diff --git a/frontend/src/apis/chat/chat.api.ts b/frontend/src/apis/chat/chat.api.ts
new file mode 100644
index 0000000..e039f3c
--- /dev/null
+++ b/frontend/src/apis/chat/chat.api.ts
@@ -0,0 +1,33 @@
+// 채팅 엔드포인트 호출 함수 (순수 HTTP 레이어, React 의존 없음).
+import { http } from '@/apis/http'
+import type {
+  ChatInitResponse,
+  ChatMessagesResponse,
+  ChatSendRequest,
+  ChatSendResponse,
+} from './chat.type'
+
+export const chatApi = {
+  /** GET .../chat/init — 상품·견적 메타 + 세션 상태 + 마감 시각 */
+  getInit: async (sessionId: string): Promise<ChatInitResponse> => {
+    const res = await http.get<ChatInitResponse>(`/v1/negotiation/sessions/${sessionId}/chat/init`)
+    return res.data
+  },
+
+  /** GET .../chat/messages — 대화 히스토리(seq 오름차순). 비어 있으면 오프닝 포함 */
+  getMessages: async (sessionId: string): Promise<ChatMessagesResponse> => {
+    const res = await http.get<ChatMessagesResponse>(
+      `/v1/negotiation/sessions/${sessionId}/chat/messages`,
+    )
+    return res.data
+  },
+
+  /** POST .../chat/send — 한 턴 전송, 새 봇 메시지 1건 반환(append-only) */
+  send: async (sessionId: string, body: ChatSendRequest): Promise<ChatSendResponse> => {
+    const res = await http.post<ChatSendResponse>(
+      `/v1/negotiation/sessions/${sessionId}/chat/send`,
+      body,
+    )
+    return res.data
+  },
+}
diff --git a/frontend/src/apis/chat/chat.keys.ts b/frontend/src/apis/chat/chat.keys.ts
new file mode 100644
index 0000000..fda0a83
--- /dev/null
+++ b/frontend/src/apis/chat/chat.keys.ts
@@ -0,0 +1,6 @@
+// 채팅 도메인의 TanStack Query 키 팩토리.
+export const chatKeys = {
+  all: ['chat'] as const,
+  init: (sessionId: string) => [...chatKeys.all, 'init', sessionId] as const,
+  messages: (sessionId: string) => [...chatKeys.all, 'messages', sessionId] as const,
+}
diff --git a/frontend/src/apis/chat/chat.mutations.ts b/frontend/src/apis/chat/chat.mutations.ts
new file mode 100644
index 0000000..fc4f439
--- /dev/null
+++ b/frontend/src/apis/chat/chat.mutations.ts
@@ -0,0 +1,14 @@
+// 채팅 도메인의 변경(useMutation) 훅.
+import { useMutation } from '@tanstack/react-query'
+import { chatApi } from './chat.api'
+import type { ChatSendRequest } from './chat.type'
+
+/**
+ * 협상 한 턴 전송. append-only 라 캐시 무효화/refetch 를 하지 않는다.
+ * 응답의 새 봇 메시지는 호출부(컨트롤러)가 스토어에 직접 append 한다.
+ */
+export function useChatSendMutation(sessionId: string) {
+  return useMutation({
+    mutationFn: (body: ChatSendRequest) => chatApi.send(sessionId, body),
+  })
+}
diff --git a/frontend/src/apis/chat/chat.queries.ts b/frontend/src/apis/chat/chat.queries.ts
new file mode 100644
index 0000000..824dd9e
--- /dev/null
+++ b/frontend/src/apis/chat/chat.queries.ts
@@ -0,0 +1,29 @@
+// 채팅 도메인의 조회(useQuery) 훅.
+import { useQuery } from '@tanstack/react-query'
+import { chatApi } from './chat.api'
+import { chatKeys } from './chat.keys'
+import { mapInit, mapMessage } from './chat.type'
+
+/** 채팅 진입 메타(상품·견적). 마감 시각은 거의 불변이라 오래 캐싱한다. */
+export function useChatInitQuery(sessionId: string) {
+  return useQuery({
+    queryKey: chatKeys.init(sessionId),
+    queryFn: () => chatApi.getInit(sessionId).then(mapInit),
+    enabled: !!sessionId,
+    staleTime: 5 * 60 * 1000,
+  })
+}
+
+/**
+ * 대화 히스토리. 진입 시 1회만 받고 이후엔 send 응답을 로컬에 append 한다(append-only).
+ * 따라서 백그라운드 refetch 가 로컬 상태를 덮지 않도록 staleTime 을 무한대로 둔다.
+ */
+export function useChatMessagesQuery(sessionId: string) {
+  return useQuery({
+    queryKey: chatKeys.messages(sessionId),
+    queryFn: () => chatApi.getMessages(sessionId).then((r) => r.items.map(mapMessage)),
+    enabled: !!sessionId,
+    staleTime: Infinity,
+    refetchOnWindowFocus: false,
+  })
+}
diff --git a/frontend/src/apis/chat/chat.type.ts b/frontend/src/apis/chat/chat.type.ts
new file mode 100644
index 0000000..dc6227b
--- /dev/null
+++ b/frontend/src/apis/chat/chat.type.ts
@@ -0,0 +1,103 @@
+// 채팅 API 의 와이어 타입(백엔드 snake_case 미러) + feature 타입 매퍼.
+// sender 는 정수 코드(1=BOT, 2=USER)로 내려오고 프론트에서 'bot'|'user' 로 매핑한다.
+import type { ApiResult } from '@/apis/types'
+import type {
+  ChatInitData,
+  ChatMessage,
+  NextInputMode,
+  UserInputType,
+} from '@/features/chat/types'
+
+// RemoveNoneResponse 로 null 필드는 생략될 수 있어 대부분 optional.
+export interface ChatMessageWire {
+  chat_id: string
+  session_id: string
+  seq: number
+  sender: number
+  script?: string
+  user_input_type?: string | null
+  step?: string
+  display_step?: string
+  next_input_mode?: string | null
+  next_input_type?: string[] | null
+  chat_end?: boolean
+  indicator_value?: number | null
+  bot_chat_type?: string | null
+}
+
+export interface ChatInitResponse {
+  result: ApiResult
+  session_id: string
+  session_status: number
+  quotation_id: string
+  quotation_end_time: string
+  quotation_memo?: string
+  item_id: string
+  item_name: string
+  item_code?: string
+  item_image?: string
+  item_price: number
+  item_model_name?: string
+  item_maker_name?: string
+  item_spec?: string
+  item_lead_time?: string
+  item_min_order_quantity?: string
+  item_vat_yn?: boolean
+  item_delivery_fee_yn?: boolean
+}
+
+export interface ChatMessagesResponse {
+  result: ApiResult
+  items: ChatMessageWire[]
+}
+
+export interface ChatSendRequest {
+  user_input: string
+  user_input_type?: string | null
+}
+
+export interface ChatSendResponse {
+  result: ApiResult
+  message?: ChatMessageWire
+  session_status: number
+}
+
+// --- 매퍼: 와이어 → feature 타입 --------------------------------------------
+export function mapMessage(w: ChatMessageWire): ChatMessage {
+  return {
+    chat_id: w.chat_id,
+    sender: w.sender === 1 ? 'bot' : 'user',
+    bot_chat_type: (w.bot_chat_type ?? null) as ChatMessage['bot_chat_type'],
+    user_input_type: (w.user_input_type ?? null) as UserInputType | null,
+    script: w.script ?? null,
+    chat_end: w.chat_end ?? false,
+    next_input_mode: (w.next_input_mode ?? null) as NextInputMode | null,
+    next_input_type: w.next_input_type ?? null,
+    step: w.step ?? '',
+    display_step: w.display_step ?? '',
+    summary: null, // (범위 외) 최종 요약 카드는 추후
+    indicator_value: w.indicator_value ?? null,
+  }
+}
+
+export function mapInit(r: ChatInitResponse): ChatInitData {
+  return {
+    session_id: r.session_id,
+    item_id: r.item_id,
+    quotation_id: r.quotation_id,
+    item_name: r.item_name,
+    item_code: r.item_code ?? '',
+    item_image: r.item_image ?? '',
+    item_price: r.item_price ?? 0,
+    item_model_name: r.item_model_name ?? '',
+    item_maker_name: r.item_maker_name ?? '',
+    item_vat_yn: r.item_vat_yn == null ? '' : r.item_vat_yn ? 'VAT포함' : 'VAT별도',
+    item_delivery_fee_yn:
+      r.item_delivery_fee_yn == null ? '' : r.item_delivery_fee_yn ? '배송비포함' : '배송비별도',
+    item_min_order_quantity: r.item_min_order_quantity ?? '',
+    item_lead_time: r.item_lead_time ?? '',
+    item_spec: r.item_spec ?? '',
+    quotation_memo: r.quotation_memo ?? '',
+    quotation_end_time: r.quotation_end_time ?? '',
+  }
+}
diff --git a/frontend/src/apis/chat/index.ts b/frontend/src/apis/chat/index.ts
new file mode 100644
index 0000000..2544c3a
--- /dev/null
+++ b/frontend/src/apis/chat/index.ts
@@ -0,0 +1,13 @@
+// 채팅 도메인 API 공개 표면.
+export { chatApi } from './chat.api'
+export { chatKeys } from './chat.keys'
+export { useChatInitQuery, useChatMessagesQuery } from './chat.queries'
+export { useChatSendMutation } from './chat.mutations'
+export { mapInit, mapMessage } from './chat.type'
+export type {
+  ChatInitResponse,
+  ChatMessagesResponse,
+  ChatMessageWire,
+  ChatSendRequest,
+  ChatSendResponse,
+} from './chat.type'
diff --git a/frontend/src/apis/index.ts b/frontend/src/apis/index.ts
index e707984..3985e59 100644
--- a/frontend/src/apis/index.ts
+++ b/frontend/src/apis/index.ts
@@ -6,3 +6,4 @@ export type { ApiResult, ApiEnvelope } from './types'
 
 export * from './auth'
 export * from './negotiation'
+export * from './chat'
diff --git a/frontend/src/apis/types.ts b/frontend/src/apis/types.ts
index 0115bf8..86d18ed 100644
--- a/frontend/src/apis/types.ts
+++ b/frontend/src/apis/types.ts
@@ -37,6 +37,10 @@ export const ErrorCode = {
   NEGO_QUOTATION_CLOSED: 1302,
   NEGO_DEADLINE_PASSED: 1303,
   NEGO_NOT_FOUND: 1304,
+  CHAT_NOT_IN_PROGRESS: 1400,
+  CHAT_PRICE_OUT_OF_RANGE: 1401,
+  CHAT_AGENT_UNAVAILABLE: 1402,
+  CHAT_IN_PROGRESS: 1403,
 } as const
 
 export type ErrorCode = (typeof ErrorCode)[keyof typeof ErrorCode]
@@ -54,6 +58,10 @@ const API_ERROR_MESSAGES: Record<number, string> = {
   [ErrorCode.NEGO_QUOTATION_CLOSED]: '마감된 견적입니다.',
   [ErrorCode.NEGO_DEADLINE_PASSED]: '협상 마감 시간이 지났습니다.',
   [ErrorCode.NEGO_NOT_FOUND]: '협상을 찾을 수 없습니다.',
+  [ErrorCode.CHAT_NOT_IN_PROGRESS]: '진행 중인 협상이 아닙니다. 목록으로 돌아갑니다.',
+  [ErrorCode.CHAT_PRICE_OUT_OF_RANGE]: '제시 가격이 허용 범위를 벗어났습니다.',
+  [ErrorCode.CHAT_AGENT_UNAVAILABLE]: '협상 처리 중 오류가 발생했습니다. 잠시 후 다시 시도해주세요.',
+  [ErrorCode.CHAT_IN_PROGRESS]: '이전 메시지를 처리 중입니다. 잠시만 기다려주세요.',
 }
 
 /** API 에러: result.code(비즈니스) 또는 HTTP status 를 code 로 담는다 */
diff --git a/frontend/src/features/chat/containers/ChatContainer.tsx b/frontend/src/features/chat/containers/ChatContainer.tsx
index adeb3b6..1159b38 100644
--- a/frontend/src/features/chat/containers/ChatContainer.tsx
+++ b/frontend/src/features/chat/containers/ChatContainer.tsx
@@ -1,10 +1,10 @@
-import { useChatInit } from '@/features/chat/hooks/useChatInit'
+import { useChatController } from '@/features/chat/hooks/useChatController'
 import { ChatSection } from '@/features/chat/components/ChatSection'
 import { MenuSection } from '@/features/chat/components/menu/MenuSection'
 
-// 콘텐츠 영역: 채팅 + 우측 메뉴. mock 데이터를 스토어에 적재한다.
-export function ChatContainer() {
-  useChatInit()
+// 콘텐츠 영역: 채팅 + 우측 메뉴. session_id 로 init/messages 를 적재하고 전송을 주입한다.
+export function ChatContainer({ sessionId }: { sessionId: string }) {
+  useChatController(sessionId)
   return (
     <div className="flex flex-1 min-h-0 w-full">
       <ChatSection />
diff --git a/frontend/src/features/chat/hooks/useChatController.ts b/frontend/src/features/chat/hooks/useChatController.ts
new file mode 100644
index 0000000..ae9f320
--- /dev/null
+++ b/frontend/src/features/chat/hooks/useChatController.ts
@@ -0,0 +1,113 @@
+import { useEffect } from 'react'
+import { useNavigate } from 'react-router'
+import { useChatInitQuery, useChatMessagesQuery, useChatSendMutation, mapMessage } from '@/apis/chat'
+import { ErrorCode, getApiErrorMessage, isApiError } from '@/apis/types'
+import { toast } from '@/lib'
+import { useChatStore } from '@/features/chat/stores/useChatStore'
+import { useChatInitStore } from '@/features/chat/stores/useChatInitStore'
+import type { ChatMessage, UserInputType } from '@/features/chat/types'
+
+// 더 이상 대화를 이어갈 수 없는(세션 종료/마감/권한) 코드 → 입력 잠금 후 목록으로 복귀.
+const TERMINAL_CODES = new Set<number>([
+  ErrorCode.CHAT_NOT_IN_PROGRESS,
+  ErrorCode.NEGO_QUOTATION_CLOSED,
+  ErrorCode.NEGO_DEADLINE_PASSED,
+  ErrorCode.NEGO_FORBIDDEN,
+  ErrorCode.NEGO_NOT_FOUND,
+])
+
+let tempSeq = 0
+
+// 낙관적 유저 말풍선 생성 (전송 즉시 표시). 서버 확정 메시지는 send 응답으로 append 한다.
+function makeUserMessage(text: string, inputType: UserInputType): ChatMessage {
+  return {
+    chat_id: `temp-user-${tempSeq++}`,
+    sender: 'user',
+    bot_chat_type: null,
+    user_input_type: inputType,
+    script: text,
+    chat_end: false,
+    next_input_mode: null,
+    next_input_type: null,
+    step: '',
+    display_step: '',
+    summary: null,
+    indicator_value: null,
+  }
+}
+
+/**
+ * 채팅 페이지 컨트롤러: init/messages 조회를 스토어에 적재하고,
+ * append-only 전송 구현을 스토어에 주입한다. (mock 을 대체)
+ */
+export function useChatController(sessionId: string) {
+  const navigate = useNavigate()
+  const setInitData = useChatInitStore((s) => s.setInitData)
+  const initQuery = useChatInitQuery(sessionId)
+  const messagesQuery = useChatMessagesQuery(sessionId)
+  const sendMutation = useChatSendMutation(sessionId)
+
+  // init 메타 → 스토어
+  useEffect(() => {
+    if (initQuery.data) setInitData(initQuery.data)
+  }, [initQuery.data, setInitData])
+
+  // 대화 히스토리 → 스토어 (진입 1회)
+  useEffect(() => {
+    if (messagesQuery.data) useChatStore.getState().setMessages(messagesQuery.data)
+  }, [messagesQuery.data])
+
+  // sessionId + 전송 구현 주입
+  useEffect(() => {
+    const store = useChatStore.getState()
+    store.setSessionId(sessionId)
+
+    store.bindSend((text, inputType = 'text') => {
+      const optimistic = makeUserMessage(text, inputType)
+      store.appendMessage(optimistic)
+      store.setIsLoading(true)
+      store.setPriceErrorMessage('')
+
+      sendMutation.mutate(
+        { user_input: text, user_input_type: inputType === 'text' ? null : inputType },
+        {
+          onSuccess: (data) => {
+            const s = useChatStore.getState()
+            if (data.message) s.appendMessage(mapMessage(data.message))
+            s.setIsLoading(false)
+          },
+          onError: (error) => {
+            const s = useChatStore.getState()
+            // 낙관적 메시지 롤백 (서버에 저장되지 않음)
+            s.setMessages(s.messages.filter((m) => m.chat_id !== optimistic.chat_id))
+            s.setIsLoading(false)
+            const code = isApiError(error) ? error.code : 0
+
+            // 가격 범위 초과: 입력창 인라인 에러로 표시(페이지 유지)
+            if (code === ErrorCode.CHAT_PRICE_OUT_OF_RANGE) {
+              s.setPriceErrorMessage(getApiErrorMessage(error))
+              return
+            }
+
+            toast.error(getApiErrorMessage(error, '협상 처리 중 오류가 발생했습니다.'))
+
+            // 마감/종료/권한 등 더 진행 불가한 상태면 잠시 후 목록으로 복귀
+            if (TERMINAL_CODES.has(code)) {
+              s.bindSend(null) // 입력 잠금(추가 전송 차단)
+              setTimeout(() => navigate('/list'), 1500)
+            }
+          },
+        },
+      )
+    })
+
+    return () => {
+      useChatStore.getState().reset()
+    }
+  }, [sessionId, sendMutation, navigate])
+
+  return {
+    isInitLoading: initQuery.isLoading || messagesQuery.isLoading,
+    initError: initQuery.error ?? messagesQuery.error,
+  }
+}
diff --git a/frontend/src/features/chat/hooks/useChatInit.ts b/frontend/src/features/chat/hooks/useChatInit.ts
deleted file mode 100644
index c87a008..0000000
--- a/frontend/src/features/chat/hooks/useChatInit.ts
+++ /dev/null
@@ -1,16 +0,0 @@
-import { useEffect } from 'react'
-import { useChatStore } from '@/features/chat/stores/useChatStore'
-import { useChatInitStore } from '@/features/chat/stores/useChatInitStore'
-import { MOCK_CHAT_INIT } from '@/features/chat/mocks/mockChatInit'
-import { MOCK_MESSAGES } from '@/features/chat/mocks/mockMessages'
-
-// mock 세션/대화 데이터를 스토어에 적재 (추후 API 조회로 교체)
-export function useChatInit() {
-  const setInitData = useChatInitStore((s) => s.setInitData)
-  const setMessages = useChatStore((s) => s.setMessages)
-
-  useEffect(() => {
-    setInitData(MOCK_CHAT_INIT)
-    setMessages(MOCK_MESSAGES)
-  }, [setInitData, setMessages])
-}
diff --git a/frontend/src/features/chat/lib/remainingTime.ts b/frontend/src/features/chat/lib/remainingTime.ts
index f483a78..ad383c8 100644
--- a/frontend/src/features/chat/lib/remainingTime.ts
+++ b/frontend/src/features/chat/lib/remainingTime.ts
@@ -1,4 +1,6 @@
 // 마감까지 남은 시간 'HH시간 MM분 SS초'. 지났으면 종료 문구, 잘못된 값은 '-'.
+// 남은 시간은 "절대 시각 간 차이(duration)"라 타임존과 무관하다. 백엔드가 UTC(+00:00 오프셋 포함)로
+// 내려주므로 new Date 파싱이 정확하면 KST 변환이 따로 필요 없다(날짜로 "표시"할 때만 KST 고정 필요 → lib/datetime).
 export function getTimeRemaining(targetDateTime: string | Date): string {
   const now = Date.now()
   const target = new Date(targetDateTime).getTime()
diff --git a/frontend/src/features/chat/mocks/mockChatInit.ts b/frontend/src/features/chat/mocks/mockChatInit.ts
deleted file mode 100644
index a9840fb..0000000
--- a/frontend/src/features/chat/mocks/mockChatInit.ts
+++ /dev/null
@@ -1,25 +0,0 @@
-import type { ChatInitData } from '@/features/chat/types'
-
-// 마감까지 카운트다운이 보이도록 현재 시각 기준 미래로 설정
-const END_TIME = new Date(Date.now() + 95 * 60 * 1000).toISOString()
-
-// 임시 세션/상품 데이터 (API 연동 전)
-export const MOCK_CHAT_INIT: ChatInitData = {
-  session_id: 's-001',
-  item_id: 'item-001',
-  quotation_id: 'qt-001',
-  item_name: '사무용 노트북 14인치',
-  item_code: 'IMK-10231',
-  item_image: '',
-  item_price: 1350000,
-  item_model_name: 'NB-1400-PRO',
-  item_maker_name: '삼성전자',
-  item_vat_yn: 'VAT별도',
-  item_delivery_fee_yn: 'N',
-  item_min_order_quantity: '10 EA',
-  item_lead_time: '7일',
-  item_spec: 'Intel Core i7 / 16GB RAM / 512GB SSD / 14인치 FHD',
-  quotation_memo:
-    '납기 엄수 부탁드립니다.\n세금계산서는 월말 일괄 발행합니다.\n상세 사양은 첨부 문서를 확인해주세요.',
-  quotation_end_time: END_TIME,
-}
diff --git a/frontend/src/features/chat/mocks/mockMessages.ts b/frontend/src/features/chat/mocks/mockMessages.ts
deleted file mode 100644
index 34a299b..0000000
--- a/frontend/src/features/chat/mocks/mockMessages.ts
+++ /dev/null
@@ -1,106 +0,0 @@
-import type { ChatMessage, ChatSummary } from '@/features/chat/types'
-
-// 전 메시지 템플릿을 한눈에 보기 위한 쇼케이스 목 대화 (실제 협상 흐름 아님)
-
-const SUMMARY: ChatSummary = {
-  md_name: '김엠디',
-  item_moq: '10 EA',
-  md_email: 'md@example.com',
-  item_code: 'IMK-10231',
-  item_name: '사무용 노트북 14인치',
-  item_spec: 'Intel Core i7 / 16GB / 512GB SSD',
-  item_isVAT: false,
-  item_maker: '삼성전자',
-  item_model: 'NB-1400-PRO',
-  final_price: 1200000,
-  nego_end_date: '2026년 06월 17일 14시 30분',
-  supplier_name: '대한상사',
-  item_lead_time: '7일',
-  md_phone_number: '02-1234-5678',
-  nego_start_date: '2026년 06월 17일 14시 00분',
-  item_display_date: '2026년 06월 10일',
-  item_delivery_type: '협력사배송',
-  supplier_manager_name: '이담당',
-  supplier_manager_email: 'sales@example.com',
-  delivery_type: '협력사배송',
-}
-
-const base = {
-  bot_chat_type: null,
-  user_input_type: null,
-  script: null,
-  chat_end: false,
-  next_input_mode: null,
-  next_input_type: null,
-  summary: null,
-  indicator_value: null,
-} as const
-
-export const MOCK_MESSAGES: ChatMessage[] = [
-  {
-    ...base,
-    chat_id: 'm1',
-    sender: 'bot',
-    script:
-      '안녕하세요, 협상을 시작하겠습니다. 본 협상은 자동으로 진행되며, 안내에 따라 응답해주시면 됩니다.',
-    step: '서비스안내',
-    display_step: '서비스안내',
-  },
-  {
-    ...base,
-    chat_id: 'm2',
-    sender: 'bot',
-    bot_chat_type: 'indicator',
-    indicator_value: 62,
-    script: '현재까지의 협상 성공률은 아래와 같습니다.',
-    step: '가격협상',
-    display_step: '가격협상',
-  },
-  {
-    ...base,
-    chat_id: 'm3',
-    sender: 'user',
-    user_input_type: 'price',
-    script: '1,200,000원',
-    step: '가격협상',
-    display_step: '가격협상',
-  },
-  {
-    ...base,
-    chat_id: 'm4',
-    sender: 'bot',
-    bot_chat_type: 'summaryCM',
-    summary: SUMMARY,
-    script: '제시해주신 금액으로 투찰 결과를 요약해드립니다.',
-    step: '가격협상',
-    display_step: '가격협상',
-  },
-  {
-    ...base,
-    chat_id: 'm5',
-    sender: 'bot',
-    bot_chat_type: 'summaryRSP',
-    summary: SUMMARY,
-    script: '협상이 완료되었습니다. 최종 결과를 요약해드립니다.',
-    step: '협상종료',
-    display_step: '협상종료',
-  },
-  {
-    ...base,
-    chat_id: 'm6',
-    sender: 'bot',
-    bot_chat_type: 'rejectCM',
-    script: '제시 금액이 수용되지 않았습니다. 최종 공급 희망 가격과 배송 형태를 입력해주세요.',
-    step: '가격협상',
-    display_step: '가격협상',
-  },
-  {
-    ...base,
-    chat_id: 'm7',
-    sender: 'bot',
-    script: '추가로 제시할 가격이 있다면 입력해주세요.',
-    next_input_mode: 'price',
-    step: '가격협상',
-    display_step: '가격협상',
-  },
-]
diff --git a/frontend/src/features/chat/stores/useChatStore.ts b/frontend/src/features/chat/stores/useChatStore.ts
index 18ec603..c4b8b18 100644
--- a/frontend/src/features/chat/stores/useChatStore.ts
+++ b/frontend/src/features/chat/stores/useChatStore.ts
@@ -2,24 +2,39 @@ import { create } from 'zustand'
 import type { ChatMessage, UserButtonConfig, UserInputType } from '@/features/chat/types'
 import { deriveUserButtonConfig } from '@/features/chat/lib/userButtonConfig'
 
+type SendFn = (text: string, inputType?: UserInputType) => void
+
 type ChatStore = {
+  sessionId: string
   messages: ChatMessage[]
   userButtonConfig: UserButtonConfig
   isLoading: boolean
   priceErrorMessage: string
+  setSessionId: (sessionId: string) => void
   setMessages: (messages: ChatMessage[]) => void
+  appendMessage: (message: ChatMessage) => void
   setIsLoading: (isLoading: boolean) => void
   setPriceErrorMessage: (message: string) => void
-  sendMessage: (text: string, inputType?: UserInputType) => void
+  // 실제 전송 구현은 컨트롤러(useChatController)가 React Query 와 함께 주입한다.
+  bindSend: (fn: SendFn | null) => void
+  sendMessage: SendFn
+  reset: () => void
 }
 
-let mockSeq = 0
-
-export const useChatStore = create<ChatStore>((set, get) => ({
-  messages: [],
-  userButtonConfig: { type: '', text: '' },
+const initial = {
+  sessionId: '',
+  messages: [] as ChatMessage[],
+  userButtonConfig: { type: '' } as UserButtonConfig,
   isLoading: false,
   priceErrorMessage: '',
+}
+
+let sendImpl: SendFn | null = null
+
+export const useChatStore = create<ChatStore>((set, get) => ({
+  ...initial,
+
+  setSessionId: (sessionId) => set({ sessionId }),
 
   setMessages: (messages) =>
     set((s) => ({
@@ -27,6 +42,12 @@ export const useChatStore = create<ChatStore>((set, get) => ({
       userButtonConfig: deriveUserButtonConfig(messages, s.isLoading, s.priceErrorMessage),
     })),
 
+  appendMessage: (message) =>
+    set((s) => {
+      const messages = [...s.messages, message]
+      return { messages, userButtonConfig: deriveUserButtonConfig(messages, s.isLoading, s.priceErrorMessage) }
+    }),
+
   setIsLoading: (isLoading) =>
     set((s) => ({
       isLoading,
@@ -39,25 +60,17 @@ export const useChatStore = create<ChatStore>((set, get) => ({
       userButtonConfig: deriveUserButtonConfig(s.messages, s.isLoading, priceErrorMessage),
     })),
 
-  // mock: API 미연동이라 사용자 메시지를 로컬에 추가만 한다 (실제 협상 진행 로직 없음)
+  bindSend: (fn) => {
+    sendImpl = fn
+  },
+
   sendMessage: (text, inputType = 'text') => {
-    const { messages } = get()
-    const last = messages[messages.length - 1]
-    const userMsg: ChatMessage = {
-      chat_id: `mock-user-${mockSeq++}`,
-      sender: 'user',
-      bot_chat_type: null,
-      user_input_type: inputType,
-      script: text,
-      chat_end: false,
-      next_input_mode: null,
-      next_input_type: null,
-      step: last?.step ?? '',
-      display_step: last?.display_step ?? '',
-      summary: null,
-      indicator_value: null,
-    }
-    const next = [...messages, userMsg]
-    set({ messages: next, priceErrorMessage: '', userButtonConfig: deriveUserButtonConfig(next, false, '') })
+    if (get().isLoading) return
+    sendImpl?.(text, inputType)
+  },
+
+  reset: () => {
+    sendImpl = null
+    set({ ...initial })
   },
 }))
diff --git a/frontend/src/features/list/lib/datetime.ts b/frontend/src/features/list/lib/datetime.ts
index 80da812..9e821f9 100644
--- a/frontend/src/features/list/lib/datetime.ts
+++ b/frontend/src/features/list/lib/datetime.ts
@@ -1,8 +1,6 @@
-// 'YYYY-MM-DD HH:mm'. 빈 값 '-', 파싱 실패 시 원본.
+import { formatKstDateTime } from '@/lib'
+
+// 'YYYY-MM-DD HH:mm' (KST 고정). 백엔드 UTC 직렬화를 한국 시간으로 표시한다.
 export function formatDateTime(value: string): string {
-  if (!value) return '-'
-  const d = new Date(value)
-  if (Number.isNaN(d.getTime())) return value
-  const pad = (n: number) => String(n).padStart(2, '0')
-  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())} ${pad(d.getHours())}:${pad(d.getMinutes())}`
+  return formatKstDateTime(value)
 }
diff --git a/frontend/src/lib/datetime.ts b/frontend/src/lib/datetime.ts
new file mode 100644
index 0000000..2f5701e
--- /dev/null
+++ b/frontend/src/lib/datetime.ts
@@ -0,0 +1,29 @@
+// 시각 표시 유틸. 백엔드는 모든 시각을 UTC(+00:00 오프셋 포함 ISO)로 직렬화하므로,
+// 절대 시각 파싱은 브라우저 타임존과 무관하게 정확하다. 다만 "표시"는 항상 KST(Asia/Seoul)로
+// 고정해야 한국 외 타임존 브라우저에서도 동일한 마감 시각을 보여줄 수 있다.
+export const KST_TIME_ZONE = 'Asia/Seoul'
+
+// hourCycle:'h23' → 자정을 24 가 아닌 00 으로(엔진별 '24:00' 방지). locale 무관 고정 포맷.
+const kstFormat = new Intl.DateTimeFormat('en-CA', {
+  timeZone: KST_TIME_ZONE,
+  year: 'numeric',
+  month: '2-digit',
+  day: '2-digit',
+  hour: '2-digit',
+  minute: '2-digit',
+  hourCycle: 'h23',
+})
+
+function toKstParts(value: string | Date): Record<string, string> | null {
+  const d = value instanceof Date ? value : new Date(value)
+  if (Number.isNaN(d.getTime())) return null
+  return Object.fromEntries(kstFormat.formatToParts(d).map((p) => [p.type, p.value]))
+}
+
+/** 'YYYY-MM-DD HH:mm' (KST). 빈 값 '-', 파싱 실패 시 원본 문자열. */
+export function formatKstDateTime(value: string | Date): string {
+  if (!value) return '-'
+  const p = toKstParts(value)
+  if (!p) return typeof value === 'string' ? value : '-'
+  return `${p.year}-${p.month}-${p.day} ${p.hour}:${p.minute}`
+}
diff --git a/frontend/src/lib/index.ts b/frontend/src/lib/index.ts
index b8bb278..f3d7612 100644
--- a/frontend/src/lib/index.ts
+++ b/frontend/src/lib/index.ts
@@ -3,3 +3,4 @@ export { cn } from '@/lib/cn'
 export type { ClassValue } from '@/lib/cn'
 export { interactive } from '@/lib/interactive'
 export { toast } from '@/lib/toast'
+export { formatKstDateTime, KST_TIME_ZONE } from '@/lib/datetime'
diff --git a/frontend/src/pages/ChatPage.tsx b/frontend/src/pages/ChatPage.tsx
index ace7989..3a690ca 100644
--- a/frontend/src/pages/ChatPage.tsx
+++ b/frontend/src/pages/ChatPage.tsx
@@ -1,4 +1,4 @@
-import { useNavigate } from 'react-router'
+import { useNavigate, useSearchParams, Navigate } from 'react-router'
 import { List } from 'lucide-react'
 import { cn, interactive } from '@/lib'
 import { MainLayout, MainHeaderBar } from '@/layouts'
@@ -6,6 +6,12 @@ import { ChatContainer, ItemSection, RemainingTime } from '@/features/chat'
 import { SidebarFooter } from '@/features/auth'
 
 export function ChatPage() {
+  const [searchParams] = useSearchParams()
+  const sessionId = searchParams.get('session_id') ?? ''
+
+  // session_id 없이 진입하면 목록으로 되돌린다.
+  if (!sessionId) return <Navigate to="/list" replace />
+
   return (
     <MainLayout
       sidebarWidth="chat"
@@ -18,7 +24,7 @@ export function ChatPage() {
         </MainHeaderBar>
       }
     >
-      <ChatContainer />
+      <ChatContainer sessionId={sessionId} />
     </MainLayout>
   )
 }