feat(ios): IOS-M0-01 RAG Chat 接入真实 API

- 新增 RagChatService: createSession/listSessions/getMessages/sendMessage/deleteSession
- 新增 ChatSession/ChatMessage/SendMessageResponse 等数据模型
- AIChatViewModel 重写：移除 mock，调用真实 /rag-chat API
- 自动选择知识库创建对话 session
- AIChatPage 增加加载态（创建 session 中）和错误态（无知识库）
- send() → POST /rag-chat/sessions/:id/messages 返回真实 AI 回复

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AIStudyApp/AIStudyApp/Core/Models/APIModels.swift

@@ -392,6 +392,52 @@ struct BatchDeleteResponse: Codable {
     let count: Int?
 }
 
+// MARK: - RAG Chat
+
+struct ChatSession: Codable, Identifiable {
+    let id: String
+    let userId: String?
+    let knowledgeBaseId: String?
+    let title: String?
+    let createdAt: String?
+    let updatedAt: String?
+}
+
+struct ChatMessage: Codable, Identifiable {
+    let id: String
+    let sessionId: String?
+    let role: String
+    let content: String
+    let tokens: Int?
+    let createdAt: String?
+    let citations: [ChatCitation]?
+}
+
+struct ChatCitation: Codable, Identifiable {
+    let id: String
+    let chunkId: String?
+    let content: String?
+    let score: Double?
+}
+
+struct CreateSessionRequest: Codable {
+    let knowledgeBaseId: String
+    let title: String?
+}
+
+struct SendMessageRequest: Codable {
+    let content: String
+}
+
+struct SendMessageResponse: Codable {
+    let id: String?
+    let role: String?
+    let content: String?
+    let tokens: Int?
+    let blocked: Bool?
+    let message: String?
+}
+
 // MARK: - File Upload (COS presigned URL flow)
 
 struct FileUploadUrlRequest: Codable {

AIStudyApp/AIStudyApp/Core/Services/APIService.swift

@@ -273,6 +273,36 @@ class FeedbackService {
     }
 }
 
+// MARK: - RAG Chat
+
+@MainActor
+class RagChatService {
+    static let shared = RagChatService()
+    private let client = APIClient.shared
+
+    func createSession(knowledgeBaseId: String, title: String? = nil) async throws -> ChatSession {
+        let body = CreateSessionRequest(knowledgeBaseId: knowledgeBaseId, title: title)
+        return try await client.request("/rag-chat/sessions", method: "POST", body: body)
+    }
+
+    func listSessions() async throws -> [ChatSession] {
+        return try await client.request("/rag-chat/sessions")
+    }
+
+    func getMessages(sessionId: String) async throws -> [ChatMessage] {
+        return try await client.request("/rag-chat/sessions/\(sessionId)/messages")
+    }
+
+    func sendMessage(sessionId: String, content: String) async throws -> SendMessageResponse {
+        let body = SendMessageRequest(content: content)
+        return try await client.request("/rag-chat/sessions/\(sessionId)/messages", method: "POST", body: body)
+    }
+
+    func deleteSession(id: String) async throws {
+        let _: GenericSuccessResponse = try await client.request("/rag-chat/sessions/\(id)", method: "DELETE")
+    }
+}
+
 // MARK: - Notifications
 
 @MainActor

AIStudyApp/AIStudyApp/Features/AI/AIChatPage.swift

@@ -7,12 +7,22 @@ struct AIChatPage: View {
         ZStack {
             Color.zxBg0.ignoresSafeArea()
             VStack(spacing: 0) {
+                if vm.isCreatingSession {
+                    VStack(spacing: 12) {
+                        ProgressView().tint(Color.zxPurple)
+                        Text("正在准备 AI 助手...").font(.system(size: 13)).foregroundColor(Color.zxF04)
+                    }.frame(maxWidth: .infinity, maxHeight: .infinity)
+                } else if let error = vm.sessionError {
+                    VStack(spacing: 16) {
+                        Image(systemName: "exclamationmark.triangle").font(.system(size: 36)).foregroundColor(Color.zxF04)
+                        Text(error).font(.system(size: 14)).foregroundColor(Color.zxF04)
+                    }.frame(maxWidth: .infinity, maxHeight: .infinity)
+                } else {
                     ScrollViewReader { proxy in
                         ScrollView {
                             VStack(spacing: 16) {
                                 ForEach(vm.messages) { m in
-                                chatBubble(m)
-                                    .id(m.id)
+                                    chatBubble(m).id(m.id)
                                 }
                                 if vm.isSending {
                                     HStack(spacing: 8) {
@@ -20,11 +30,9 @@ struct AIChatPage: View {
                                             .frame(width: 28, height: 28)
                                             .background(Color(hex: "#7C6EFA", opacity: 0.15))
                                             .clipShape(Circle())
-                                    ZXDotLoader(color: Color.zxPurple)
-                                        .padding(.leading, 4)
+                                        ZXDotLoader(color: Color.zxPurple).padding(.leading, 4)
                                         Spacer()
-                                }
-                                .padding(.horizontal, 20)
+                                    }.padding(.horizontal, 20)
                                 }
                             }
                             .padding(.horizontal, 20).padding(.top, 8).padding(.bottom, 100)
@@ -38,8 +46,10 @@ struct AIChatPage: View {
                         .padding(.horizontal, 20).padding(.bottom, 34)
                 }
             }
+        }
         .navigationBarTitleDisplayMode(.inline).animatedTabBarHide()
         .toolbarBackground(.hidden, for: .navigationBar)
+        .task { await vm.load() }
     }
 
     private func chatBubble(_ m: AIMessage) -> some View {

AIStudyApp/AIStudyApp/Features/AI/AIChatViewModel.swift

@@ -13,30 +13,72 @@ enum AIMessageRole {
 
 @MainActor
 final class AIChatViewModel: ObservableObject {
-    @Published var messages: [AIMessage] = [
-        AIMessage(role: .ai, content: "你好！我是你的 AI 学习助手。")
-    ]
+    @Published var messages: [AIMessage] = []
     @Published var inputText = ""
     @Published var isSending = false
+    @Published var isCreatingSession = false
+    @Published var sessionError: String?
+
+    private var sessionId: String?
+    private var knowledgeBaseId: String?
 
     var canSend: Bool {
-        !inputText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty && !isSending
+        !inputText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty && !isSending && sessionId != nil
+    }
+
+    var isReady: Bool { sessionId != nil }
+
+    func load() async {
+        guard sessionId == nil else { return }
+
+        // 自动选一个知识库
+        if knowledgeBaseId == nil {
+            do {
+                let kbs = try await KnowledgeBaseService.shared.list(page: 1, limit: 1)
+                knowledgeBaseId = kbs.first?.id
+            } catch {}
+        }
+
+        guard let kbId = knowledgeBaseId else {
+            sessionError = "请先创建一个知识库，才能使用 AI 对话"
+            return
+        }
+
+        isCreatingSession = true
+        do {
+            let session = try await RagChatService.shared.createSession(knowledgeBaseId: kbId, title: nil)
+            sessionId = session.id
+            messages = [AIMessage(role: .ai, content: "你好！我是你的 AI 学习助手，基于你的知识库回答问题。")]
+            isCreatingSession = false
+        } catch {
+            sessionError = "创建对话失败"
+            isCreatingSession = false
+        }
     }
 
     func send() {
-        guard canSend else { return }
+        guard canSend, let sid = sessionId else { return }
         let text = inputText.trimmingCharacters(in: .whitespacesAndNewlines)
         messages.append(AIMessage(role: .user, content: text))
         inputText = ""
         isSending = true
 
         Task {
-            try? await Task.sleep(nanoseconds: 1_200_000_000)
-            messages.append(AIMessage(
-                role: .ai,
-                content: "好的，我理解你的问题。需要我帮你制定学习计划吗？"
-            ))
+            do {
+                let resp = try await RagChatService.shared.sendMessage(sessionId: sid, content: text)
+                if resp.blocked == true {
+                    messages.append(AIMessage(role: .ai, content: resp.message ?? "内容违规，请修改后重试"))
+                } else {
+                    messages.append(AIMessage(role: .ai, content: resp.content ?? "抱歉，AI 暂时无法回复"))
+                }
+            } catch {
+                messages.append(AIMessage(role: .ai, content: "发送失败: \(error.localizedDescription)"))
+            }
             isSending = false
         }
     }
+
+    func setKnowledgeBase(_ id: String) {
+        knowledgeBaseId = id
+    }
 }