diff --git a/src/app/api/chat/lib/chat-store.ts b/src/app/api/chat/lib/chat-store.ts
new file mode 100644
index 0000000..a4c6d9d
--- /dev/null
+++ b/src/app/api/chat/lib/chat-store.ts
@@ -0,0 +1,129 @@
+type ChatLocale = 'zh' | 'en'
+type ChatRole = 'USER' | 'ASSISTANT' | 'SYSTEM'
+type ChatStatus = 'ACTIVE'
+
+interface ChatMessage {
+  id: string
+  sessionId: string
+  role: ChatRole
+  contentText: string
+  mode: string | null
+  createdAt: string
+}
+
+interface ChatSession {
+  id: string
+  clientId: string
+  locale: ChatLocale
+  title: string
+  status: ChatStatus
+  createdAt: string
+  updatedAt: string
+  lastMessageAt: string
+}
+
+interface ChatStoreState {
+  sessions: Map<string, ChatSession>
+  messages: Map<string, ChatMessage[]>
+}
+
+declare global {
+  // eslint-disable-next-line no-var
+  var __agentParkChatStore: ChatStoreState | undefined
+}
+
+function getStore(): ChatStoreState {
+  if (!globalThis.__agentParkChatStore) {
+    globalThis.__agentParkChatStore = {
+      sessions: new Map<string, ChatSession>(),
+      messages: new Map<string, ChatMessage[]>(),
+    }
+  }
+
+  return globalThis.__agentParkChatStore
+}
+
+function nowIso(): string {
+  return new Date().toISOString()
+}
+
+export async function createChatSession(input: {
+  clientId: string
+  locale: ChatLocale
+  title?: string
+}): Promise<ChatSession> {
+  const store = getStore()
+  const now = nowIso()
+
+  const session: ChatSession = {
+    id: crypto.randomUUID(),
+    clientId: input.clientId,
+    locale: input.locale,
+    title: input.title?.trim() || 'New Chat',
+    status: 'ACTIVE',
+    createdAt: now,
+    updatedAt: now,
+    lastMessageAt: now,
+  }
+
+  store.sessions.set(session.id, session)
+  store.messages.set(session.id, [])
+
+  return session
+}
+
+export async function listChatSessions(input: {
+  clientId: string
+  locale?: ChatLocale
+  limit: number
+  cursor?: string
+}): Promise<Array<ChatSession & { messages: ChatMessage[] }>> {
+  const store = getStore()
+
+  const ordered = Array.from(store.sessions.values())
+    .filter((session) =>
+      input.locale
+        ? session.clientId === input.clientId && session.locale === input.locale
+        : session.clientId === input.clientId
+    )
+    .sort((a, b) => b.lastMessageAt.localeCompare(a.lastMessageAt))
+
+  const cursorIndex = input.cursor ? ordered.findIndex((session) => session.id === input.cursor) : -1
+  const page = cursorIndex >= 0 ? ordered.slice(cursorIndex + 1, cursorIndex + 1 + input.limit) : ordered.slice(0, input.limit)
+
+  return page.map((session) => {
+    const messageList = store.messages.get(session.id) || []
+    const latest = messageList.length > 0 ? [messageList[messageList.length - 1] as ChatMessage] : []
+    return {
+      ...session,
+      messages: latest,
+    }
+  })
+}
+
+export async function assertSessionOwnership(input: {
+  sessionId: string
+  clientId: string
+}): Promise<void> {
+  const store = getStore()
+  const session = store.sessions.get(input.sessionId)
+
+  if (!session) {
+    throw new Error('CHAT_SESSION_NOT_FOUND')
+  }
+
+  if (session.clientId !== input.clientId) {
+    throw new Error('CHAT_SESSION_FORBIDDEN')
+  }
+}
+
+export async function listChatMessages(input: {
+  sessionId: string
+  limit: number
+}): Promise<ChatMessage[]> {
+  const store = getStore()
+  const messages = store.messages.get(input.sessionId) || []
+  const normalizedLimit = Math.max(1, input.limit)
+
+  return messages.slice(-normalizedLimit)
+}
diff --git a/src/app/api/signals/route.ts b/src/app/api/signals/route.ts
index 418efaa..6eeaa76 100644
--- a/src/app/api/signals/route.ts
+++ b/src/app/api/signals/route.ts
@@ -232,13 +232,6 @@ export async function GET(request: NextRequest) {
         ? [{ isHot: 'desc' }, { hotScore: 'desc' }, { engagement: 'desc' }, { publishedAt: 'desc' }, { id: 'desc' }]
         : [{ publishedAt: 'desc' }, { id: 'desc' }]
 
-    const cursorArgs = parsed.cursor
-      ? {
-          cursor: { id: parsed.cursor },
-          skip: 1 as const,
-        }
-      : {}
-
     let rows: Array<{
       id: string
       source: string
@@ -262,7 +255,8 @@ export async function GET(request: NextRequest) {
         where,
         orderBy,
         take: parsed.limit + 1,
-        ...cursorArgs,
+        cursor: parsed.cursor ? { id: parsed.cursor } : undefined,
+        skip: parsed.cursor ? 1 : undefined,
         select: {
           id: true,
           source: true,
@@ -293,7 +287,8 @@ export async function GET(request: NextRequest) {
         where,
         orderBy: fallbackOrderBy,
         take: parsed.limit + 1,
-        ...cursorArgs,
+        cursor: parsed.cursor ? { id: parsed.cursor } : undefined,
+        skip: parsed.cursor ? 1 : undefined,
         select: {
           id: true,
           source: true,