fix(canvas): 云端 Agent - 参数错误有限重试并折叠中间失败

backend/internal/app/cloud_agent_approval_preview.go

@@ -66,7 +66,7 @@ func prepareCloudAgentCanvasMutation(repo *repository.Repository, userID, canvas
 	}
 	beforeHash := cloudAgentCanvasHash(doc)
 	if beforeHash != args.SnapshotHash {
-		return nil, creationConflict("画布已变化，本次未写入；请重新读取并重新申请审批")
+		return nil, &cloudAgentFieldArgumentError{error: &cloudAgentArgumentError{creationConflict("画布已变化，本次未写入；请重新读取并重新申请审批")}, Field: "snapshotHash", Issue: "stale_snapshot"}
 	}
 	items, err := applyCloudAgentCanvasPlan(doc, args.Ops)
 	if err != nil {
@@ -86,7 +86,7 @@ func applyCloudAgentCanvasPlan(doc map[string]any, ops []agentCanvasOp) ([]cloud
 	nodes := creationMaps(doc["nodes"])
 	edges := creationMaps(doc["connections"])
 	items := make([]cloudAgentApprovalPreviewItem, 0, len(ops))
-	for _, op := range ops {
+	for opIndex, op := range ops {
 		title, content := "", ""
 		if op.Title != nil {
 			title = *op.Title
@@ -133,7 +133,7 @@ func applyCloudAgentCanvasPlan(doc map[string]any, ops []agentCanvasOp) ([]cloud
 				return nil, BadAuthRequest("连线端点不存在或指向自身")
 			}
 			if err := validateCloudAgentConnection(nodes, op.FromNodeID, op.ToNodeID, edges); err != nil {
-				return nil, err
+				return nil, cloudAgentFieldError(fmt.Sprintf("ops[%d]", opIndex), "invalid_connection", cloudAgentSafeToolError(err))
 			}
 			for _, edge := range edges {
 				if stringValue(edge["id"]) == op.ID || (stringValue(edge["fromNodeId"]) == op.FromNodeID && stringValue(edge["toNodeId"]) == op.ToNodeID) {