diff --git a/README.md b/README.md
index b33396e..af686f9 100644
--- a/README.md
+++ b/README.md
@@ -48,6 +48,7 @@
 - 可在 `gateway.token` 配置网关注册令牌；子节点注册/续租需带 `Authorization: Bearer <token>`
 - 可在 `NodeInfo` 中配置 `token`，relay 会自动附加 `Authorization: Bearer <token>`
 - `nodes` 工具支持设备快捷参数：`facing`、`duration_ms`、`command`
+- 设备动作响应统一：`ok/code/error/payload`（code 示例：`ok` `unsupported_action` `transport_error`）
 
 实现位置：
 - `pkg/nodes/types.go`
diff --git a/README_EN.md b/README_EN.md
index ec29f44..88eeea5 100644
--- a/README_EN.md
+++ b/README_EN.md
@@ -48,6 +48,7 @@ A `nodes` tool control-plane PoC is now available:
 - configure `gateway.token` as registration token; child nodes must send `Authorization: Bearer <token>` for register/heartbeat
 - `NodeInfo.token` is supported; relay automatically sets `Authorization: Bearer <token>`
 - `nodes` tool supports device shortcuts: `facing`, `duration_ms`, `command`
+- unified device response envelope: `ok/code/error/payload` (code examples: `ok`, `unsupported_action`, `transport_error`)
 
 Implementation:
 - `pkg/nodes/types.go`
diff --git a/pkg/agent/loop.go b/pkg/agent/loop.go
index c5d5171..322626f 100644
--- a/pkg/agent/loop.go
+++ b/pkg/agent/loop.go
@@ -82,7 +82,7 @@ func NewAgentLoop(cfg *config.Config, msgBus *bus.MessageBus, provider providers
 	nodesManager.RegisterHandler("local", func(req nodes.Request) nodes.Response {
 		switch req.Action {
 		case "run":
-			payload := map[string]interface{}{"transport": "relay-local"}
+			payload := map[string]interface{}{"transport": "relay-local", "simulated": true}
 			if cmdRaw, ok := req.Args["command"].([]interface{}); ok && len(cmdRaw) > 0 {
 				parts := make([]string, 0, len(cmdRaw))
 				for _, x := range cmdRaw {
@@ -90,11 +90,23 @@ func NewAgentLoop(cfg *config.Config, msgBus *bus.MessageBus, provider providers
 				}
 				payload["command"] = parts
 			}
-			return nodes.Response{OK: true, Node: "local", Action: req.Action, Payload: payload}
-		case "camera_snap", "camera_clip", "screen_record", "screen_snapshot", "location_get", "canvas_snapshot", "canvas_action":
-			return nodes.Response{OK: true, Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "simulated": true, "args": req.Args}}
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: payload}
+		case "camera_snap":
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "media_type": "image", "facing": req.Args["facing"], "simulated": true}}
+		case "camera_clip":
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "media_type": "video", "duration_ms": req.Args["duration_ms"], "simulated": true}}
+		case "screen_snapshot":
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "media_type": "image", "simulated": true}}
+		case "screen_record":
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "media_type": "video", "duration_ms": req.Args["duration_ms"], "simulated": true}}
+		case "location_get":
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "lat": 0.0, "lng": 0.0, "accuracy": "simulated"}}
+		case "canvas_snapshot":
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "image": "data:image/png;base64,<simulated>", "simulated": true}}
+		case "canvas_action":
+			return nodes.Response{OK: true, Code: "ok", Node: "local", Action: req.Action, Payload: map[string]interface{}{"transport": "relay-local", "applied": true, "simulated": true, "args": req.Args}}
 		default:
-			return nodes.Response{OK: true, Node: "local", Action: req.Action, Payload: map[string]interface{}{"echo": req.Args, "transport": "relay-local"}}
+			return nodes.Response{OK: false, Code: "unsupported_action", Node: "local", Action: req.Action, Error: "unsupported local simulated action"}
 		}
 	})
 	nodesRouter := &nodes.Router{P2P: &nodes.StubP2PTransport{}, Relay: &nodes.HTTPRelayTransport{Manager: nodesManager}}
diff --git a/pkg/nodes/transport.go b/pkg/nodes/transport.go
index 21e338d..8fe0ba0 100644
--- a/pkg/nodes/transport.go
+++ b/pkg/nodes/transport.go
@@ -96,18 +96,18 @@ func actionHTTPPath(action string) string {
 
 func (s *HTTPRelayTransport) Send(ctx context.Context, req Request) (Response, error) {
 	if s.Manager == nil {
-		return Response{OK: false, Node: req.Node, Action: req.Action, Error: "relay manager not configured"}, nil
+		return Response{OK: false, Code: "relay_unavailable", Node: req.Node, Action: req.Action, Error: "relay manager not configured"}, nil
 	}
 	if resp, ok := s.Manager.Invoke(req); ok {
 		return resp, nil
 	}
 	n, ok := s.Manager.Get(req.Node)
 	if !ok {
-		return Response{OK: false, Node: req.Node, Action: req.Action, Error: "node not found"}, nil
+		return Response{OK: false, Code: "node_not_found", Node: req.Node, Action: req.Action, Error: "node not found"}, nil
 	}
 	endpoint := strings.TrimRight(strings.TrimSpace(n.Endpoint), "/")
 	if endpoint == "" {
-		return Response{OK: false, Node: req.Node, Action: req.Action, Error: "node endpoint not configured"}, nil
+		return Response{OK: false, Code: "endpoint_missing", Node: req.Node, Action: req.Action, Error: "node endpoint not configured"}, nil
 	}
 	client := s.Client
 	if client == nil {
@@ -125,13 +125,13 @@ func (s *HTTPRelayTransport) Send(ctx context.Context, req Request) (Response, e
 	}
 	hresp, err := client.Do(hreq)
 	if err != nil {
-		return Response{OK: false, Node: req.Node, Action: req.Action, Error: err.Error()}, nil
+		return Response{OK: false, Code: "transport_error", Node: req.Node, Action: req.Action, Error: err.Error()}, nil
 	}
 	defer hresp.Body.Close()
 	payload, _ := io.ReadAll(io.LimitReader(hresp.Body, 1<<20))
 	var resp Response
 	if err := json.Unmarshal(payload, &resp); err != nil {
-		return Response{OK: false, Node: req.Node, Action: req.Action, Error: fmt.Sprintf("invalid node response: %s", strings.TrimSpace(string(payload)))}, nil
+		return Response{OK: false, Code: "invalid_response", Node: req.Node, Action: req.Action, Error: fmt.Sprintf("invalid node response: %s", strings.TrimSpace(string(payload)))}, nil
 	}
 	if strings.TrimSpace(resp.Node) == "" {
 		resp.Node = req.Node
@@ -139,5 +139,12 @@ func (s *HTTPRelayTransport) Send(ctx context.Context, req Request) (Response, e
 	if strings.TrimSpace(resp.Action) == "" {
 		resp.Action = req.Action
 	}
+	if strings.TrimSpace(resp.Code) == "" {
+		if resp.OK {
+			resp.Code = "ok"
+		} else {
+			resp.Code = "remote_error"
+		}
+	}
 	return resp, nil
 }
diff --git a/pkg/nodes/types.go b/pkg/nodes/types.go
index 0a9ba24..20611e2 100644
--- a/pkg/nodes/types.go
+++ b/pkg/nodes/types.go
@@ -36,6 +36,7 @@ type Request struct {
 // Envelope for node responses.
 type Response struct {
 	OK      bool                   `json:"ok"`
+	Code    string                 `json:"code,omitempty"`
 	Error   string                 `json:"error,omitempty"`
 	Node    string                 `json:"node,omitempty"`
 	Action  string                 `json:"action,omitempty"`