feat: auto-create answer stubs on decision save, render AnswerStubCard

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/tree-editor/TreeCanvas.tsx

@@ -2,6 +2,7 @@ import { useState, useCallback, useRef, useEffect } from 'react'
 import { HelpCircle, Zap, CheckCircle, Plus, X } from 'lucide-react'
 import { useTreeEditorStore, findNodeInTree } from '@/store/treeEditorStore'
 import { TreeCanvasNode } from './TreeCanvasNode'
+import { AnswerStubCard } from './AnswerStubCard'
 import type { TreeStructure, NodeType } from '@/types'
 import { cn } from '@/lib/utils'
 
@@ -203,6 +204,28 @@ export function TreeCanvas() {
     (nodeId: string, updates: Partial<TreeStructure>) => {
       updateNode(nodeId, updates)
 
+      // For decision nodes: create answer stubs for any option without a next_node_id
+      if (updates.options) {
+        const options = updates.options
+        const stubsToCreate: Array<{ opt: typeof options[number]; stubId: string }> = []
+
+        options.forEach((opt) => {
+          if (!opt.next_node_id && opt.label.trim()) {
+            const stubId = addNode(nodeId, 'answer')
+            updateNode(stubId, { title: opt.label })
+            stubsToCreate.push({ opt, stubId })
+          }
+        })
+
+        if (stubsToCreate.length > 0) {
+          const updatedOptions = options.map((o) => {
+            const stub = stubsToCreate.find((s) => s.opt.id === o.id)
+            return stub ? { ...o, next_node_id: stub.stubId } : o
+          })
+          updateNode(nodeId, { options: updatedOptions })
+        }
+      }
+
       // Resolve pending link for new nodes
       const link = pendingLinks.get(nodeId)
       if (link) {
@@ -278,6 +301,16 @@ export function TreeCanvas() {
     [duplicateNode]
   )
 
+  // ── Convert answer stub to a real node type ──
+  const handleSelectAnswerType = useCallback(
+    (nodeId: string, type: 'decision' | 'action' | 'solution') => {
+      updateNode(nodeId, { type })
+      setExpandedNodeId(nodeId)
+      selectNode(nodeId)
+    },
+    [updateNode, selectNode]
+  )
+
   // ── Add node flow ──
   const handleAddNodeSelect = useCallback(
     (type: NodeType, parentId: string, optionId?: string) => {
@@ -464,22 +497,30 @@ export function TreeCanvas() {
             </div>
           )}
 
-          {/* The node card itself */}
-          <TreeCanvasNode
-            node={node}
-            depth={0}
-            fromOption={optionLabel}
-            isExpanded={isExpanded}
-            isNew={isNew}
-            onToggleExpand={() => handleToggleExpand(node.id)}
-            onSave={handleSave}
-            onCancelNew={handleCancelNew}
-            onDelete={handleDelete}
-            onDuplicate={handleDuplicate}
-            onDragStart={handleDragStart}
-            onDragOver={(e) => handleDragOver(e, parentId, index)}
-            onDrop={(e) => handleDrop(e, parentId, index)}
-          />
+          {/* The node card — answer stubs get their own component */}
+          {node.type === 'answer' ? (
+            <AnswerStubCard
+              node={node}
+              fromOption={optionLabel}
+              onSelectType={handleSelectAnswerType}
+            />
+          ) : (
+            <TreeCanvasNode
+              node={node}
+              depth={0}
+              fromOption={optionLabel}
+              isExpanded={isExpanded}
+              isNew={isNew}
+              onToggleExpand={() => handleToggleExpand(node.id)}
+              onSave={handleSave}
+              onCancelNew={handleCancelNew}
+              onDelete={handleDelete}
+              onDuplicate={handleDuplicate}
+              onDragStart={handleDragStart}
+              onDragOver={(e) => handleDragOver(e, parentId, index)}
+              onDrop={(e) => handleDrop(e, parentId, index)}
+            />
+          )}
 
           {/* Unlinked option add buttons (decision nodes with unlinked options) */}
           {!isExpanded && unlinkedOptions.length > 0 && (
@@ -586,6 +627,7 @@ export function TreeCanvas() {
       handleCancelNew,
       handleDelete,
       handleDuplicate,
+      handleSelectAnswerType,
       handleDragStart,
       handleDragOver,
       handleDrop,