feat: 吸收上游 7 个测试文件断言与 placeholder 配置化对齐

上游 ai-kefu → phase1 吸收(Task 11 unit 12):
- 拷入 7 个测试文件,import/夹具按目标库重锚(app.engine.* / conftest
  async_db+build_jiancai_runtime / seed_profiles 提示词锚点)
- 补实现(同步自上游): chat_rest 服务端可信 IP(_server_ip/
  _merge_client_info,直连场景自报假 IP 不再原样落库);widget.js 与
  chat.js 的 data-placeholder 读取(叠加 Task 10 管道:data-* > brand >
  中性兜底,tests/test_placeholder_static.py 守卫)
- 断言重锚以 jc 主线为准: ev.contact_info 存裸号+等待尾注(e164 走
  _cc 派生)、source 值 fallback/customer_stated 口径、推送标注键
  号码补全说明、prompt 静态锚按租户(seed_profiles)双测
- 全量回归 459 passed(基线 421 + 吸收 38)

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

app/engine/routes/chat_rest.py

@@ -33,6 +33,23 @@ class SessionRequest(BaseModel):
     client_info: dict | None = None
 
 
+def _server_ip(request: Request) -> str:
+    """服务端可信 IP：XFF 第一段优先，否则直连 host；全空返回空串。
+
+    同步自上游 ai-kefu(app/api/routes/chat_rest.py)：REST 路径原先只在有
+    XFF 时覆盖自报 ip，直连(无代理)场景自报假 IP 原样落库。"""
+    xff = request.headers.get("x-forwarded-for", "").split(",")[0].strip()
+    return xff or (request.client.host if request.client else "")
+
+
+def _merge_client_info(client_info: dict | None, server_ip: str) -> dict:
+    """服务端 IP 覆盖自报 ip 键；服务端为空时保留自报（空串不得冲掉客户端值）。"""
+    merged = dict(client_info or {})
+    if server_ip:
+        merged["ip"] = server_ip
+    return merged
+
+
 @router.post("/session")
 async def chat_session(req: SessionRequest, request: Request):
     """Resume an active conversation by session_id, or create a new app one.
@@ -41,11 +58,9 @@ async def chat_session(req: SessionRequest, request: Request):
     `raw_info` (only when non-None). `client_info` is stored for analytics only
     (ip/ua/device-id/lang) and never fed to the AI prompt.
     """
-    # 服务端 XFF 优先于客户端自报 ip（客户端自报可伪造，可伪造面最小）
-    xf = request.headers.get("x-forwarded-for", "").split(",")[0].strip()
-    client_info = dict(req.client_info or {})
-    if xf:
-        client_info["ip"] = xf
+    # 服务端可信 IP 同步自上游 ai-kefu：XFF 第一段优先，无 XFF 用直连 host
+    # 覆盖客户端自报（可伪造面最小）；全空保留自报。?site= 处理不变。
+    client_info = _merge_client_info(req.client_info, _server_ip(request))
 
     # Task 10: ?site=<slug> 记入 client_info 作会话站点标(与 WS init 的
     # site 字段同语义)——只加记录,不参与业务逻辑