feat: add AI chat builder frontend — types, API client, store, components, page, routing

- TypeScript types for chat session, messages, and responses
- API client module with all 6 endpoints
- Zustand store with session management, message sending, tree generation, import, resume
- 7 chat components: ChatMessage, ChatInput, ChatPanel, PhaseIndicator, ChatToolbar, EmptyPreview, StaticTreePreview
- AIChatBuilderPage with split-panel layout (60% chat / 40% preview)
- Route at /ai/chat with lazy loading
- "Build with AI" button on TreeLibraryPage
- Session resume via URL search params

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

frontend/src/api/aiChat.ts

@@ -0,0 +1,44 @@
+import { apiClient } from './client'
+import type {
+  AIChatStartResponse,
+  AIChatMessageResponse,
+  AIChatSessionResponse,
+  AIChatGenerateResponse,
+  AIChatImportResponse,
+} from '@/types'
+
+export const aiChatApi = {
+  startSession: async (flowType: 'troubleshooting' | 'procedural'): Promise<AIChatStartResponse> => {
+    const { data } = await apiClient.post('/ai/chat/sessions', { flow_type: flowType })
+    return data
+  },
+
+  sendMessage: async (sessionId: string, content: string): Promise<AIChatMessageResponse> => {
+    const { data } = await apiClient.post(`/ai/chat/sessions/${sessionId}/messages`, { content })
+    return data
+  },
+
+  getSession: async (sessionId: string): Promise<AIChatSessionResponse> => {
+    const { data } = await apiClient.get(`/ai/chat/sessions/${sessionId}`)
+    return data
+  },
+
+  generateTree: async (sessionId: string): Promise<AIChatGenerateResponse> => {
+    const { data } = await apiClient.post(`/ai/chat/sessions/${sessionId}/generate`)
+    return data
+  },
+
+  importTree: async (
+    sessionId: string,
+    params?: { name?: string; description?: string; category_id?: string; tags?: string[] }
+  ): Promise<AIChatImportResponse> => {
+    const { data } = await apiClient.post(`/ai/chat/sessions/${sessionId}/import`, params || {})
+    return data
+  },
+
+  abandonSession: async (sessionId: string): Promise<void> => {
+    await apiClient.delete(`/ai/chat/sessions/${sessionId}`)
+  },
+}
+
+export default aiChatApi

frontend/src/api/index.ts

@@ -17,3 +17,4 @@ export { targetListsApi } from './targetLists'
 export { maintenanceSchedulesApi, batchLaunchApi } from './maintenanceSchedules'
 export { default as feedbackApi } from './feedback'
 export { default as aiBuilderApi } from './aiBuilder'
+export { default as aiChatApi } from './aiChat'

frontend/src/components/ai-chat/ChatInput.tsx

@@ -0,0 +1,72 @@
+import { useState, useRef, useCallback } from 'react'
+import { Send } from 'lucide-react'
+import { cn } from '@/lib/utils'
+
+interface ChatInputProps {
+  onSend: (content: string) => void
+  disabled?: boolean
+  placeholder?: string
+}
+
+export function ChatInput({ onSend, disabled, placeholder = 'Type a message...' }: ChatInputProps) {
+  const [value, setValue] = useState('')
+  const textareaRef = useRef<HTMLTextAreaElement>(null)
+
+  const handleSend = useCallback(() => {
+    const trimmed = value.trim()
+    if (!trimmed || disabled) return
+    onSend(trimmed)
+    setValue('')
+    if (textareaRef.current) {
+      textareaRef.current.style.height = 'auto'
+    }
+  }, [value, disabled, onSend])
+
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    if (e.key === 'Enter' && !e.shiftKey) {
+      e.preventDefault()
+      handleSend()
+    }
+  }
+
+  const handleInput = () => {
+    if (textareaRef.current) {
+      textareaRef.current.style.height = 'auto'
+      textareaRef.current.style.height = Math.min(textareaRef.current.scrollHeight, 160) + 'px'
+    }
+  }
+
+  return (
+    <div className="flex items-end gap-2 border-t border-border bg-card px-4 py-3">
+      <textarea
+        ref={textareaRef}
+        value={value}
+        onChange={(e) => setValue(e.target.value)}
+        onKeyDown={handleKeyDown}
+        onInput={handleInput}
+        placeholder={placeholder}
+        disabled={disabled}
+        rows={1}
+        className={cn(
+          'flex-1 resize-none rounded-lg border border-border bg-background px-3 py-2',
+          'text-sm text-foreground placeholder:text-muted-foreground',
+          'focus:border-primary focus:ring-1 focus:ring-primary/20 focus:outline-none',
+          'disabled:opacity-50 disabled:cursor-not-allowed',
+          'max-h-40'
+        )}
+      />
+      <button
+        onClick={handleSend}
+        disabled={disabled || !value.trim()}
+        className={cn(
+          'flex h-10 w-10 shrink-0 items-center justify-center rounded-lg',
+          'bg-gradient-brand text-white shadow-lg shadow-primary/20',
+          'hover:opacity-90 transition-opacity',
+          'disabled:opacity-50 disabled:cursor-not-allowed'
+        )}
+      >
+        <Send className="h-4 w-4" />
+      </button>
+    </div>
+  )
+}

frontend/src/components/ai-chat/ChatMessage.tsx

@@ -0,0 +1,41 @@
+import { Bot, User } from 'lucide-react'
+import { MarkdownContent } from '@/components/ui/MarkdownContent'
+import { cn } from '@/lib/utils'
+import type { ChatMessage as ChatMessageType } from '@/types'
+
+interface ChatMessageProps {
+  message: ChatMessageType
+}
+
+export function ChatMessage({ message }: ChatMessageProps) {
+  const isAI = message.role === 'assistant'
+
+  return (
+    <div className={cn('flex gap-3', isAI ? 'items-start' : 'items-start justify-end')}>
+      {isAI && (
+        <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-lg bg-primary/10">
+          <Bot className="h-4 w-4 text-primary" />
+        </div>
+      )}
+      <div
+        className={cn(
+          'max-w-[85%] rounded-xl px-4 py-3',
+          isAI
+            ? 'bg-card border border-border'
+            : 'bg-primary/10 border border-primary/20'
+        )}
+      >
+        {isAI ? (
+          <MarkdownContent content={message.content} className="text-sm" />
+        ) : (
+          <p className="text-sm text-foreground whitespace-pre-wrap">{message.content}</p>
+        )}
+      </div>
+      {!isAI && (
+        <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-lg bg-accent">
+          <User className="h-4 w-4 text-foreground" />
+        </div>
+      )}
+    </div>
+  )
+}

frontend/src/components/ai-chat/ChatPanel.tsx

@@ -0,0 +1,47 @@
+import { useEffect, useRef } from 'react'
+import { ChatMessage } from './ChatMessage'
+import { ChatInput } from './ChatInput'
+import { Spinner } from '@/components/common/Spinner'
+import type { ChatMessage as ChatMessageType } from '@/types'
+
+interface ChatPanelProps {
+  messages: ChatMessageType[]
+  isResponding: boolean
+  onSendMessage: (content: string) => void
+  disabled?: boolean
+}
+
+export function ChatPanel({ messages, isResponding, onSendMessage, disabled }: ChatPanelProps) {
+  const scrollRef = useRef<HTMLDivElement>(null)
+
+  // Auto-scroll to bottom on new messages
+  useEffect(() => {
+    if (scrollRef.current) {
+      scrollRef.current.scrollTop = scrollRef.current.scrollHeight
+    }
+  }, [messages, isResponding])
+
+  return (
+    <div className="flex h-full flex-col">
+      {/* Messages */}
+      <div ref={scrollRef} className="flex-1 overflow-y-auto px-4 py-4 space-y-4">
+        {messages.map((msg, i) => (
+          <ChatMessage key={i} message={msg} />
+        ))}
+        {isResponding && (
+          <div className="flex items-center gap-2 text-sm text-muted-foreground">
+            <Spinner size="sm" />
+            <span>Thinking...</span>
+          </div>
+        )}
+      </div>
+
+      {/* Input */}
+      <ChatInput
+        onSend={onSendMessage}
+        disabled={disabled || isResponding}
+        placeholder={isResponding ? 'Waiting for response...' : 'Type a message...'}
+      />
+    </div>
+  )
+}

frontend/src/components/ai-chat/ChatToolbar.tsx

@@ -0,0 +1,76 @@
+import { Sparkles, Download, RotateCcw, ArrowRight } from 'lucide-react'
+import { PhaseIndicator } from './PhaseIndicator'
+import { cn } from '@/lib/utils'
+import type { InterviewPhase } from '@/types'
+
+interface ChatToolbarProps {
+  currentPhase: InterviewPhase
+  status: 'idle' | 'active' | 'completed' | 'abandoned'
+  isGenerating: boolean
+  hasGeneratedTree: boolean
+  onGenerate: () => void
+  onImport: () => void
+  onReset: () => void
+}
+
+export function ChatToolbar({
+  currentPhase,
+  status,
+  isGenerating,
+  hasGeneratedTree,
+  onGenerate,
+  onImport,
+  onReset,
+}: ChatToolbarProps) {
+  return (
+    <div className="flex items-center justify-between border-b border-border bg-card px-4 py-2">
+      <div className="flex items-center gap-3">
+        <div className="flex items-center gap-2 text-sm font-medium text-foreground">
+          <Sparkles className="h-4 w-4 text-primary" />
+          Build with AI
+        </div>
+        <PhaseIndicator currentPhase={currentPhase} />
+      </div>
+
+      <div className="flex items-center gap-2">
+        {status === 'active' && !hasGeneratedTree && (
+          <button
+            onClick={onGenerate}
+            disabled={isGenerating}
+            className={cn(
+              'flex items-center gap-1.5 rounded-lg px-3 py-1.5 text-sm font-medium',
+              'bg-gradient-brand text-white shadow-lg shadow-primary/20',
+              'hover:opacity-90 transition-opacity',
+              'disabled:opacity-50 disabled:cursor-not-allowed'
+            )}
+          >
+            <Download className="h-3.5 w-3.5" />
+            {isGenerating ? 'Generating...' : 'Generate Flow'}
+          </button>
+        )}
+
+        {hasGeneratedTree && (
+          <button
+            onClick={onImport}
+            className={cn(
+              'flex items-center gap-1.5 rounded-lg px-3 py-1.5 text-sm font-medium',
+              'bg-gradient-brand text-white shadow-lg shadow-primary/20',
+              'hover:opacity-90 transition-opacity'
+            )}
+          >
+            <ArrowRight className="h-3.5 w-3.5" />
+            Import to Editor
+          </button>
+        )}
+
+        <button
+          onClick={onReset}
+          className="flex items-center gap-1.5 rounded-lg border border-border px-3 py-1.5 text-sm text-muted-foreground hover:bg-accent hover:text-foreground transition-colors"
+        >
+          <RotateCcw className="h-3.5 w-3.5" />
+          Start Over
+        </button>
+      </div>
+    </div>
+  )
+}

frontend/src/components/ai-chat/EmptyPreview.tsx

@@ -0,0 +1,13 @@
+import { TreeDeciduous } from 'lucide-react'
+
+export function EmptyPreview() {
+  return (
+    <div className="flex h-full flex-col items-center justify-center p-8 text-center">
+      <TreeDeciduous className="h-12 w-12 text-muted-foreground/30 mb-4" />
+      <h3 className="text-sm font-medium text-muted-foreground mb-1">Flow Preview</h3>
+      <p className="text-xs text-muted-foreground/70 max-w-48">
+        Your flow will appear here as you describe it to the AI
+      </p>
+    </div>
+  )
+}

frontend/src/components/ai-chat/PhaseIndicator.tsx

@@ -0,0 +1,50 @@
+import { cn } from '@/lib/utils'
+import type { InterviewPhase } from '@/types'
+
+const PHASES: { key: InterviewPhase; label: string }[] = [
+  { key: 'scoping', label: 'Scoping' },
+  { key: 'discovery', label: 'Discovery' },
+  { key: 'enrichment', label: 'Enrichment' },
+  { key: 'review', label: 'Review' },
+  { key: 'generation', label: 'Generate' },
+]
+
+interface PhaseIndicatorProps {
+  currentPhase: InterviewPhase
+}
+
+export function PhaseIndicator({ currentPhase }: PhaseIndicatorProps) {
+  const currentIndex = PHASES.findIndex((p) => p.key === currentPhase)
+
+  return (
+    <div className="flex items-center gap-1">
+      {PHASES.map((phase, i) => {
+        const isActive = phase.key === currentPhase
+        const isCompleted = i < currentIndex
+
+        return (
+          <div key={phase.key} className="flex items-center">
+            {i > 0 && (
+              <div
+                className={cn(
+                  'mx-1 h-px w-4',
+                  isCompleted ? 'bg-primary' : 'bg-border'
+                )}
+              />
+            )}
+            <span
+              className={cn(
+                'font-label text-[0.6875rem] uppercase tracking-wide px-2 py-0.5 rounded',
+                isActive && 'text-primary bg-primary/10 font-medium',
+                isCompleted && 'text-primary',
+                !isActive && !isCompleted && 'text-muted-foreground'
+              )}
+            >
+              {phase.label}
+            </span>
+          </div>
+        )
+      })}
+    </div>
+  )
+}

frontend/src/components/ai-chat/StaticTreePreview.tsx

@@ -0,0 +1,80 @@
+import { useState, useMemo, useCallback } from 'react'
+import { TreePreviewNode } from '@/components/tree-preview/TreePreviewNode'
+import type { SharedLinksMap } from '@/components/tree-preview/TreePreviewPanel'
+import type { TreeStructure } from '@/types'
+
+interface StaticTreePreviewProps {
+  tree: TreeStructure
+  name?: string
+}
+
+function findNodeInTree(nodeId: string, tree: TreeStructure): TreeStructure | null {
+  if (tree.id === nodeId) return tree
+  if (tree.children) {
+    for (const child of tree.children) {
+      const found = findNodeInTree(nodeId, child)
+      if (found) return found
+    }
+  }
+  return null
+}
+
+function buildSharedLinksMap(node: TreeStructure, map: SharedLinksMap = new Map()): SharedLinksMap {
+  const nodeLabel = node.type === 'decision' ? node.question : node.title
+  if (node.type === 'decision' && node.options) {
+    for (const opt of node.options) {
+      if (opt.next_node_id) {
+        const existing = map.get(opt.next_node_id) || []
+        existing.push({ id: node.id, label: nodeLabel || 'Untitled' })
+        map.set(opt.next_node_id, existing)
+      }
+    }
+  }
+  if (node.type === 'action' && node.next_node_id) {
+    const existing = map.get(node.next_node_id) || []
+    existing.push({ id: node.id, label: nodeLabel || 'Untitled' })
+    map.set(node.next_node_id, existing)
+  }
+  if (node.children) {
+    for (const child of node.children) {
+      buildSharedLinksMap(child, map)
+    }
+  }
+  return map
+}
+
+export function StaticTreePreview({ tree, name }: StaticTreePreviewProps) {
+  const [selectedNodeId, setSelectedNodeId] = useState<string | null>(null)
+
+  const findNode = useCallback(
+    (nodeId: string) => findNodeInTree(nodeId, tree),
+    [tree]
+  )
+
+  const sharedLinksMap = useMemo(() => buildSharedLinksMap(tree), [tree])
+
+  return (
+    <div className="flex h-full flex-col">
+      <div className="border-b border-border px-4 py-2">
+        <h3 className="text-sm font-semibold text-foreground">
+          Preview: {name || 'Untitled Flow'}
+        </h3>
+        <p className="text-xs text-muted-foreground">
+          Click a node to select
+        </p>
+      </div>
+      <div className="flex-1 overflow-auto p-4">
+        <div className="inline-block min-w-full">
+          <TreePreviewNode
+            node={tree}
+            selectedNodeId={selectedNodeId}
+            onSelect={setSelectedNodeId}
+            depth={0}
+            findNode={findNode}
+            sharedLinksMap={sharedLinksMap}
+          />
+        </div>
+      </div>
+    </div>
+  )
+}

frontend/src/pages/AIChatBuilderPage.tsx

@@ -0,0 +1,151 @@
+import { useCallback, useEffect } from 'react'
+import { useNavigate, useSearchParams } from 'react-router-dom'
+import { useAIChatStore } from '@/store/aiChatStore'
+import { ChatPanel } from '@/components/ai-chat/ChatPanel'
+import { ChatToolbar } from '@/components/ai-chat/ChatToolbar'
+import { EmptyPreview } from '@/components/ai-chat/EmptyPreview'
+import { StaticTreePreview } from '@/components/ai-chat/StaticTreePreview'
+import { Spinner } from '@/components/common/Spinner'
+import { getTreeEditorPath } from '@/lib/routing'
+import { toast } from '@/lib/toast'
+import type { TreeStructure } from '@/types'
+
+export function AIChatBuilderPage() {
+  const navigate = useNavigate()
+  const [searchParams, setSearchParams] = useSearchParams()
+  const flowType = searchParams.get('type') === 'procedural' ? 'procedural' : 'troubleshooting'
+
+  const {
+    sessionId,
+    status,
+    currentPhase,
+    messages,
+    isResponding,
+    workingTree,
+    treeMetadata,
+    generatedTree,
+    isGenerating,
+    error,
+    startSession,
+    sendMessage,
+    generateTree,
+    importToEditor,
+    abandonSession,
+    resumeSession,
+  } = useAIChatStore()
+
+  // Start or resume session on mount
+  useEffect(() => {
+    const resumeId = searchParams.get('session')
+    if (resumeId && !sessionId) {
+      resumeSession(resumeId)
+    } else if (!sessionId && status === 'idle') {
+      startSession(flowType as 'troubleshooting' | 'procedural')
+    }
+  }, []) // eslint-disable-line react-hooks/exhaustive-deps
+
+  // Store sessionId in URL for resume support
+  useEffect(() => {
+    if (sessionId && !searchParams.get('session')) {
+      setSearchParams((prev) => {
+        const next = new URLSearchParams(prev)
+        next.set('session', sessionId)
+        return next
+      }, { replace: true })
+    }
+  }, [sessionId, searchParams, setSearchParams])
+
+  const handleSendMessage = useCallback(
+    (content: string) => {
+      sendMessage(content)
+    },
+    [sendMessage]
+  )
+
+  const handleGenerate = useCallback(() => {
+    generateTree()
+  }, [generateTree])
+
+  const handleImport = useCallback(async () => {
+    try {
+      const treeId = await importToEditor({
+        name: treeMetadata?.name,
+        description: treeMetadata?.description,
+        tags: treeMetadata?.tags,
+      })
+      const path = getTreeEditorPath(treeId, flowType)
+      navigate(path)
+      toast.success('Flow imported to editor')
+    } catch {
+      toast.error('Failed to import flow')
+    }
+  }, [importToEditor, treeMetadata, flowType, navigate])
+
+  const handleReset = useCallback(() => {
+    abandonSession()
+    // Clear session from URL
+    setSearchParams((prev) => {
+      const next = new URLSearchParams(prev)
+      next.delete('session')
+      return next
+    }, { replace: true })
+    startSession(flowType as 'troubleshooting' | 'procedural')
+  }, [abandonSession, startSession, flowType, setSearchParams])
+
+  // Show error toast
+  useEffect(() => {
+    if (error) {
+      toast.error(error)
+    }
+  }, [error])
+
+  if (status === 'idle' && !sessionId) {
+    return (
+      <div className="flex h-full items-center justify-center">
+        <Spinner />
+      </div>
+    )
+  }
+
+  const previewTree = (generatedTree || workingTree) as TreeStructure | null
+
+  return (
+    <div className="flex h-full flex-col">
+      <ChatToolbar
+        currentPhase={currentPhase}
+        status={status}
+        isGenerating={isGenerating}
+        hasGeneratedTree={!!generatedTree}
+        onGenerate={handleGenerate}
+        onImport={handleImport}
+        onReset={handleReset}
+      />
+
+      <div className="flex flex-1 overflow-hidden">
+        {/* Left panel: Chat (60%) */}
+        <div className="flex w-3/5 flex-col border-r border-border max-lg:w-full">
+          <ChatPanel
+            messages={messages}
+            isResponding={isResponding}
+            onSendMessage={handleSendMessage}
+            disabled={status !== 'active'}
+          />
+        </div>
+
+        {/* Right panel: Tree preview (40%) — hidden below 1024px */}
+        <div className="w-2/5 overflow-hidden bg-background max-lg:hidden">
+          {previewTree ? (
+            <StaticTreePreview
+              tree={previewTree}
+              name={treeMetadata?.name}
+            />
+          ) : (
+            <EmptyPreview />
+          )}
+        </div>
+      </div>
+    </div>
+  )
+}
+
+export default AIChatBuilderPage

frontend/src/pages/TreeLibraryPage.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useState, useCallback, useMemo } from 'react'
 import { useNavigate, useSearchParams } from 'react-router-dom'
-import { X, RotateCcw, Play } from 'lucide-react'
+import { X, RotateCcw, Play, Sparkles } from 'lucide-react'
 import { treesApi } from '@/api/trees'
 import { categoriesApi } from '@/api/categories'
 import { foldersApi } from '@/api/folders'
@@ -272,11 +272,22 @@ export function TreeLibraryPage() {
               </p>
             </div>
             {canCreateTrees && (
-              <CreateFlowDropdown
-                aiEnabled={aiEnabled}
-                onOpenAIBuilder={() => setShowAIBuilder(true)}
-                label="Create New"
-              />
+              <div className="flex items-center gap-2">
+                {aiEnabled && (
+                  <button
+                    onClick={() => navigate('/ai/chat')}
+                    className="flex items-center gap-2 rounded-lg bg-gradient-brand px-4 py-2 text-sm font-medium text-white shadow-lg shadow-primary/20 hover:opacity-90 transition-opacity"
+                  >
+                    <Sparkles className="h-4 w-4" />
+                    Build with AI
+                  </button>
+                )}
+                <CreateFlowDropdown
+                  aiEnabled={aiEnabled}
+                  onOpenAIBuilder={() => setShowAIBuilder(true)}
+                  label="Create New"
+                />
+              </div>
             )}
           </div>
 

frontend/src/router.tsx

@@ -33,6 +33,7 @@ const TeamAnalyticsPage = lazy(() => import('@/pages/TeamAnalyticsPage'))
 const MyAnalyticsPage = lazy(() => import('@/pages/MyAnalyticsPage'))
 const FeedbackPage = lazy(() => import('@/pages/FeedbackPage'))
 const StepLibraryPage = lazy(() => import('@/pages/StepLibraryPage'))
+const AIChatBuilderPage = lazy(() => import('@/pages/AIChatBuilderPage'))
 const AccountSettingsPage = lazy(() => import('@/pages/AccountSettingsPage'))
 // Admin pages
 const AdminLayout = lazy(() => import('@/components/admin/AdminLayout'))
@@ -253,6 +254,14 @@ export const router = createBrowserRouter([
           </Suspense>
         ),
       },
+      {
+        path: 'ai/chat',
+        element: (
+          <Suspense fallback={<PageLoader />}>
+            <AIChatBuilderPage />
+          </Suspense>
+        ),
+      },
       // Admin routes
       {
         path: 'admin',

frontend/src/store/aiChatStore.ts

@@ -0,0 +1,190 @@
+import { create } from 'zustand'
+import { aiChatApi } from '@/api/aiChat'
+import type {
+  ChatMessage,
+  InterviewPhase,
+  TreeStructure,
+} from '@/types'
+
+interface TreeMetadata {
+  name?: string
+  description?: string
+  tags?: string[]
+  category_id?: string
+}
+
+interface AIChatState {
+  // Session
+  sessionId: string | null
+  status: 'idle' | 'active' | 'completed' | 'abandoned'
+  currentPhase: InterviewPhase
+  flowType: 'troubleshooting' | 'procedural' | null
+
+  // Conversation
+  messages: ChatMessage[]
+  isResponding: boolean
+
+  // Progressive tree
+  workingTree: TreeStructure | null
+  treeMetadata: TreeMetadata | null
+
+  // Final generation
+  generatedTree: TreeStructure | null
+  isGenerating: boolean
+  importedTreeId: string | null
+
+  // Error
+  error: string | null
+
+  // Actions
+  startSession: (flowType: 'troubleshooting' | 'procedural') => Promise<void>
+  sendMessage: (content: string) => Promise<void>
+  generateTree: () => Promise<void>
+  importToEditor: (params?: { name?: string; description?: string; category_id?: string; tags?: string[] }) => Promise<string>
+  abandonSession: () => Promise<void>
+  resumeSession: (sessionId: string) => Promise<void>
+  reset: () => void
+}
+
+const initialState = {
+  sessionId: null,
+  status: 'idle' as const,
+  currentPhase: 'scoping' as InterviewPhase,
+  flowType: null,
+  messages: [],
+  isResponding: false,
+  workingTree: null,
+  treeMetadata: null,
+  generatedTree: null,
+  isGenerating: false,
+  importedTreeId: null,
+  error: null,
+}
+
+export const useAIChatStore = create<AIChatState>((set, get) => ({
+  ...initialState,
+
+  startSession: async (flowType) => {
+    set({ ...initialState, status: 'active', flowType, isResponding: true, error: null })
+
+    try {
+      const response = await aiChatApi.startSession(flowType)
+      set({
+        sessionId: response.session_id,
+        currentPhase: response.current_phase,
+        messages: [{
+          role: 'assistant',
+          content: response.greeting,
+          timestamp: new Date().toISOString(),
+        }],
+        isResponding: false,
+      })
+    } catch (e: unknown) {
+      const message = e instanceof Error ? e.message : 'Failed to start session'
+      set({ error: message, isResponding: false, status: 'idle' })
+    }
+  },
+
+  sendMessage: async (content) => {
+    const { sessionId, messages } = get()
+    if (!sessionId) return
+
+    const userMessage: ChatMessage = {
+      role: 'user',
+      content,
+      timestamp: new Date().toISOString(),
+    }
+
+    set({
+      messages: [...messages, userMessage],
+      isResponding: true,
+      error: null,
+    })
+
+    try {
+      const response = await aiChatApi.sendMessage(sessionId, content)
+      const aiMessage: ChatMessage = {
+        role: 'assistant',
+        content: response.content,
+        timestamp: new Date().toISOString(),
+      }
+
+      set((state) => ({
+        messages: [...state.messages, aiMessage],
+        currentPhase: response.current_phase,
+        workingTree: (response.working_tree as TreeStructure | null) ?? state.workingTree,
+        treeMetadata: (response.tree_metadata as TreeMetadata | null) ?? state.treeMetadata,
+        isResponding: false,
+      }))
+    } catch (e: unknown) {
+      const message = e instanceof Error ? e.message : 'Failed to send message'
+      set({ error: message, isResponding: false })
+    }
+  },
+
+  generateTree: async () => {
+    const { sessionId } = get()
+    if (!sessionId) return
+
+    set({ isGenerating: true, error: null })
+
+    try {
+      const response = await aiChatApi.generateTree(sessionId)
+      set({
+        generatedTree: response.tree_structure as unknown as TreeStructure,
+        workingTree: response.tree_structure as unknown as TreeStructure,
+        treeMetadata: response.tree_metadata as TreeMetadata,
+        status: 'completed',
+        isGenerating: false,
+      })
+    } catch (e: unknown) {
+      const message = e instanceof Error ? e.message : 'Failed to generate tree'
+      set({ error: message, isGenerating: false })
+    }
+  },
+
+  importToEditor: async (params) => {
+    const { sessionId } = get()
+    if (!sessionId) throw new Error('No active session')
+
+    const response = await aiChatApi.importTree(sessionId, params)
+    set({ importedTreeId: response.tree_id })
+    return response.tree_id
+  },
+
+  abandonSession: async () => {
+    const { sessionId } = get()
+    if (!sessionId) return
+
+    try {
+      await aiChatApi.abandonSession(sessionId)
+    } catch {
+      // Best effort — session may have already expired
+    }
+    set({ ...initialState })
+  },
+
+  resumeSession: async (sessionId) => {
+    set({ isResponding: true, error: null })
+
+    try {
+      const session = await aiChatApi.getSession(sessionId)
+      set({
+        sessionId: session.session_id,
+        status: session.status === 'active' ? 'active' : (session.status as 'completed' | 'abandoned'),
+        currentPhase: session.current_phase,
+        flowType: session.flow_type,
+        messages: session.conversation_history as ChatMessage[],
+        workingTree: session.working_tree as TreeStructure | null,
+        treeMetadata: session.tree_metadata as TreeMetadata | null,
+        generatedTree: session.generated_tree as TreeStructure | null,
+        isResponding: false,
+      })
+    } catch (e: unknown) {
+      const message = e instanceof Error ? e.message : 'Failed to resume session'
+      set({ error: message, isResponding: false })
+    }
+  },
+
+  reset: () => set({ ...initialState }),
+}))

frontend/src/types/ai-chat.ts

@@ -0,0 +1,43 @@
+export type InterviewPhase = 'scoping' | 'discovery' | 'enrichment' | 'review' | 'generation'
+
+export interface ChatMessage {
+  role: 'user' | 'assistant'
+  content: string
+  timestamp: string
+}
+
+export interface AIChatStartResponse {
+  session_id: string
+  greeting: string
+  current_phase: InterviewPhase
+}
+
+export interface AIChatMessageResponse {
+  content: string
+  current_phase: InterviewPhase
+  working_tree: Record<string, unknown> | null
+  tree_metadata: Record<string, unknown> | null
+}
+
+export interface AIChatSessionResponse {
+  session_id: string
+  status: 'active' | 'completed' | 'abandoned'
+  current_phase: InterviewPhase
+  flow_type: 'troubleshooting' | 'procedural'
+  conversation_history: ChatMessage[]
+  working_tree: Record<string, unknown> | null
+  tree_metadata: Record<string, unknown> | null
+  message_count: number
+  generated_tree: Record<string, unknown> | null
+}
+
+export interface AIChatGenerateResponse {
+  tree_structure: Record<string, unknown>
+  tree_metadata: Record<string, unknown>
+  status: string
+}
+
+export interface AIChatImportResponse {
+  tree_id: string
+  tree_type: string
+}

frontend/src/types/index.ts

@@ -52,3 +52,13 @@ export type {
   AIFixProposal,
   AIFixValidationError,
 } from './ai-fix'
+
+export type {
+  InterviewPhase,
+  ChatMessage,
+  AIChatStartResponse,
+  AIChatMessageResponse,
+  AIChatSessionResponse,
+  AIChatGenerateResponse,
+  AIChatImportResponse,
+} from './ai-chat'