feat(plugin-runtime): add plugin isolation IPC infrastructure

- Protocol layer: Envelope model with Pydantic schema, MsgPack/JSON codecs, unified error codes
- Transport layer: cross-platform IPC abstraction with 4-byte length-prefixed framing (UDS + TCP fallback)
- Host: RPC server, policy engine, circuit breaker, capability service, supervisor with hot-reload
- Runner: RPC client, plugin loader, process entry point
- Tests: 16 passing tests covering protocol, transport, host, and E2E handshake

src/plugin_runtime/transport/factory.py

@@ -0,0 +1,46 @@
+"""传输层工厂
+
+根据运行平台自动选择最优传输实现。
+"""
+
+import sys
+
+from .base import TransportClient, TransportServer
+
+
+def create_transport_server(socket_path: str | None = None) -> TransportServer:
+    """创建传输服务端
+
+    Linux/macOS 使用 UDS，Windows 使用 TCP 回退。
+
+    Args:
+        socket_path: UDS socket 路径（仅 Linux/macOS 有效）
+    """
+    if sys.platform != "win32":
+        from .uds import UDSTransportServer
+        return UDSTransportServer(socket_path=socket_path)
+    else:
+        # Windows 回退到 TCP（后续可改为 Named Pipe）
+        from .tcp import TCPTransportServer
+        return TCPTransportServer()
+
+
+def create_transport_client(address: str) -> TransportClient:
+    """创建传输客户端
+
+    根据地址格式自动判断传输类型：
+    - 包含 '/' 或 '.sock' -> UDS
+    - 包含 ':' -> TCP
+
+    Args:
+        address: Host 端监听地址
+    """
+    if "/" in address or address.endswith(".sock"):
+        from .uds import UDSTransportClient
+        return UDSTransportClient(socket_path=address)
+    elif ":" in address:
+        from .tcp import TCPTransportClient
+        host, port_str = address.rsplit(":", 1)
+        return TCPTransportClient(host=host, port=int(port_str))
+    else:
+        raise ValueError(f"无法识别的传输地址格式: {address}")