Feat: A pipeline's child node can only have one node #9869 (#10695)

### What problem does this PR solve?

Feat: A pipeline's child node can only have one node #9869
### Type of change


- [x] New Feature (non-breaking change which adds functionality)

web/src/locales/en.ts

@@ -1533,8 +1533,8 @@ This delimiter is used to split the input text into several text pieces echo of
         'Your users will see this welcome message at the beginning.',
       modeTip: 'The mode defines how the workflow is initiated.',
       mode: 'Mode',
-      conversational: 'conversational',
+      conversational: 'Conversational',
-      task: 'task',
+      task: 'Task',
       beginInputTip:
         'By defining input parameters, this content can be accessed by other components in subsequent processes.',
       query: 'Query variables',

web/src/pages/agent/canvas/node/handle.tsx

@@ -5,6 +5,8 @@ import { Plus } from 'lucide-react';
 import { useMemo } from 'react';
 import { NodeHandleId } from '../../constant';
 import { HandleContext } from '../../context';
+import { useIsPipeline } from '../../hooks/use-is-pipeline';
+import useGraphStore from '../../store';
 import { useDropdownManager } from '../context';
 import { NextStepDropdown } from './dropdown/next-step-dropdown';
 
@@ -14,9 +16,12 @@ export function CommonHandle({
   ...props
 }: HandleProps & { nodeId: string }) {
   const { visible, hideModal, showModal } = useSetModalState();
-
   const { canShowDropdown, setActiveDropdown, clearActiveDropdown } =
     useDropdownManager();
+  const { hasChildNode } = useGraphStore((state) => state);
+  const isPipeline = useIsPipeline();
+
+  const isConnectable = !(isPipeline && hasChildNode(nodeId)); // Using useMemo will cause isConnectable to not be updated when the subsequent connection line is deleted
 
   const value = useMemo(
     () => ({
@@ -33,6 +38,7 @@ export function CommonHandle({
     <HandleContext.Provider value={value}>
       <Handle
         {...props}
+        isConnectable={isConnectable}
         className={cn(
           'inline-flex justify-center items-center !bg-accent-primary !border-none group-hover:!size-4 group-hover:!rounded-sm',
           className,
@@ -40,6 +46,10 @@ export function CommonHandle({
         onClick={(e) => {
           e.stopPropagation();
 
+          if (!isConnectable) {
+            return;
+          }
+
           if (!canShowDropdown()) {
             return;
           }

web/src/pages/agent/store.ts

@@ -89,6 +89,7 @@ export type RFState = {
   ) => void; // Deleting a condition of a classification operator will delete the related edge
   findAgentToolNodeById: (id: string | null) => string | undefined;
   selectNodeIds: (nodeIds: string[]) => void;
+  hasChildNode: (nodeId: string) => boolean;
 };
 
 // this is our useStore hook that we can use in our components to get parts of the store and call actions
@@ -527,6 +528,10 @@ const useGraphStore = create<RFState>()(
           })),
         );
       },
+      hasChildNode: (nodeId) => {
+        const { edges } = get();
+        return edges.some((edge) => edge.source === nodeId);
+      },
     })),
     { name: 'graph', trace: true },
   ),