fix(IOS-INFO-043): change source list nav to MaterialReaderView + add COS download

- LibraryDetailPage source list: Route.materialDetail → Route.materialReader
- KnowledgeSource: add fileId field for COS download
- MaterialReaderView: add COS download fallback in .task
- MaterialReaderView: add resolvedPath for downloaded file

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

AIStudyApp/AIStudyApp/Core/Models/APIModels.swift

@@ -630,6 +630,7 @@ struct CreateFolderRequest: Codable {
 struct KnowledgeSource: Codable, Identifiable {
     let id: String
     let knowledgeBaseId: String?
+    let fileId: String?
     let title: String?
     let originalFilename: String?
     let type: String?

AIStudyApp/AIStudyApp/Features/Library/LibrarySubpages.swift

@@ -262,13 +262,12 @@ struct LibraryDetailPage: View {
                                 Text("暂无资料来源").font(.system(size: 14)).foregroundColor(Color.zxF03).padding(.top, 40)
                             } else {
                                 ForEach(sources) { src in
-                                    NavigationLink(value: Route.materialDetail(
-                                        knowledgeBaseId: knowledgeBaseId,
-                                        fileName: src.originalFilename ?? src.title ?? "未命名",
-                                        fileType: materialTypeFromMime(src.mimeType),
-                                        fileSize: 0,
+                                    NavigationLink(value: Route.materialReader(
+                                        materialId: src.id,
                                         filePath: "",
-                                        uploadDate: src.createdAt
+                                        materialType: materialTypeFromMime(src.mimeType),
+                                        knowledgeBaseId: knowledgeBaseId,
+                                        title: src.originalFilename ?? src.title ?? "未命名"
                                     )) {
                                         HStack(spacing: 12) {
                                             Image(systemName: src.type == "file" ? "doc" : "link")

AIStudyApp/AIStudyApp/Features/MaterialReader/MaterialReaderView.swift

@@ -109,10 +109,19 @@ struct MaterialReaderView: View {
     @Environment(\.scenePhase) private var scenePhase
     @State private var isParsing = false
     @State private var parseMessage = ""
+    @State private var downloadedFilePath: String?
 
     private let title: String
     private let knowledgeBaseId: String?
 
+    /// Resolved file path: uses downloaded temp file if original is empty/missing
+    private var resolvedPath: String {
+        if !vm.filePath.isEmpty && FileManager.default.fileExists(atPath: vm.filePath) {
+            return vm.filePath
+        }
+        return downloadedFilePath ?? vm.filePath
+    }
+
     // V2 session manager (primary) + V1 collector (fallback)
     private let sessionManager = ReadingRuntimeSessionManager.shared
     private let collector = ReadingEventCollector.shared
@@ -239,7 +248,30 @@ struct MaterialReaderView: View {
                 .padding(.bottom, 100)
             }
         }
-        .task { await vm.load() }
+        .task {
+            if vm.filePath.isEmpty || !FileManager.default.fileExists(atPath: vm.filePath) {
+                if let kbId = knowledgeBaseId {
+                    print("[MaterialReader] No local file, downloading from COS: \(vm.materialId)")
+                    do {
+                        let source = try await KnowledgeSourceService.shared.detail(kbId: kbId, id: vm.materialId)
+                        if let fileId = source.fileId {
+                            let downloadUrl = try await FileUploadService.shared.getDownloadUrl(fileId: fileId)
+                            let url = URL(string: downloadUrl)!
+                            let (data, _) = try await URLSession.shared.data(from: url)
+                            let ext = source.originalFilename?.split(separator: ".").last.map(String.init) ?? "md"
+                            let localURL = FileManager.default.temporaryDirectory
+                                .appendingPathComponent("source_\(vm.materialId).\(ext)")
+                            try data.write(to: localURL)
+                            downloadedFilePath = localURL.path
+                            print("[MaterialReader] Downloaded to: \(localURL.path), size: \(data.count)")
+                        }
+                    } catch {
+                        print("[MaterialReader] COS download failed: \(error.localizedDescription)")
+                    }
+                }
+            }
+            await vm.load()
+        }
         .sheet(isPresented: $showQuickLook) {
             QuickLookPreview(url: URL(fileURLWithPath: vm.filePath))
         }