlers/llm/anthropic.ts
@@ -89,6 +89,13 @@ export class AnthropicProvider implements LLMProvider {
             stream: true,
         };
 
+        // 会话亲和: 透传 conversationId 至 metadata.user_id, 供下游网关做
+        // 会话级粘性路由 (session affinity)。官方客户端 Claude Code 同样在该
+        // 字段中携带 session 维度; 缺省时不注入, 保持请求体不变。
+        if (request.conversationId) {
+            params.metadata = { user_id: request.conversationId };
+        }
+
         if (cached.system) {
             params.system = cached.system;
         }
diff --git a/Cursor++/src/server/tests/anthropicAffinity.test.ts b/Cursor++/src/server/tests/anthropicAffinity.test.ts
new file mode 100644
index 0000000..b1c7a71
--- /dev/null
+++ b/Cursor++/src/server/tests/anthropicAffinity.test.ts
@@ -0,0 +1,75 @@
+import type Anthropic from '@anthropic-ai/sdk'
+import type { ProviderEntry } from '../data/defaults'
+import { describe, expect, it } from 'vitest'
+import { AnthropicProvider } from '../handlers/llm/anthropic'
+
+// 会话亲和契约: conversationId 必须进入请求体 metadata.user_id,
+// 供下游网关做会话级粘性路由; 未提供时不得注入空 metadata。
+// 通过拦截 SDK client 的 messages.stream 参数直接断言 (不发起真实请求)。
+
+type CapturedParams = Anthropic.MessageCreateParamsStreaming
+
+function makeProvider(): { provider: AnthropicProvider, captured: CapturedParams[] } {
+  const captured: CapturedParams[] = []
+  const fakeStream = (params: CapturedParams) => {
+    captured.push(params)
+    throw new Error('STOP_TEST')
+  }
+  const client = {
+    messages: { stream: fakeStream },
+    beta: { messages: { stream: fakeStream } },
+  } as unknown as Anthropic
+  const entry = {
+    id: 'test',
+    name: 'Test',
+    type: 'anthropic',
+    baseUrl: 'https://api.example.com',
+    auth: { kind: 'apiKey', value: 'sk-test' },
+    models: [],
+  } as unknown as ProviderEntry
+  const provider = new AnthropicProvider(entry)
+  // @ts-expect-error 访问私有字段替换 client
+  provider.client = client
+  return { provider, captured }
+}
+
+async function consumeStream(provider: AnthropicProvider, conversationId?: string): Promise<void> {
+  const stream = provider.stream({
+    model: 'test-model',
+    maxTokens: 1024,
+    messages: [{ role: 'user', content: 'hi' }],
+    ...(conversationId ? { conversationId } : {}),
+  })
+  try {
+    for await (const _ of stream) {
+      // 迭代到 fakeStream 抛错为止
+    }
+  }
+  catch (err) {
+    if (!(err instanceof Error && err.message === 'STOP_TEST'))
+      throw err
+  }
+}
+
+describe('anthropic conversation affinity (metadata.user_id)', () => {
+  it('passes conversationId as metadata.user_id when present', async () => {
+    const { provider, captured } = makeProvider()
+    await consumeStream(provider, 'conv-affinity-42')
+    expect(captured.length).toBe(1)
+    expect(captured[0].metadata).toEqual({ user_id: 'conv-affinity-42' })
+  })
+
+  it('omits metadata entirely when conversationId is absent', async () => {
+    const { provider, captured } = makeProvider()
+    await consumeStream(provider)
+    expect(captured.length).toBe(1)
+    expect(captured[0].metadata).toBeUndefined()
+  })
+
+  it('keeps a distinct user_id per conversation (no cross-session leakage)', async () => {
+    const { provider, captured } = makeProvider()
+    await consumeStream(provider, 'conv-A')
+    await consumeStream(provider, 'conv-B')
+    expect(captured.map(p => p.metadata?.user_id)).toEqual(['conv-A', 'conv-B'])
+  })
+})