fix: KB Accelerator tree builder, approve all, canvas delete button

- Fix _build_troubleshooting_tree() to handle deep nesting, warning nodes,
  and DAG deduplication (placed set prevents duplicate IDs)
- Fix step_sync VARCHAR(255) overflow on publish by truncating title
- Add "Approve All" button to KB review screen
- Add delete button (hover-reveal) to flow canvas nodes

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

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

@@ -35,10 +35,11 @@ interface FlowCanvasProps {
   selectedNodeId: string | null
   onNodeSelect: (nodeId: string | null) => void
   onSelectAnswerType: (nodeId: string, type: 'decision' | 'action' | 'solution') => void
+  onNodeDelete?: (nodeId: string) => void
   onNodeContextMenu?: (e: React.MouseEvent, nodeId: string) => void
 }
 
-function FlowCanvasInner({ selectedNodeId, onNodeSelect, onSelectAnswerType, onNodeContextMenu }: FlowCanvasProps) {
+function FlowCanvasInner({ selectedNodeId, onNodeSelect, onSelectAnswerType, onNodeDelete, onNodeContextMenu }: FlowCanvasProps) {
   const { fitView, setCenter } = useReactFlow()
   const { nodes: layoutNodes, edges: layoutEdges, collapsedNodeIds, toggleCollapse, onNodesMeasured } = useTreeLayout(selectedNodeId)
   const [minimapVisible, setMinimapVisible] = useState(true)
@@ -51,7 +52,7 @@ function FlowCanvasInner({ selectedNodeId, onNodeSelect, onSelectAnswerType, onN
         return {
           ...n,
           selected: n.id === selectedNodeId,
-          data: { ...data, onToggleCollapse: toggleCollapse, onContextMenu: onNodeContextMenu },
+          data: { ...data, onToggleCollapse: toggleCollapse, onDelete: onNodeDelete, onContextMenu: onNodeContextMenu },
         }
       }
       if (n.type === 'answerStub') {
@@ -64,7 +65,7 @@ function FlowCanvasInner({ selectedNodeId, onNodeSelect, onSelectAnswerType, onN
       }
       return n
     })
-  }, [layoutNodes, selectedNodeId, toggleCollapse, onSelectAnswerType, onNodeContextMenu])
+  }, [layoutNodes, selectedNodeId, toggleCollapse, onSelectAnswerType, onNodeDelete, onNodeContextMenu])
 
   const [nodes, setNodes, onNodesChange] = useNodesState(nodesWithCallbacks)
   const [edges, setEdges, onEdgesChange] = useEdgesState(layoutEdges)

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

@@ -1,6 +1,6 @@
 import { memo } from 'react'
 import { Handle, Position, type NodeProps } from '@xyflow/react'
-import { HelpCircle, Zap, CheckCircle, ChevronDown, ChevronRight, AlertCircle } from 'lucide-react'
+import { HelpCircle, Zap, CheckCircle, ChevronDown, ChevronRight, AlertCircle, Trash2 } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import type { TreeStructure, NodeType } from '@/types'
 
@@ -40,14 +40,16 @@ export interface FlowCanvasNodeData {
   isCollapsed: boolean
   hasValidationErrors: boolean
   isNew: boolean
+  isRoot: boolean
   onToggleCollapse: (nodeId: string) => void
+  onDelete?: (nodeId: string) => void
   onContextMenu?: (e: React.MouseEvent, nodeId: string) => void
   onAcceptSuggestion?: (nodeId: string) => void
   onDismissSuggestion?: (nodeId: string) => void
 }
 
 function FlowCanvasNodeComponent({ data, selected }: NodeProps) {
-  const { node, hasChildren, isCollapsed, hasValidationErrors, isNew, onToggleCollapse, onContextMenu, onAcceptSuggestion, onDismissSuggestion } = data as unknown as FlowCanvasNodeData
+  const { node, hasChildren, isCollapsed, hasValidationErrors, isNew, isRoot, onToggleCollapse, onDelete, onContextMenu, onAcceptSuggestion, onDismissSuggestion } = data as unknown as FlowCanvasNodeData
   const isGhost = !!(node as unknown as Record<string, unknown>)._suggestion
   const nodeType = node.type as Exclude<NodeType, 'answer'>
   const config = NODE_TYPE_CONFIG[nodeType] ?? NODE_TYPE_CONFIG.decision
@@ -67,7 +69,7 @@ function FlowCanvasNodeComponent({ data, selected }: NodeProps) {
       <div
         onContextMenu={(e) => onContextMenu?.(e, node.id)}
         className={cn(
-          'w-[280px] rounded-xl border border-border bg-card shadow-xs cursor-pointer transition-all',
+          'group w-[280px] rounded-xl border border-border bg-card shadow-xs cursor-pointer transition-all',
           config.borderClass,
           selected && 'ring-1 ring-primary shadow-md',
           isGhost && 'border-dashed border-primary/40! opacity-60'
@@ -94,6 +96,21 @@ function FlowCanvasNodeComponent({ data, selected }: NodeProps) {
           {hasValidationErrors && (
             <AlertCircle className="h-3.5 w-3.5 shrink-0 text-red-400" />
           )}
+
+          {/* Delete button — visible on hover, hidden for root */}
+          {!isRoot && !isGhost && onDelete && (
+            <button
+              type="button"
+              onClick={(e) => {
+                e.stopPropagation()
+                onDelete(node.id)
+              }}
+              className="shrink-0 rounded-md p-1 text-muted-foreground opacity-0 group-hover:opacity-100 hover:bg-red-500/20 hover:text-red-400 transition-all"
+              title="Delete node"
+            >
+              <Trash2 className="h-3.5 w-3.5" />
+            </button>
+          )}
         </div>
 
         {/* Decision options preview */}

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

@@ -19,6 +19,7 @@ interface TreeEditorLayoutProps {
   editingNodeId: string | null
   onNodeSelect: (nodeId: string | null) => void
   onSelectAnswerType: (nodeId: string, type: 'decision' | 'action' | 'solution') => void
+  onNodeDelete?: (nodeId: string) => void
   onNodeContextMenu?: (e: React.MouseEvent, nodeId: string) => void
 }
 
@@ -29,6 +30,7 @@ export function TreeEditorLayout({
   editingNodeId,
   onNodeSelect,
   onSelectAnswerType,
+  onNodeDelete,
   onNodeContextMenu,
 }: TreeEditorLayoutProps) {
   const editorMode = useTreeEditorStore(s => s.editorMode)
@@ -72,6 +74,7 @@ export function TreeEditorLayout({
               selectedNodeId={editingNodeId}
               onNodeSelect={onNodeSelect}
               onSelectAnswerType={onSelectAnswerType}
+              onNodeDelete={onNodeDelete}
               onNodeContextMenu={onNodeContextMenu}
             />
           </div>

frontend/src/components/tree-editor/useTreeLayout.ts

@@ -190,6 +190,7 @@ export function useTreeLayout(selectedNodeId?: string | null): UseTreeLayoutResu
             isCollapsed,
             hasValidationErrors: hasErrors,
             isNew: false,
+            isRoot: node.id === treeStructure?.id,
             onToggleCollapse: () => {}, // placeholder — set by FlowCanvas
           } satisfies FlowCanvasNodeData,
           style: { width: NODE_WIDTH },