fix(chv): api_client 接受 204 无 Content-Length 响应

WSL 真机实测（CHV 54.0.0）：vm.create 成功回 204 No Content，
且不带 Content-Length、无体；严格校验（P1-6）把合法成功当
失败拒掉，wake_vm 卡在 vm.create。204/304 按 HTTP 语义体长
恒为 0，不要求长度、不读体（keep-alive 下读会等到超时）；
其它状态仍严格（无长度/截断/chunked 均拒绝）。
测试：test_chv_cover100 新增 3 项（204 成功、200 无长度仍拒、
_parse_status）

cloud/tests/test_chv_cover100.py

@@ -103,6 +103,50 @@ class ApiClientCover100Test(unittest.TestCase):
         self.assertIn(b'"name": "vm1"', fake.sent)
         self.assertTrue(fake.closed)
 
+    def test_204_without_content_length_is_success(self):
+        # 真机实测（2026-11-07，CHV 54.0.0）：vm.create 成功回
+        # 204 No Content，且不带 Content-Length、无体——严格
+        # 校验会把合法成功当失败拒掉。204 按 HTTP 语义体长为
+        # 0，不读体（keep-alive 下读会等到超时；假 socket 的
+        # 剩余片为空，读体即报截断，本测试能抓住误读）。
+        fake = _FakeApiSocket([
+            b"HTTP/1.1 204 No Content\r\nServer: Cloud Hypervisor API"
+            b"\r\nConnection: keep-alive\r\n\r\n",
+        ])
+        with tempfile.TemporaryDirectory() as tmp:
+            sock_path = os.path.join(tmp, "chv.sock")
+            with open(sock_path, "w") as fh:
+                fh.write("x")
+            with mock.patch.object(api_client.socket, "socket",
+                                   lambda *a, **k: fake):
+                status, body = api_client._unix_socket_api(
+                    sock_path, "PUT", "/vm.create",
+                    payload={"cpus": {"boot_vcpus": 2}})
+        self.assertEqual(status, 204)
+        self.assertEqual(body, {})
+        self.assertTrue(fake.closed)
+
+    def test_200_without_content_length_still_rejected(self):
+        # 204 例外不得放宽其它状态：200 无长度仍拒绝。
+        fake = _FakeApiSocket([
+            b"HTTP/1.1 200 OK\r\nContent-Type: application/json"
+            b"\r\n\r\n{}",
+        ])
+        with tempfile.TemporaryDirectory() as tmp:
+            sock_path = os.path.join(tmp, "chv.sock")
+            with open(sock_path, "w") as fh:
+                fh.write("x")
+            with mock.patch.object(api_client.socket, "socket",
+                                   lambda *a, **k: fake):
+                with self.assertRaises(RuntimeError):
+                    api_client._unix_socket_api(
+                        sock_path, "GET", "/vmm.ping")
+
+    def test_parse_status(self):
+        self.assertEqual(api_client._parse_status("HTTP/1.1 204 foo"), 204)
+        self.assertEqual(api_client._parse_status("HTTP/1.1 OK"), 0)
+        self.assertEqual(api_client._parse_status(""), 0)
+
     def test_parse_status_non_numeric_is_zero(self):
         status, _body = api_client._parse_response(
             "HTTP/1.1 OK\r\n\r\n", b"{}")