diff --git a/internal/app/cli.go b/internal/app/cli.go
new file mode 100644
index 0000000..973c1e3
--- /dev/null
+++ b/internal/app/cli.go
@@ -0,0 +1,296 @@
+package app
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const defaultUIListenAddress = "0.0.0.0:8999"
+
+type boolOverride struct {
+	set bool
+	val bool
+}
+
+func (b *boolOverride) String() string { return strconv.FormatBool(b.val) }
+
+func (b *boolOverride) Set(s string) error {
+	v, err := strconv.ParseBool(s)
+	if err != nil {
+		return err
+	}
+	b.set = true
+	b.val = v
+	return nil
+}
+
+func openBrowser(rawURL string) {
+	var cmd *exec.Cmd
+	switch runtime.GOOS {
+	case "darwin":
+		cmd = exec.Command("open", rawURL)
+	case "windows":
+		cmd = exec.Command("rundll32", "url.dll,FileProtocolHandler", rawURL)
+	default:
+		cmd = exec.Command("xdg-open", rawURL)
+	}
+	if err := cmd.Start(); err != nil {
+		fmt.Printf("  自动打开浏览器失败，请手动访问：%s (%v)\n", rawURL, err)
+	}
+}
+
+func normalizeListen(addr string) string {
+	addr = strings.TrimSpace(addr)
+	if addr == "" {
+		return defaultUIListenAddress
+	}
+	if strings.HasPrefix(addr, ":") {
+		return "0.0.0.0" + addr
+	}
+	return addr
+}
+
+func publicURL(addr string) string {
+	if strings.HasPrefix(addr, "127.0.0.1:") || strings.HasPrefix(addr, "localhost:") {
+		return "http://" + addr
+	}
+	if strings.HasPrefix(addr, "0.0.0.0:") || strings.HasPrefix(addr, "[::]:") {
+		if _, port, ok := strings.Cut(addr, ":"); ok {
+			return "http://127.0.0.1:" + port
+		}
+	}
+	return "http://" + addr
+}
+
+func usage() {
+	fmt.Print(`果果剧库 - 红果点播与下载工具
+
+请仅下载你拥有权利或已获授权的视频内容。
+
+用法：
+  直接执行 go run . 或编译后的程序，默认启动浏览器管理界面
+
+常用参数：
+  -ui=true|false               启动/关闭本地浏览器管理界面，默认 true
+  -listen 地址                UI 监听地址，默认 0.0.0.0:8999，支持局域网访问
+  -open=true|false            UI 模式是否自动打开浏览器，默认 true
+  -admin-user 用户名           管理员账号，首次默认 admin
+  -admin-password 密码         指定管理员密码；首次未指定时随机生成并输出，首次登录须修改
+  -mode all|search|id|list    CLI 模式，需配合 -ui=false，默认 all
+  -keyword 关键词             search 模式关键词
+  -id 剧ID                    id 模式下载单部剧
+  -out 目录                   自定义下载目录，默认 ./短剧下载，支持相对或绝对路径
+  -c 并发数                   下载并发，默认 2，可在界面设置中修改
+  -pages 页数                 每频道扫描页数；红果为 App 每批页数，默认 20
+  -data-dir 目录              配置、缓存和任务目录，默认 ./data
+  -config 文件                首次运行时导入旧版配置（可选）
+  -ffmpeg 路径                ffmpeg 路径，默认从 PATH 查找
+  -refresh                   CLI 模式强制更新剧库，默认读取本地缓存
+  -more                      CLI 模式从保存的红果 App 分页位置继续加载
+  -insecure-tls=true|false    是否跳过 TLS 证书校验，默认 false
+
+示例：
+  juku
+  juku -open=false
+  juku -ui=false -mode all
+  juku -ui=false -mode search -keyword 女总裁
+  juku -ui=false -mode id -id hongguo:7670772535931178008
+  juku -ui=false -mode list
+`)
+}
+
+func Run() {
+	mode := flag.String("mode", "all", "all/search/id/list")
+	keyword := flag.String("keyword", "", "search keyword")
+	id := flag.String("id", "", "drama id")
+	out := flag.String("out", "", "output directory")
+	concurrency := flag.Int("c", 0, "download concurrency")
+	pages := flag.Int("pages", 0, "max pages per sort")
+	configFile := flag.String("config", "", "import a legacy config on first startup")
+	dataDir := flag.String("data-dir", "data", "configuration, cache and task directory")
+	ffmpeg := flag.String("ffmpeg", "", "ffmpeg path")
+	adminUser := flag.String("admin-user", "", "administrator username, default admin on first startup")
+	adminPassword := flag.String("admin-password", "", "administrator password; default random on first startup")
+	uiMode := flag.Bool("ui", true, "start local web UI")
+	listen := flag.String("listen", defaultUIListenAddress, "UI listen address; use 127.0.0.1:8999 for local-only access")
+	open := flag.Bool("open", true, "open browser automatically in UI mode")
+	refresh := flag.Bool("refresh", false, "refresh the CLI library instead of using local cache")
+	more := flag.Bool("more", false, "continue loading the Hongguo App catalog from its saved cursor")
+	var insecureTLS boolOverride
+	flag.Var(&insecureTLS, "insecure-tls", "skip TLS certificate verification")
+	help := flag.Bool("help", false, "show help")
+	flag.Parse()
+	if *help {
+		usage()
+		return
+	}
+	if *refresh && *more {
+		fmt.Fprintln(os.Stderr, "-refresh 和 -more 不能同时使用")
+		os.Exit(2)
+	}
+
+	if !flagWasSet("data-dir") && !flagWasSet("config") {
+		if err := preparePortableWorkingDirectory(); err != nil {
+			fmt.Fprintln(os.Stderr, "初始化程序目录失败:", err)
+			os.Exit(1)
+		}
+	}
+	cfg, configErr := loadApplicationConfig(*dataDir, *configFile, *out)
+	if configErr != nil {
+		fmt.Fprintln(os.Stderr, "初始化配置失败:", publicError(configErr))
+		os.Exit(2)
+	}
+	cfg.adminUsername = firstNonEmpty(*adminUser, os.Getenv("JUKU_ADMIN_USER"), "admin")
+	cfg.adminUserExplicit = flagWasSet("admin-user") || os.Getenv("JUKU_ADMIN_USER") != ""
+	cfg.adminPassword = os.Getenv("JUKU_ADMIN_PASSWORD")
+	if flagWasSet("admin-password") {
+		cfg.adminPassword = *adminPassword
+	}
+	cfg.adminPasswordExplicit = flagWasSet("admin-password") || os.Getenv("JUKU_ADMIN_PASSWORD") != ""
+	if *concurrency > 0 {
+		cfg.Concurrency = *concurrency
+	}
+	if *pages > 0 {
+		cfg.MaxPagesPerSort = *pages
+	}
+	if *ffmpeg != "" {
+		cfg.FFmpeg = *ffmpeg
+	}
+	if insecureTLS.set {
+		cfg.InsecureTLS = insecureTLS.val
+	}
+	if err := cfg.validate(); err != nil {
+		fmt.Fprintf(os.Stderr, "配置错误: %v\n", err)
+		os.Exit(2)
+	}
+	d := NewDownloader(cfg)
+	cfg = d.cfg
+	if err := os.MkdirAll(cfg.OutputDir, 0o755); err != nil {
+		fmt.Fprintf(os.Stderr, "创建输出目录失败: %v\n", err)
+		os.Exit(1)
+	}
+	_, ffmpegErr := exec.LookPath(portableFFmpeg(cfg.FFmpeg))
+	fmt.Printf("输出目录: %s\n下载并发: %d\nFFmpeg 已找到（后台校验）: %t\nTLS证书校验: %t\n", cfg.OutputDir, cfg.Concurrency, ffmpegErr == nil, !cfg.InsecureTLS)
+	d.recordDiagnostic(diagnosticEvent{Level: "info", Event: "app.started", Message: "果果剧库已启动"})
+	fmt.Printf("诊断日志: %s\n", d.diagnostics.path)
+	if ffmpegErr != nil {
+		if automaticFFmpeg(cfg.FFmpeg) {
+			fmt.Println("未找到 FFmpeg，将自动下载匹配当前系统的便携版本；如下载失败，请在界面中调整代理后重试。")
+		} else {
+			fmt.Println("指定的 FFmpeg 路径未找到，请更正 download.ffmpeg 或 -ffmpeg。")
+		}
+	}
+
+	if *uiMode {
+		addr := normalizeListen(*listen)
+		app := NewUIApp(d)
+		pageURL := publicURL(addr)
+		fmt.Printf("监听地址: %s | 管理界面已启动: %s\n", addr, pageURL)
+		if *open {
+			go func() {
+				time.Sleep(500 * time.Millisecond)
+				openBrowser(pageURL)
+			}()
+		}
+		if err := app.ListenAndServe(addr); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			d.recordDiagnostic(diagnosticEvent{Event: "app.failed", Message: err.Error()})
+			fmt.Fprintf(os.Stderr, "UI 服务停止: %v\n", err)
+			os.Exit(1)
+		}
+		return
+	}
+
+	ctx := context.Background()
+	var dramas []Drama
+	var err error
+	switch strings.ToLower(*mode) {
+	case "id":
+		if strings.TrimSpace(*id) == "" {
+			fmt.Fprintln(os.Stderr, "-mode id 需要 -id")
+			os.Exit(2)
+		}
+		dramas = []Drama{{ID: strings.TrimSpace(*id), Title: "短剧"}}
+	case "all", "search", "list":
+		if *more {
+			dramas, err = d.RefreshDramas(context.WithValue(ctx, libraryMoreKey{}, true), sourceHongguo)
+		} else if *refresh {
+			dramas, err = d.RefreshDramas(ctx, "")
+		} else {
+			dramas, err = d.GetAllDramas(ctx)
+		}
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "  剧库部分来源失败，继续处理已获取的 %d 部：%v\n", len(dramas), err)
+			if len(dramas) == 0 {
+				os.Exit(1)
+			}
+		}
+		if strings.ToLower(*mode) == "search" {
+			kw := strings.TrimSpace(*keyword)
+			if kw == "" {
+				fmt.Fprintln(os.Stderr, "-mode search 需要 -keyword")
+				os.Exit(2)
+			}
+			var filtered []Drama
+			for _, dr := range dramas {
+				text := dr.DisplayTitle() + " " + dr.Desc + " " + dr.Intro + " " + dr.ChannelName
+				if strings.Contains(strings.ToLower(text), strings.ToLower(kw)) {
+					filtered = append(filtered, dr)
+				}
+			}
+			dramas = filtered
+			fmt.Printf(" 搜索命中：%d 部\n", len(dramas))
+		}
+		if strings.ToLower(*mode) == "list" {
+			for i, dr := range dramas {
+				fmt.Printf("%04d  [%s] %s  %s\n", i+1, dr.ChannelName, dr.ID, dr.DisplayTitle())
+			}
+			return
+		}
+	default:
+		usage()
+		os.Exit(2)
+	}
+	if len(dramas) == 0 {
+		fmt.Println("没有待下载短剧。")
+		return
+	}
+
+	var tasks []Task
+	for i, dr := range dramas {
+		fmt.Printf(" [%d/%d] 获取章节：《%s》 %s\n", i+1, len(dramas), dr.DisplayTitle(), dr.ID)
+		dramaTasks, err := d.BuildDramaTasks(ctx, dr)
+		if err != nil {
+			fmt.Printf("  获取章节失败：《%s》 %v\n", dr.DisplayTitle(), err)
+			continue
+		}
+		tasks = append(tasks, dramaTasks...)
+	}
+	fmt.Printf(" 待处理视频：%d 集\n", len(tasks))
+	results := DownloadTasks(ctx, d, tasks)
+	var ok, fail int
+	for _, r := range results {
+		if r.OK {
+			ok++
+		} else {
+			fail++
+		}
+	}
+	if err := saveFailures(cfg.dataDirectory(), results); err != nil {
+		fmt.Printf("  写入 failed.json 失败: %v\n", err)
+	}
+	fmt.Printf("\n 完成：成功/跳过 %d，失败 %d\n", ok, fail)
+	if fail > 0 {
+		fmt.Printf("失败详情已写入：%s\n", filepath.Join(cfg.dataDirectory(), "failed.json"))
+		os.Exit(1)
+	}
+}
diff --git a/internal/app/config_defaults.go b/internal/app/config_defaults.go
new file mode 100644
index 0000000..3ccb3b5
--- /dev/null
+++ b/internal/app/config_defaults.go
@@ -0,0 +1,63 @@
+package app
+
+import (
+	"errors"
+	"os"
+)
+
+const userAgent = "Mozilla/5.0 (iPhone; CPU iPhone OS 18_7 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/26.6 Mobile/15E148 Safari/604.1"
+
+type Config struct {
+	adminUsername         string
+	adminPassword         string
+	adminUserExplicit     bool
+	adminPasswordExplicit bool
+	settingsLoaded        bool
+	dataDir               string
+	outputDirSetting      string
+	OutputDir             string `json:"outputDir"`
+	GroupBySource         bool   `json:"groupBySource"`
+	FFmpeg                string `json:"ffmpeg"`
+	Concurrency           int    `json:"concurrency"`
+	RequestConcurrency    int    `json:"requestConcurrency"`
+	RequestIntervalMS     int    `json:"requestIntervalMs"`
+	MaxPagesPerSort       int    `json:"maxPagesPerSort"`
+	Retries               int    `json:"retries"`
+	SkipBytes             int64  `json:"skipBytes"`
+	InsecureTLS           bool   `json:"insecureTLS"`
+	ProxyURL              string `json:"proxyURL,omitempty"`
+	HongguoURL            string `json:"hongguoURL,omitempty"`
+}
+
+func defaultConfig() Config {
+	return Config{
+		OutputDir: defaultOutputDir(), FFmpeg: "ffmpeg", Concurrency: 2,
+		RequestConcurrency: 2, RequestIntervalMS: 500, MaxPagesPerSort: 50,
+		Retries: 3, SkipBytes: 512 * 1024,
+	}
+}
+
+func defaultOutputDir() string { return "短剧下载" }
+
+func applyConfigEnvironment(config *Config) {
+	for variable, target := range map[string]*string{
+		"JUKU_HONGGUO_URL": &config.HongguoURL,
+		"JUKU_PROXY_URL":   &config.ProxyURL,
+		"JUKU_OUTPUT_DIR":  &config.OutputDir,
+		"JUKU_FFMPEG":      &config.FFmpeg,
+	} {
+		if value := os.Getenv(variable); value != "" {
+			*target = value
+		}
+	}
+}
+
+func (config Config) validate() error {
+	if _, err := configuredProxy(config.ProxyURL); err != nil {
+		return err
+	}
+	if config.HongguoURL != "" && !isProviderHTTPMediaURL(config.HongguoURL) {
+		return errors.New("红果站点地址必须是有效的 HTTP/HTTPS URL")
+	}
+	return nil
+}
diff --git a/internal/app/config_runtime.go b/internal/app/config_runtime.go
new file mode 100644
index 0000000..3b27b27
--- /dev/null
+++ b/internal/app/config_runtime.go
@@ -0,0 +1,187 @@
+package app
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+type runtimeSettings struct {
+	Concurrency        int     `json:"concurrency"`
+	RequestConcurrency int     `json:"requestConcurrency"`
+	RequestIntervalMS  int     `json:"requestIntervalMs"`
+	ProxyURL           *string `json:"proxyURL,omitempty"`
+	OutputDir          *string `json:"outputDir,omitempty"`
+	GroupBySource      *bool   `json:"groupBySource,omitempty"`
+}
+
+func (settings runtimeSettings) validate() error {
+	if settings.OutputDir != nil {
+		if _, err := normalizedOutputDirectory(*settings.OutputDir); err != nil {
+			return err
+		}
+	}
+	if settings.ProxyURL != nil {
+		if _, err := configuredProxy(*settings.ProxyURL); err != nil {
+			return err
+		}
+	}
+	if settings.Concurrency < 1 || settings.Concurrency > 32 {
+		return errors.New("下载并发范围为 1–32")
+	}
+	if settings.RequestConcurrency < 1 || settings.RequestConcurrency > 16 {
+		return errors.New("剧库请求并发范围为 1–16")
+	}
+	if settings.RequestIntervalMS < 100 || settings.RequestIntervalMS > 60000 {
+		return errors.New("同站请求间隔范围为 100–60000 毫秒")
+	}
+	return nil
+}
+
+func runtimeSettingsPath(directory string) string {
+	return filepath.Join(directory, "juku.json")
+}
+
+func loadRuntimeSettings(cfg *Config) {
+	if cfg.settingsLoaded {
+		return
+	}
+	cfg.settingsLoaded = true
+	document, err := readConfigDocument(runtimeSettingsPath(cfg.runtimeSettingsDirectory()))
+	if err == nil {
+		loaded, configErr := document.config()
+		if configErr == nil {
+			loaded.dataDir = cfg.dataDirectory()
+			loaded.settingsLoaded = true
+			*cfg = loaded
+		}
+		return
+	}
+	if !errors.Is(err, os.ErrNotExist) {
+		fmt.Printf("配置读取失败，保留当前设置: %v\n", err)
+		return
+	}
+	body, err := os.ReadFile(filepath.Join(cfg.OutputDir, "settings.json"))
+	if errors.Is(err, os.ErrNotExist) {
+		return
+	}
+	var settings runtimeSettings
+	if err == nil {
+		err = json.Unmarshal(body, &settings)
+	}
+	if err == nil {
+		err = settings.validate()
+	}
+	if err != nil {
+		fmt.Printf("  界面并发设置读取失败，使用配置文件/默认值: %v\n", err)
+		return
+	}
+	applyRuntimeSettings(cfg, settings)
+}
+
+func applyRuntimeSettings(cfg *Config, settings runtimeSettings) {
+	cfg.Concurrency = settings.Concurrency
+	cfg.RequestConcurrency = settings.RequestConcurrency
+	cfg.RequestIntervalMS = settings.RequestIntervalMS
+	if settings.ProxyURL != nil {
+		cfg.ProxyURL = *settings.ProxyURL
+	}
+	if settings.OutputDir != nil {
+		cfg.OutputDir, _ = normalizedOutputDirectory(*settings.OutputDir)
+	}
+	if settings.GroupBySource != nil {
+		cfg.GroupBySource = *settings.GroupBySource
+	}
+}
+
+func (a *UIApp) updateRuntimeSettings(writer http.ResponseWriter, request *http.Request) bool {
+	var settings runtimeSettings
+	decoder := json.NewDecoder(http.MaxBytesReader(writer, request.Body, 4096))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(&settings); err != nil {
+		writeJSON(writer, http.StatusBadRequest, map[string]string{"error": "无效的并发设置"})
+		return false
+	}
+	if err := settings.validate(); err != nil {
+		writeJSON(writer, http.StatusBadRequest, map[string]string{"error": err.Error()})
+		return false
+	}
+	a.settingsMu.Lock()
+	defer a.settingsMu.Unlock()
+	a.mu.Lock()
+	cfg := a.cfg
+	if settings.ProxyURL == nil {
+		value := a.cfg.ProxyURL
+		settings.ProxyURL = &value
+	}
+	if settings.OutputDir == nil {
+		value := firstNonEmpty(a.nextOutputDir, cfg.outputDirSetting, cfg.OutputDir)
+		settings.OutputDir = &value
+	}
+	if settings.GroupBySource == nil {
+		value := cfg.GroupBySource
+		settings.GroupBySource = &value
+	}
+	a.mu.Unlock()
+	directory, err := normalizedOutputDirectory(*settings.OutputDir)
+	if err != nil {
+		writeJSON(writer, http.StatusBadRequest, map[string]string{"error": err.Error()})
+		return false
+	}
+	settings.OutputDir = &directory
+	if !sameDirectory(directory, cfg.OutputDir) {
+		if err := checkOutputDirectory(directory); err != nil {
+			writeJSON(writer, http.StatusBadRequest, map[string]string{"error": a.redactError(err)})
+			return false
+		}
+	}
+	if err := saveRuntimeSettings(cfg.runtimeSettingsDirectory(), settings); err != nil {
+		writeJSON(writer, http.StatusInternalServerError, map[string]string{"error": "设置保存失败: " + a.redactError(err)})
+		return false
+	}
+	a.downloader.proxyRouter.configure(*settings.ProxyURL)
+	a.downloader.client.CloseIdleConnections()
+	a.mu.Lock()
+	a.cfg.Concurrency = settings.Concurrency
+	a.cfg.RequestConcurrency = settings.RequestConcurrency
+	a.cfg.RequestIntervalMS = settings.RequestIntervalMS
+	a.cfg.ProxyURL = *settings.ProxyURL
+	a.cfg.GroupBySource = *settings.GroupBySource
+	a.downloader.directoryMu.Lock()
+	a.downloader.downloadGrouping = settings.GroupBySource
+	a.downloader.directoryMu.Unlock()
+	a.nextOutputDir = directory
+	a.downloader.limiter.configure(settings.RequestConcurrency, time.Duration(settings.RequestIntervalMS)*time.Millisecond)
+	a.ensureWorkersLocked()
+	a.cond.Broadcast()
+	a.mu.Unlock()
+	return true
+}
+
+func saveRuntimeSettings(directory string, settings runtimeSettings) error {
+	if err := settings.validate(); err != nil {
+		return err
+	}
+	path := runtimeSettingsPath(directory)
+	document, err := readConfigDocument(path)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	document.Download.Concurrency = settings.Concurrency
+	document.Network.RequestConcurrency = settings.RequestConcurrency
+	document.Network.RequestIntervalMS = settings.RequestIntervalMS
+	if settings.OutputDir != nil {
+		document.Download.Directory = *settings.OutputDir
+	}
+	if settings.GroupBySource != nil {
+		document.Download.GroupBySource = *settings.GroupBySource
+	}
+	if settings.ProxyURL != nil {
+		document.Network.Proxy = *settings.ProxyURL
+	}
+	return writeConfigDocument(path, document)
+}
diff --git a/internal/app/config_store.go b/internal/app/config_store.go
new file mode 100644
index 0000000..f8ab490
--- /dev/null
+++ b/internal/app/config_store.go
@@ -0,0 +1,308 @@
+package app
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+type configDocument struct {
+	Version  int               `json:"version"`
+	Download downloadSettings  `json:"download"`
+	Network  networkSettings   `json:"network"`
+	Sources  *sourceSettings   `json:"sources,omitempty"`
+	Advanced *advancedSettings `json:"advanced,omitempty"`
+}
+
+type downloadSettings struct {
+	Directory     string `json:"directory"`
+	GroupBySource bool   `json:"groupBySource,omitempty"`
+	Concurrency   int    `json:"concurrency"`
+	FFmpeg        string `json:"ffmpeg,omitempty"`
+}
+
+type networkSettings struct {
+	Proxy              string `json:"proxy"`
+	RequestConcurrency int    `json:"requestConcurrency"`
+	RequestIntervalMS  int    `json:"requestIntervalMs"`
+}
+
+type sourceSettings struct {
+	Hongguo *siteSettings `json:"hongguo,omitempty"`
+}
+
+type siteSettings struct {
+	BaseURL string `json:"baseURL,omitempty"`
+}
+
+type advancedSettings struct {
+	MaxPagesPerSort int   `json:"maxPagesPerSort,omitempty"`
+	Retries         int   `json:"retries,omitempty"`
+	SkipBytes       int64 `json:"skipBytes,omitempty"`
+	InsecureTLS     bool  `json:"insecureTLS,omitempty"`
+}
+
+func documentFromConfig(cfg Config) configDocument {
+	defaults := defaultConfig()
+	document := configDocument{
+		Version:  1,
+		Download: downloadSettings{Directory: firstNonEmpty(cfg.outputDirSetting, cfg.OutputDir), GroupBySource: cfg.GroupBySource, Concurrency: cfg.Concurrency},
+		Network:  networkSettings{Proxy: firstNonEmpty(cfg.ProxyURL, "auto"), RequestConcurrency: cfg.RequestConcurrency, RequestIntervalMS: cfg.RequestIntervalMS},
+	}
+	if cfg.FFmpeg != "" && cfg.FFmpeg != defaults.FFmpeg {
+		document.Download.FFmpeg = cfg.FFmpeg
+	}
+	sources := sourceSettings{}
+	if cfg.HongguoURL != "" {
+		sources.Hongguo = &siteSettings{BaseURL: cfg.HongguoURL}
+	}
+	if sources.Hongguo != nil {
+		document.Sources = &sources
+	}
+	advanced := advancedSettings{InsecureTLS: cfg.InsecureTLS}
+	if cfg.MaxPagesPerSort != defaults.MaxPagesPerSort {
+		advanced.MaxPagesPerSort = cfg.MaxPagesPerSort
+	}
+	if cfg.Retries != defaults.Retries {
+		advanced.Retries = cfg.Retries
+	}
+	if cfg.SkipBytes != defaults.SkipBytes {
+		advanced.SkipBytes = cfg.SkipBytes
+	}
+	if advanced != (advancedSettings{}) {
+		document.Advanced = &advanced
+	}
+	return document
+}
+
+func (document configDocument) config() (Config, error) {
+	if document.Version != 1 {
+		return Config{}, fmt.Errorf("不支持的配置版本 %d，请使用兼容的程序版本", document.Version)
+	}
+	cfg := defaultConfig()
+	cfg.OutputDir = document.Download.Directory
+	cfg.GroupBySource = document.Download.GroupBySource
+	cfg.Concurrency = document.Download.Concurrency
+	cfg.FFmpeg = firstNonEmpty(document.Download.FFmpeg, cfg.FFmpeg)
+	cfg.ProxyURL = document.Network.Proxy
+	cfg.RequestConcurrency = document.Network.RequestConcurrency
+	cfg.RequestIntervalMS = document.Network.RequestIntervalMS
+	if sources := document.Sources; sources != nil {
+		if sources.Hongguo != nil {
+			cfg.HongguoURL = sources.Hongguo.BaseURL
+		}
+	}
+	if advanced := document.Advanced; advanced != nil {
+		if advanced.MaxPagesPerSort > 0 {
+			cfg.MaxPagesPerSort = advanced.MaxPagesPerSort
+		}
+		if advanced.Retries > 0 {
+			cfg.Retries = advanced.Retries
+		}
+		if advanced.SkipBytes > 0 {
+			cfg.SkipBytes = advanced.SkipBytes
+		}
+		cfg.InsecureTLS = advanced.InsecureTLS
+	}
+	settings := runtimeSettings{Concurrency: cfg.Concurrency, RequestConcurrency: cfg.RequestConcurrency, RequestIntervalMS: cfg.RequestIntervalMS, ProxyURL: &cfg.ProxyURL, OutputDir: &cfg.OutputDir}
+	if err := settings.validate(); err != nil {
+		return Config{}, err
+	}
+	if err := cfg.validate(); err != nil {
+		return Config{}, err
+	}
+	return cfg, nil
+}
+
+func readConfigDocument(path string) (configDocument, error) {
+	document := documentFromConfig(defaultConfig())
+	file, err := os.Open(path)
+	if err != nil {
+		return document, err
+	}
+	defer file.Close()
+	info, err := file.Stat()
+	if err != nil {
+		return document, err
+	}
+	if info.Size() > 1<<20 {
+		return document, errors.New("配置文件超过 1 MB")
+	}
+	decoder := json.NewDecoder(io.LimitReader(file, (1<<20)+1))
+	content := &document
+	if err := decoder.Decode(&content); err != nil {
+		return document, fmt.Errorf("配置文件格式无效: %w", err)
+	}
+	if content == nil {
+		return document, errors.New("配置文件必须是 JSON 对象")
+	}
+	if err := decoder.Decode(new(any)); !errors.Is(err, io.EOF) {
+		return document, errors.New("配置文件含有多余内容")
+	}
+	if _, err := document.config(); err != nil {
+		return document, err
+	}
+	return document, nil
+}
+
+func writeConfigDocument(path string, document configDocument) error {
+	if _, err := document.config(); err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return err
+	}
+	file, err := os.CreateTemp(filepath.Dir(path), ".config-*.tmp")
+	if err != nil {
+		return err
+	}
+	defer os.Remove(file.Name())
+	encoder := json.NewEncoder(file)
+	encoder.SetIndent("", "  ")
+	err = encoder.Encode(document)
+	if err == nil {
+		err = file.Sync()
+	}
+	closeErr := file.Close()
+	if err != nil {
+		return err
+	}
+	if closeErr != nil {
+		return closeErr
+	}
+	return os.Rename(file.Name(), path)
+}
+
+func loadApplicationConfig(dataDirectory, importPath, outputOverride string) (Config, error) {
+	dataDirectory, err := filepath.Abs(dataDirectory)
+	if err != nil {
+		return Config{}, err
+	}
+	path := runtimeSettingsPath(dataDirectory)
+	document, err := readConfigDocument(path)
+	if errors.Is(err, os.ErrNotExist) {
+		cfg, legacyDirectories, importErr := importLegacyConfig(firstNonEmpty(importPath, "config.json"), outputOverride)
+		if importErr != nil {
+			return Config{}, importErr
+		}
+		document = documentFromConfig(cfg)
+		if _, err := document.config(); err != nil {
+			return Config{}, err
+		}
+		if err := migrateLegacyData(dataDirectory, legacyDirectories); err != nil {
+			return Config{}, err
+		}
+		if err := writeConfigDocument(path, document); err != nil {
+			return Config{}, fmt.Errorf("首次生成配置失败: %w", err)
+		}
+	} else if err != nil {
+		return Config{}, fmt.Errorf("无法读取 %s，原文件未修改: %w", path, err)
+	}
+	cfg, err := document.config()
+	if err != nil {
+		return Config{}, err
+	}
+	cfg.settingsLoaded = true
+	cfg.dataDir = dataDirectory
+	applyConfigEnvironment(&cfg)
+	if outputOverride != "" {
+		cfg.OutputDir = outputOverride
+	}
+	return cfg, nil
+}
+
+func importLegacyConfig(path, outputOverride string) (Config, []string, error) {
+	cfg := defaultConfig()
+	body, err := os.ReadFile(path)
+	if err == nil {
+		if err := json.Unmarshal(body, &cfg); err != nil {
+			return cfg, nil, fmt.Errorf("旧配置格式错误，未覆盖原文件: %w", err)
+		}
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return cfg, nil, err
+	}
+	if cfg.OutputDir == "" {
+		cfg.OutputDir = defaultOutputDir()
+	}
+	if cfg.RequestConcurrency <= 0 {
+		cfg.RequestConcurrency = 2
+	}
+	if cfg.RequestIntervalMS <= 0 {
+		cfg.RequestIntervalMS = 500
+	}
+	directories := []string{firstNonEmpty(outputOverride, cfg.OutputDir), cfg.OutputDir}
+	candidates := []string{filepath.Join(filepath.Dir(path), "juku-settings.json")}
+	for _, directory := range directories {
+		candidates = append(candidates, filepath.Join(directory, "settings.json"))
+	}
+	for _, candidate := range candidates {
+		body, err = os.ReadFile(candidate)
+		if errors.Is(err, os.ErrNotExist) {
+			continue
+		}
+		if err != nil {
+			return cfg, nil, err
+		}
+		var settings runtimeSettings
+		if err := json.Unmarshal(body, &settings); err != nil {
+			return cfg, nil, fmt.Errorf("旧设置格式错误: %w", err)
+		}
+		if err := settings.validate(); err != nil {
+			return cfg, nil, err
+		}
+		applyRuntimeSettings(&cfg, settings)
+		break
+	}
+	return cfg, append(directories, cfg.OutputDir, filepath.Dir(path)), nil
+}
+
+func migrateLegacyData(directory string, candidates []string) error {
+	if err := os.MkdirAll(directory, 0o755); err != nil {
+		return err
+	}
+	for _, name := range []string{"library.json", "ui-state.json", "failed.json"} {
+		target := filepath.Join(directory, name)
+		if _, err := os.Stat(target); err == nil {
+			continue
+		} else if !errors.Is(err, os.ErrNotExist) {
+			return err
+		}
+		for _, candidate := range candidates {
+			if sameDirectory(directory, candidate) {
+				continue
+			}
+			original := filepath.Join(candidate, name)
+			body, err := os.ReadFile(original)
+			if errors.Is(err, os.ErrNotExist) {
+				continue
+			}
+			if err != nil {
+				return err
+			}
+			if !json.Valid(body) {
+				return fmt.Errorf("旧数据 %s 格式无效，原文件未修改", original)
+			}
+			file, err := os.OpenFile(target, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
+			if errors.Is(err, os.ErrExist) {
+				break
+			}
+			if err != nil {
+				return err
+			}
+			_, err = file.Write(body)
+			if err == nil {
+				err = file.Sync()
+			}
+			closeErr := file.Close()
+			if err != nil || closeErr != nil {
+				_ = os.Remove(target)
+				return errors.Join(err, closeErr)
+			}
+			break
+		}
+	}
+	return nil
+}
diff --git a/internal/app/desktop_picker.go b/internal/app/desktop_picker.go
new file mode 100644
index 0000000..f5b565b
--- /dev/null
+++ b/internal/app/desktop_picker.go
@@ -0,0 +1,226 @@
+package app
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"mime"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"time"
+	"unicode/utf16"
+)
+
+const macDirectoryPickerScript = `ObjC.import('AppKit');
+function run(arguments) {
+  var application = $.NSApplication.sharedApplication;
+  application.setActivationPolicy($.NSApplicationActivationPolicyAccessory);
+  var panel = $.NSOpenPanel.openPanel;
+  panel.setTitle('选择下载文件夹');
+  panel.setPrompt('选择');
+  panel.setCanChooseFiles(false);
+  panel.setCanChooseDirectories(true);
+  panel.setAllowsMultipleSelection(false);
+  panel.setCanCreateDirectories(true);
+  panel.setDirectoryURL($.NSURL.fileURLWithPath(arguments[0]));
+  application.activateIgnoringOtherApps(true);
+  return panel.runModal === $.NSModalResponseOK ? ObjC.unwrap(panel.URL.path) : '';
+}`
+
+const windowsDirectoryPickerScript = `$ErrorActionPreference = 'Stop'
+[Console]::OutputEncoding = New-Object System.Text.UTF8Encoding($false)
+Add-Type -AssemblyName System.Windows.Forms
+[System.Windows.Forms.Application]::EnableVisualStyles()
+$dialog = New-Object System.Windows.Forms.FolderBrowserDialog
+$owner = New-Object System.Windows.Forms.Form
+try {
+  $dialog.Description = '选择下载文件夹'
+  $dialog.ShowNewFolderButton = $true
+  $dialog.SelectedPath = $env:JUKU_PICKER_START_DIRECTORY
+  $owner.ShowInTaskbar = $false
+  $owner.TopMost = $true
+  $owner.Opacity = 0
+  $owner.Show()
+  $owner.Activate()
+  if ($dialog.ShowDialog($owner) -eq [System.Windows.Forms.DialogResult]::OK) {
+    [Console]::Write($dialog.SelectedPath)
+  }
+} finally {
+  $dialog.Dispose()
+  $owner.Dispose()
+}`
+
+var configureDirectoryPickerProcess = func(command *exec.Cmd) {}
+
+func directoryPickerCommand(ctx context.Context, system, initial string) (*exec.Cmd, bool, error) {
+	var command *exec.Cmd
+	cancelExit := false
+	switch system {
+	case "darwin":
+		command = exec.CommandContext(ctx, "osascript", "-l", "JavaScript", "-e", macDirectoryPickerScript, initial)
+	case "windows":
+		encoded := utf16.Encode([]rune(windowsDirectoryPickerScript))
+		body := make([]byte, len(encoded)*2)
+		for index, value := range encoded {
+			body[index*2], body[index*2+1] = byte(value), byte(value>>8)
+		}
+		command = exec.CommandContext(ctx, "powershell.exe", "-NoLogo", "-NoProfile", "-NonInteractive", "-STA", "-EncodedCommand", base64.StdEncoding.EncodeToString(body))
+		command.Env = append(os.Environ(), "JUKU_PICKER_START_DIRECTORY="+initial)
+	case "linux":
+		if os.Getenv("DISPLAY") == "" && os.Getenv("WAYLAND_DISPLAY") == "" {
+			return nil, false, errors.New("当前没有桌面会话，请手动输入下载路径")
+		}
+		if executable, err := exec.LookPath("zenity"); err == nil {
+			command = exec.CommandContext(ctx, executable, "--file-selection", "--directory", "--title=选择下载文件夹", "--filename="+initial+string(os.PathSeparator))
+		} else if executable, err := exec.LookPath("kdialog"); err == nil {
+			command = exec.CommandContext(ctx, executable, "--getexistingdirectory", initial, "--title", "选择下载文件夹")
+		} else {
+			return nil, false, errors.New("当前桌面没有 zenity 或 kdialog，请安装其一或手动输入下载路径")
+		}
+		cancelExit = true
+	default:
+		return nil, false, errors.New("当前系统暂不支持原生文件夹选择，请手动输入下载路径")
+	}
+	configureDirectoryPickerProcess(command)
+	return command, cancelExit, nil
+}
+
+func nativeDirectoryPicker(ctx context.Context, initial string) (string, error) {
+	command, cancelExit, err := directoryPickerCommand(ctx, runtime.GOOS, initial)
+	if err != nil {
+		return "", err
+	}
+	output, err := command.Output()
+	if ctx.Err() != nil {
+		return "", ctx.Err()
+	}
+	if err != nil {
+		var exitError *exec.ExitError
+		if cancelExit && errors.As(err, &exitError) && exitError.ExitCode() == 1 && strings.TrimSpace(string(exitError.Stderr)) == "" {
+			return "", nil
+		}
+		return "", fmt.Errorf("系统文件夹选择框启动失败，请确认桌面会话可用，或手动输入路径: %w", err)
+	}
+	return strings.TrimRight(strings.TrimPrefix(string(output), "\ufeff"), "\r\n"), nil
+}
+
+func pickerInitialDirectory(initial, fallback string) string {
+	for _, candidate := range []string{initial, fallback, "."} {
+		if candidate == "" {
+			continue
+		}
+		absolute, err := filepath.Abs(candidate)
+		if err != nil {
+			continue
+		}
+		for {
+			if info, err := os.Stat(absolute); err == nil && info.IsDir() {
+				return absolute
+			}
+			parent := filepath.Dir(absolute)
+			if parent == absolute {
+				break
+			}
+			absolute = parent
+		}
+	}
+	return ""
+}
+
+func directorySelectionPath(absolute string) string {
+	if working, err := os.Getwd(); err == nil {
+		if relative, err := filepath.Rel(working, absolute); err == nil && relative != ".." && !strings.HasPrefix(relative, ".."+string(filepath.Separator)) && !filepath.IsAbs(relative) {
+			return relative
+		}
+	}
+	return absolute
+}
+
+func localDirectoryPickerRequest(request *http.Request) bool {
+	remote, _, err := net.SplitHostPort(request.RemoteAddr)
+	if err != nil || !net.ParseIP(remote).IsLoopback() {
+		return false
+	}
+	host := (&url.URL{Host: request.Host}).Hostname()
+	if !strings.EqualFold(host, "localhost") && !net.ParseIP(host).IsLoopback() {
+		return false
+	}
+	if site := request.Header.Get("Sec-Fetch-Site"); site != "" && site != "same-origin" && site != "none" {
+		return false
+	}
+	if origin := request.Header.Get("Origin"); origin != "" {
+		parsed, err := url.Parse(origin)
+		if err != nil || parsed.User != nil || parsed.Scheme != "http" && parsed.Scheme != "https" || !strings.EqualFold(parsed.Host, request.Host) {
+			return false
+		}
+	}
+	return true
+}
+
+func (a *UIApp) handleDirectoryPicker(writer http.ResponseWriter, request *http.Request) {
+	writer.Header().Set("Cache-Control", "no-store")
+	if request.Method != http.MethodPost {
+		writer.Header().Set("Allow", http.MethodPost)
+		writeJSON(writer, http.StatusMethodNotAllowed, map[string]string{"error": "method not allowed"})
+		return
+	}
+	if !localDirectoryPickerRequest(request) {
+		writeJSON(writer, http.StatusForbidden, map[string]string{"error": "请在运行程序的电脑上使用 localhost 或 127.0.0.1 打开界面；远程访问请手动输入服务器路径"})
+		return
+	}
+	contentType, _, _ := mime.ParseMediaType(request.Header.Get("Content-Type"))
+	if contentType != "application/json" {
+		writeJSON(writer, http.StatusUnsupportedMediaType, map[string]string{"error": "请求必须使用 JSON"})
+		return
+	}
+	var selection struct {
+		InitialPath string `json:"initialPath"`
+	}
+	decoder := json.NewDecoder(http.MaxBytesReader(writer, request.Body, 16384))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(&selection); err != nil || len(selection.InitialPath) > 8192 || strings.ContainsAny(selection.InitialPath, "\x00\r\n") {
+		writeJSON(writer, http.StatusBadRequest, map[string]string{"error": "无效的初始目录"})
+		return
+	}
+	if !a.directoryPickerMu.TryLock() {
+		writeJSON(writer, http.StatusConflict, map[string]string{"error": "系统文件夹选择框已打开，请先完成或取消选择"})
+		return
+	}
+	defer a.directoryPickerMu.Unlock()
+	a.mu.Lock()
+	output, picker := a.cfg.OutputDir, a.directoryPicker
+	a.mu.Unlock()
+	if picker == nil {
+		picker = nativeDirectoryPicker
+	}
+	ctx, cancel := context.WithTimeout(request.Context(), 5*time.Minute)
+	defer cancel()
+	path, err := picker(ctx, pickerInitialDirectory(selection.InitialPath, output))
+	if err != nil {
+		if errors.Is(err, context.DeadlineExceeded) {
+			writeJSON(writer, http.StatusGatewayTimeout, map[string]string{"error": "文件夹选择超时，请重试或手动输入路径"})
+		} else {
+			writeJSON(writer, http.StatusServiceUnavailable, map[string]string{"error": a.redactError(err)})
+		}
+		return
+	}
+	if path == "" {
+		writeJSON(writer, http.StatusOK, map[string]bool{"canceled": true})
+		return
+	}
+	info, err := os.Stat(path)
+	if err != nil || !filepath.IsAbs(path) || strings.ContainsAny(path, "\x00\r\n") || !info.IsDir() {
+		writeJSON(writer, http.StatusBadRequest, map[string]string{"error": "系统未返回有效文件夹，请重新选择"})
+		return
+	}
+	path = filepath.Clean(path)
+	writeJSON(writer, http.StatusOK, map[string]any{"path": path, "selectionPath": directorySelectionPath(path), "canceled": false})
+}
diff --git a/internal/app/desktop_picker_windows.go b/internal/app/desktop_picker_windows.go
new file mode 100644
index 0000000..4ad8e5b
--- /dev/null
+++ b/internal/app/desktop_picker_windows.go
@@ -0,0 +1,12 @@
+package app
+
+import (
+	"os/exec"
+	"syscall"
+)
+
+func init() {
+	configureDirectoryPickerProcess = func(command *exec.Cmd) {
+		command.SysProcAttr = &syscall.SysProcAttr{HideWindow: true, CreationFlags: 0x08000000}
+	}
+}
diff --git a/internal/app/diagnostics.go b/internal/app/diagnostics.go
new file mode 100644
index 0000000..e85bc7a
--- /dev/null
+++ b/internal/app/diagnostics.go
@@ -0,0 +1,120 @@
+package app
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"sync"
+	"time"
+)
+
+const diagnosticLogBytes = 5 * 1024 * 1024
+const diagnosticLogBackups = 2
+
+type diagnosticEvent struct {
+	HTTPStatus         int       `json:"httpStatus,omitempty"`
+	RequestedQuality   int       `json:"requestedQuality,omitempty"`
+	Time               time.Time `json:"time"`
+	Level              string    `json:"level"`
+	Event              string    `json:"event"`
+	Source             string    `json:"source,omitempty"`
+	DramaID            string    `json:"dramaId,omitempty"`
+	DramaTitle         string    `json:"dramaTitle,omitempty"`
+	Episode            int       `json:"episode,omitempty"`
+	Run                uint64    `json:"run,omitempty"`
+	StartSeconds       float64   `json:"startSeconds,omitempty"`
+	Host               string    `json:"host,omitempty"`
+	OffsetBytes        int64     `json:"offsetBytes,omitempty"`
+	TotalBytes         int64     `json:"totalBytes,omitempty"`
+	Attempt            int       `json:"attempt,omitempty"`
+	Quality            int       `json:"quality,omitempty"`
+	AvailableQualities []int     `json:"availableQualities,omitempty"`
+	Message            string    `json:"message"`
+}
+
+type diagnosticLog struct {
+	mu          sync.Mutex
+	path        string
+	limit       int64
+	warningOnce sync.Once
+}
+
+func newDiagnosticLog(directory string) *diagnosticLog {
+	return &diagnosticLog{path: filepath.Join(directory, "logs", "app.log"), limit: diagnosticLogBytes}
+}
+
+func (log *diagnosticLog) write(event diagnosticEvent) error {
+	event.Time = time.Now()
+	if event.Level == "" {
+		event.Level = "error"
+	}
+	data, err := json.Marshal(event)
+	if err != nil {
+		return err
+	}
+	data = append(data, '\n')
+	log.mu.Lock()
+	defer log.mu.Unlock()
+	if int64(len(data)) > log.limit {
+		return errors.New("单条诊断日志过大")
+	}
+	if err := os.MkdirAll(filepath.Dir(log.path), 0700); err != nil {
+		return err
+	}
+	info, err := os.Stat(log.path)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	if info != nil && info.Size()+int64(len(data)) > log.limit {
+		if err := log.rotate(); err != nil {
+			return err
+		}
+	}
+	file, err := os.OpenFile(log.path, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0600)
+	if err != nil {
+		return err
+	}
+	_, writeErr := file.Write(data)
+	return errors.Join(writeErr, file.Close())
+}
+
+func (log *diagnosticLog) rotate() error {
+	oldest := log.path + "." + strconv.Itoa(diagnosticLogBackups)
+	if err := os.Remove(oldest); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	for index := diagnosticLogBackups; index > 0; index-- {
+		previous := log.path
+		if index > 1 {
+			previous += "." + strconv.Itoa(index-1)
+		}
+		if err := os.Rename(previous, log.path+"."+strconv.Itoa(index)); err != nil && !errors.Is(err, os.ErrNotExist) {
+			return err
+		}
+	}
+	return nil
+}
+
+func (downloader *Downloader) recordDiagnostic(event diagnosticEvent) {
+	if downloader == nil || downloader.diagnostics == nil {
+		return
+	}
+	event.Message = truncate(redactErrorString(event.Message), 4096)
+	event.DramaTitle = truncate(redactErrorString(event.DramaTitle), 256)
+	if err := downloader.diagnostics.write(event); err != nil {
+		downloader.diagnostics.warningOnce.Do(func() {
+			fmt.Fprintf(os.Stderr, "诊断日志保存失败：%v\n", publicError(err))
+		})
+	}
+}
+
+func (downloader *Downloader) recordTaskFailure(event string, task Task, start float64, err error) {
+	if err == nil {
+		return
+	}
+	downloader.recordDiagnostic(diagnosticEvent{Event: event, Source: firstNonEmpty(task.Chapter.Source, sourceFromDramaID(task.DramaID)),
+		DramaID: task.DramaID, DramaTitle: task.DramaTitle, Episode: task.Index, StartSeconds: start, Message: err.Error()})
+}
diff --git a/internal/app/diagnostics_test.go b/internal/app/diagnostics_test.go
new file mode 100644
index 0000000..9c5a6ea
--- /dev/null
+++ b/internal/app/diagnostics_test.go
@@ -0,0 +1,137 @@
+package app
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"sync"
+	"testing"
+)
+
+func readDiagnosticEvents(t *testing.T, path string) []diagnosticEvent {
+	t.Helper()
+	file, err := os.Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+	var events []diagnosticEvent
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		var event diagnosticEvent
+		if err := json.Unmarshal(scanner.Bytes(), &event); err != nil || event.Time.IsZero() || event.Event == "" {
+			t.Fatal("invalid diagnostic record", err)
+		}
+		events = append(events, event)
+	}
+	if err := scanner.Err(); err != nil {
+		t.Fatal(err)
+	}
+	return events
+}
+
+func TestDiagnosticLogConcurrentWritesAndRedaction(t *testing.T) {
+	log := newDiagnosticLog(t.TempDir())
+	d := &Downloader{diagnostics: log}
+	var group sync.WaitGroup
+	for index := 0; index < 50; index++ {
+		group.Add(1)
+		go func(index int) {
+			defer group.Done()
+			d.recordDiagnostic(diagnosticEvent{Event: "fixture.failed", Episode: index + 1, Message: "https://user:fixture-password@media.invalid/video?token=fixture-token&key=fixture-media-key&signature=fixture-signature#fixture-fragment"})
+		}(index)
+	}
+	group.Wait()
+	events := readDiagnosticEvents(t, log.path)
+	seen := make(map[int]bool)
+	for _, event := range events {
+		seen[event.Episode] = true
+		for _, secret := range []string{"fixture-token", "fixture-media-key", "fixture-password", "fixture-signature", "fixture-fragment"} {
+			if strings.Contains(event.Message, secret) {
+				t.Fatal("diagnostic log exposed a credential or signed URL parameter")
+			}
+		}
+	}
+	if len(events) != 50 || len(seen) != 50 {
+		t.Fatal("concurrent diagnostic events were lost or interleaved")
+	}
+	info, err := os.Stat(log.path)
+	if err != nil || runtime.GOOS != "windows" && info.Mode().Perm()&0077 != 0 {
+		t.Fatal("new diagnostic file was not private", err)
+	}
+}
+
+func TestDiagnosticLogRotationBoundsFiles(t *testing.T) {
+	log := newDiagnosticLog(t.TempDir())
+	log.limit = 512
+	for index := 0; index < 30; index++ {
+		if err := log.write(diagnosticEvent{Event: "fixture.rotate", Episode: index, Message: strings.Repeat("x", 100)}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	files, err := os.ReadDir(filepath.Dir(log.path))
+	if err != nil || len(files) != diagnosticLogBackups+1 {
+		t.Fatal("diagnostic rotation exceeded its file bound", err)
+	}
+	for _, file := range files {
+		info, err := file.Info()
+		if err != nil || info.Size() > log.limit || len(readDiagnosticEvents(t, filepath.Join(filepath.Dir(log.path), file.Name()))) == 0 {
+			t.Fatal("rotation kept an oversized or invalid file", err)
+		}
+	}
+	current := readDiagnosticEvents(t, log.path)
+	if current[len(current)-1].Episode != 29 {
+		t.Fatal("rotation discarded the latest event")
+	}
+	if err := newDiagnosticLog(filepath.Dir(filepath.Dir(log.path))).write(diagnosticEvent{Event: "fixture.restart", Message: "restart"}); err != nil {
+		t.Fatal("reopening diagnostics failed", err)
+	}
+}
+
+func TestDiagnosticWriteFailureDoesNotReplacePlaybackError(t *testing.T) {
+	directory := t.TempDir()
+	if err := os.WriteFile(filepath.Join(directory, "logs"), []byte("keep"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	log := newDiagnosticLog(directory)
+	if err := log.write(diagnosticEvent{Event: "fixture.failed", Message: "failure"}); err == nil {
+		t.Fatal("unwritable diagnostics unexpectedly succeeded")
+	}
+	d := &Downloader{diagnostics: log}
+	d.recordTaskFailure("playback.failed", Task{}, 49, errors.New("unexpected EOF"))
+	data, err := os.ReadFile(filepath.Join(directory, "logs"))
+	if err != nil || string(data) != "keep" {
+		t.Fatal("diagnostics replaced an existing file", err)
+	}
+}
+
+func TestPlaybackFailureLogIncludesEpisodeAndSkipsStoppedRun(t *testing.T) {
+	app, session := prefetchFixtureApp(t)
+	session.tasks[0] = Task{DramaID: "hongguo:7000000000000000001", DramaTitle: "合成播放条目", Index: 1}
+	run, _, err := app.beginPlayback(viewerFixtureContext(app, context.Background()), "fixture", 1, 49, 0, 1, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer run.stop()
+	app.finishPlaybackRun(run, errors.New("unexpected EOF"), false)
+	app.finishPlaybackRun(run, context.Canceled, true)
+	events := readDiagnosticEvents(t, app.downloader.diagnostics.path)
+	failures := 0
+	for _, event := range events {
+		if event.Event == "playback.failed" {
+			failures++
+			if event.DramaID != run.task.DramaID || event.DramaTitle != run.task.DramaTitle || event.Episode != 1 || event.StartSeconds != 49 || event.Message != "unexpected EOF" {
+				t.Fatal("playback failure lost its diagnostic context", fmt.Sprint(event))
+			}
+		}
+	}
+	if failures != 1 {
+		t.Fatal("stopping playback generated a false diagnostic failure")
+	}
+}
diff --git a/internal/app/download_checkpoint.go b/internal/app/download_checkpoint.go
new file mode 100644
index 0000000..60213b5
--- /dev/null
+++ b/internal/app/download_checkpoint.go
@@ -0,0 +1,350 @@
+package app
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type downloadCheckpointState struct {
+	URL       string `json:"url"`
+	Validator string `json:"validator,omitempty"`
+	Total     int64  `json:"total,omitempty"`
+	Complete  bool   `json:"complete,omitempty"`
+}
+
+type downloadCheckpointRequest func(context.Context, int64, string) (*http.Request, error)
+type downloadCheckpointFetch func(*http.Request) (*http.Response, error)
+
+type downloadMediaCache struct {
+	directory string
+}
+
+func downloadHTTPValidator(header http.Header) string {
+	if value := strings.TrimSpace(header.Get("ETag")); value != "" && !strings.HasPrefix(value, "W/") {
+		return value
+	}
+	if value := strings.TrimSpace(header.Get("Last-Modified")); value != "" {
+		if _, err := http.ParseTime(value); err == nil {
+			return value
+		}
+	}
+	return ""
+}
+
+func readDownloadCheckpoint(path, address string) downloadCheckpointState {
+	var state downloadCheckpointState
+	body, err := os.ReadFile(path)
+	if err != nil || len(body) > 64<<10 || json.Unmarshal(body, &state) != nil || state.URL != address {
+		return downloadCheckpointState{}
+	}
+	return state
+}
+
+func writeDownloadCheckpoint(path string, state downloadCheckpointState) error {
+	body, err := json.Marshal(state)
+	if err != nil {
+		return err
+	}
+	if err = os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
+		return err
+	}
+	file, err := os.CreateTemp(filepath.Dir(path), ".download-checkpoint-*.tmp")
+	if err != nil {
+		return err
+	}
+	name := file.Name()
+	defer os.Remove(name)
+	if _, err = file.Write(body); err == nil {
+		err = file.Sync()
+	}
+	if closeErr := file.Close(); err == nil {
+		err = closeErr
+	}
+	if err != nil {
+		return err
+	}
+	return os.Rename(name, path)
+}
+
+func checkpointExistingComplete(path string, state downloadCheckpointState, key bool) (int64, bool) {
+	if !state.Complete {
+		return 0, false
+	}
+	info, err := os.Stat(path)
+	if err != nil || info.IsDir() || info.Size() <= 0 || state.Total > 0 && info.Size() != state.Total || key && info.Size() != 16 {
+		return 0, false
+	}
+	return info.Size(), true
+}
+
+func checkpointPartialOffset(path string, state downloadCheckpointState, key bool) int64 {
+	if state.Validator == "" || key {
+		return 0
+	}
+	info, err := os.Stat(path)
+	if err != nil || info.IsDir() || info.Size() <= 0 || state.Total > 0 && info.Size() > state.Total {
+		return 0
+	}
+	return info.Size()
+}
+
+func runDownloadCheckpoint(ctx context.Context, address, target, statePath string, key bool, build downloadCheckpointRequest, fetch downloadCheckpointFetch, progress func(int64, int64)) (int64, error) {
+	if !isProviderHTTPMediaURL(address) {
+		return 0, errors.New("媒体下载地址无效")
+	}
+	if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
+		return 0, err
+	}
+	partial := target + ".part"
+	state := readDownloadCheckpoint(statePath, address)
+	if size, ok := checkpointExistingComplete(target, state, key); ok {
+		if progress != nil {
+			progress(size, size)
+		}
+		return size, nil
+	}
+	_ = os.Remove(target)
+	offset := checkpointPartialOffset(partial, state, key)
+	for restart := 0; restart < 2; restart++ {
+		size, reset, err := runDownloadCheckpointAttempt(ctx, address, target, partial, statePath, key, offset, state, build, fetch, progress)
+		if !reset {
+			return size, err
+		}
+		offset, state = 0, downloadCheckpointState{}
+		_ = os.Remove(partial)
+		_ = os.Remove(statePath)
+	}
+	return 0, errors.New("服务器无法恢复下载，请重试")
+}
+
+func runDownloadCheckpointAttempt(ctx context.Context, address, target, partial, statePath string, key bool, offset int64, old downloadCheckpointState, build downloadCheckpointRequest, fetch downloadCheckpointFetch, progress func(int64, int64)) (int64, bool, error) {
+	request, err := build(ctx, offset, old.Validator)
+	if err != nil {
+		return 0, false, err
+	}
+	response, err := fetch(request)
+	if err != nil {
+		return offset, false, err
+	}
+	defer response.Body.Close()
+	if offset > 0 && (response.StatusCode == http.StatusRequestedRangeNotSatisfiable || response.StatusCode == http.StatusPreconditionFailed) {
+		return 0, true, nil
+	}
+	if response.StatusCode != http.StatusOK && response.StatusCode != http.StatusPartialContent {
+		return offset, false, fmt.Errorf("媒体下载失败 HTTP %d", response.StatusCode)
+	}
+	if response.StatusCode == http.StatusOK {
+		offset = 0
+	}
+	if !identityMediaResponse(response) {
+		return offset, false, errors.New("服务器返回了压缩或分段媒体响应，无法安全续传")
+	}
+	contentType := strings.ToLower(response.Header.Get("Content-Type"))
+	if !key && (strings.Contains(contentType, "text/html") || strings.Contains(contentType, "application/json")) {
+		return offset, false, errors.New("站源返回了错误页面，请刷新下载地址后重试")
+	}
+	total := response.ContentLength
+	validator := downloadHTTPValidator(response.Header)
+	if response.StatusCode == http.StatusPartialContent {
+		span, valid := parseMediaByteRange(response.Header.Get("Content-Range"))
+		if !valid || span.start != offset || response.ContentLength >= 0 && response.ContentLength != span.end-span.start+1 {
+			return offset, false, errors.New("服务器返回的续传范围不正确，已停止下载")
+		}
+		if offset > 0 && (validator != "" && validator != old.Validator || old.Total > 0 && old.Total != span.total) {
+			return 0, true, nil
+		}
+		total = span.total
+	}
+	if key && (total > 64 || offset > 0) {
+		return offset, false, errors.New("视频密钥格式无效")
+	}
+	state := downloadCheckpointState{URL: address, Validator: validator, Total: total}
+	if err := writeDownloadCheckpoint(statePath, state); err != nil {
+		return offset, false, err
+	}
+	flags := os.O_CREATE | os.O_WRONLY
+	if offset == 0 {
+		flags |= os.O_TRUNC
+	} else {
+		flags |= os.O_APPEND
+	}
+	file, err := os.OpenFile(partial, flags, 0o600)
+	if err != nil {
+		return offset, false, err
+	}
+	received := offset
+	buffer := make([]byte, 64<<10)
+	for {
+		count, readErr := response.Body.Read(buffer)
+		if count > 0 {
+			if key && received+int64(count) > 64 {
+				err = errors.New("视频密钥过大")
+				break
+			}
+			written, writeErr := file.Write(buffer[:count])
+			received += int64(written)
+			if writeErr != nil || written != count {
+				err = errors.New("写入下载文件失败，请检查剩余空间")
+				break
+			}
+			if progress != nil {
+				progress(received, total)
+			}
+		}
+		if readErr != nil {
+			if readErr != io.EOF {
+				err = errors.New("媒体文件未接收完整，点击继续下载")
+			}
+			break
+		}
+		if ctxErr := ctx.Err(); ctxErr != nil {
+			err = ctxErr
+			break
+		}
+	}
+	if err == nil && (received == 0 || total >= 0 && received != total) {
+		err = errors.New("媒体文件未接收完整，点击继续下载")
+	}
+	if err == nil && key && received != 16 {
+		err = errors.New("视频密钥长度无效")
+	}
+	if err == nil {
+		err = file.Sync()
+	}
+	closeErr := file.Close()
+	if err != nil {
+		return received, false, err
+	}
+	if closeErr != nil {
+		return received, false, closeErr
+	}
+	if err = os.Rename(partial, target); err != nil {
+		return received, false, err
+	}
+	state.Complete, state.Total = true, received
+	if err = writeDownloadCheckpoint(statePath, state); err != nil {
+		return received, false, err
+	}
+	return received, false, nil
+}
+
+func directDownloadMedia(media providerMedia, key []byte) bool {
+	if media.Playlist != "" || len(key) > 0 || len(media.HLSKey) > 0 || len(media.CENCKey) > 0 || !validProviderMediaCredentials(media.credentials, providerMediaCredentialReserve) {
+		return false
+	}
+	parsed, err := url.Parse(media.URL)
+	return err == nil && strings.HasSuffix(strings.ToLower(parsed.Path), ".mp4")
+}
+
+func (d *Downloader) downloadDirectProviderMedia(ctx context.Context, task Task, media providerMedia, key []byte, progress *downloadProgressState) (bool, error) {
+	if !directDownloadMedia(media, key) {
+		return false, nil
+	}
+	candidates := append([]providerMedia{media}, mediaFallbackVariants(media)...)
+	client := *d.client
+	client.Timeout = 0
+	var lastErr error
+	for _, candidate := range candidates {
+		if !directDownloadMedia(candidate, key) {
+			continue
+		}
+		build := func(ctx context.Context, offset int64, validator string) (*http.Request, error) {
+			request, err := http.NewRequestWithContext(providerMediaContext(ctx, candidate.credentials), http.MethodGet, candidate.URL, nil)
+			if err != nil {
+				return nil, err
+			}
+			request.Header.Set("Referer", candidate.Referer)
+			request.Header.Set("Accept-Encoding", "identity")
+			if offset > 0 {
+				request.Header.Set("Range", fmt.Sprintf("bytes=%d-", offset))
+				request.Header.Set("If-Range", validator)
+			}
+			return request, nil
+		}
+		fetch := func(request *http.Request) (*http.Response, error) {
+			return d.doMediaRequestWithClient(request, &client)
+		}
+		size, err := runDownloadCheckpoint(ctx, candidate.URL, task.OutPath, task.OutPath+".download.json", false, build, fetch, func(received, total int64) {
+			if progress == nil {
+				return
+			}
+			progress.setByteProgress(received, total)
+			progress.report("downloading", false)
+		})
+		if err == nil {
+			if progress != nil {
+				progress.setTotalBytes(size)
+				progress.report("completed", true)
+			}
+			return true, nil
+		}
+		lastErr = err
+	}
+	return true, lastErr
+}
+
+func prepareDownloadMediaCache(directory string, media providerMedia, key []byte) (*downloadMediaCache, error) {
+	fingerprint := sha256.New()
+	for _, value := range []string{media.URL, media.Referer, media.Playlist, hex.EncodeToString(media.HLSKey), hex.EncodeToString(media.CENCKey), hex.EncodeToString(key), fmt.Sprint(media.Quality)} {
+		_, _ = fingerprint.Write([]byte(value))
+		_, _ = fingerprint.Write([]byte{0})
+	}
+	marker := hex.EncodeToString(fingerprint.Sum(nil))
+	markerPath := filepath.Join(directory, ".fingerprint")
+	if previous, err := os.ReadFile(markerPath); err == nil && strings.TrimSpace(string(previous)) != marker {
+		if err := os.RemoveAll(directory); err != nil {
+			return nil, err
+		}
+	}
+	if err := os.MkdirAll(directory, 0o700); err != nil {
+		return nil, err
+	}
+	if err := writeNewViewerFile(markerPath, []byte(marker)); err != nil {
+		if !errors.Is(err, os.ErrExist) {
+			return nil, err
+		}
+		if previous, readErr := os.ReadFile(markerPath); readErr != nil || strings.TrimSpace(string(previous)) != marker {
+			return nil, errors.New("下载检查点无法保存")
+		}
+	}
+	return &downloadMediaCache{directory: directory}, nil
+}
+
+func (cache *downloadMediaCache) path(address string) (string, string) {
+	sum := sha256.Sum256([]byte(address))
+	base := filepath.Join(cache.directory, hex.EncodeToString(sum[:]))
+	return base + ".bin", base + ".json"
+}
+
+func (cache *downloadMediaCache) open(ctx context.Context, proxy *hlsProxy, asset hlsAsset, build func(hlsAsset) (*http.Request, error)) (*os.File, int64, error) {
+	target, statePath := cache.path(asset.remote)
+	buildRequest := func(ctx context.Context, offset int64, validator string) (*http.Request, error) {
+		request, err := build(asset)
+		if err != nil {
+			return nil, err
+		}
+		request = request.WithContext(ctx)
+		request.Header.Set("Accept-Encoding", "identity")
+		if offset > 0 {
+			request.Header.Set("Range", fmt.Sprintf("bytes=%d-", offset))
+			request.Header.Set("If-Range", validator)
+		}
+		return request, nil
+	}
+	size, err := runDownloadCheckpoint(ctx, asset.remote, target, statePath, asset.extension == ".key", buildRequest, proxy.fetch, nil)
+	if err != nil {
+		return nil, 0, err
+	}
+	file, err := os.Open(target)
+	return file, size, err
+}
diff --git a/internal/app/download_directories.go b/internal/app/download_directories.go
new file mode 100644
index 0000000..faeadcf
--- /dev/null
+++ b/internal/app/download_directories.go
@@ -0,0 +1,228 @@
+package app
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func dramaSourceFolder(drama Drama) string {
+	source := accountSourceGroup(firstNonEmpty(drama.Source, sourceFromDramaID(drama.ID)))
+	if source == "" {
+		source = accountDramaSource(drama.ID)
+	}
+	for _, choice := range accountSourceChoices {
+		if choice.ID == source {
+			return safeFilename(choice.Name)
+		}
+	}
+	return "其他来源"
+}
+
+func readDownloadDirectoryID(directory string) (string, error) {
+	path := filepath.Join(directory, ".drama-id")
+	info, err := os.Lstat(path)
+	if errors.Is(err, os.ErrNotExist) {
+		return "", nil
+	}
+	if err != nil {
+		return "", err
+	}
+	if !info.Mode().IsRegular() || info.Size() > 1024 {
+		return "", errors.New("下载目录标识不是有效的普通文件")
+	}
+	body, err := os.ReadFile(path)
+	return strings.TrimSpace(string(body)), err
+}
+
+func scanDownloadDirectories(root string) (map[string]string, error) {
+	directories := make(map[string]string)
+	groups := map[string]bool{}
+	for _, choice := range accountSourceChoices {
+		groups[safeFilename(choice.Name)] = true
+	}
+	var scan func(string, bool) error
+	scan = func(parent string, grouped bool) error {
+		entries, err := os.ReadDir(parent)
+		if errors.Is(err, os.ErrNotExist) {
+			return nil
+		}
+		if err != nil {
+			return err
+		}
+		for _, entry := range entries {
+			if !entry.IsDir() || entry.Type()&os.ModeSymlink != 0 {
+				continue
+			}
+			directory := filepath.Join(parent, entry.Name())
+			id, err := readDownloadDirectoryID(directory)
+			if err != nil {
+
+				continue
+			}
+			if id != "" {
+				if sourceFromDramaID(id) != sourceHongguo {
+					continue
+				}
+				if previous, exists := directories[id]; exists && previous != directory {
+					directories[id] = ""
+				} else if !exists {
+					directories[id] = directory
+				}
+			} else if !grouped && groups[entry.Name()] {
+				if err := scan(directory, true); err != nil {
+					return err
+				}
+			}
+		}
+		return nil
+	}
+	err := scan(root, false)
+	return directories, err
+}
+
+func claimDownloadDirectory(directory, id string, known bool) (bool, error) {
+	if err := os.MkdirAll(directory, 0755); err != nil {
+		return false, err
+	}
+	info, err := os.Lstat(directory)
+	if err != nil {
+		return false, err
+	}
+	if !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {
+		return false, errors.New("下载剧集目录不是普通文件夹")
+	}
+	owner, err := readDownloadDirectoryID(directory)
+	if err != nil || owner != "" {
+		return owner == id, err
+	}
+	if !known {
+		entries, err := os.ReadDir(directory)
+		if err != nil {
+			return false, err
+		}
+		if len(entries) > 0 {
+			return false, nil
+		}
+	}
+	file, err := os.OpenFile(filepath.Join(directory, ".drama-id"), os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
+	if errors.Is(err, os.ErrExist) {
+		owner, readErr := readDownloadDirectoryID(directory)
+		return owner == id, readErr
+	}
+	if err != nil {
+		return false, err
+	}
+	_, err = file.WriteString(id)
+	if closeErr := file.Close(); err == nil {
+		err = closeErr
+	}
+	return err == nil, err
+}
+
+func downloadSourceDirectory(root, source string) (string, error) {
+	if err := os.MkdirAll(root, 0755); err != nil {
+		return "", err
+	}
+	directory := filepath.Join(root, source)
+	if err := os.Mkdir(directory, 0755); err != nil && !errors.Is(err, os.ErrExist) {
+		return "", err
+	}
+	info, err := os.Lstat(directory)
+	if err != nil {
+		return "", err
+	}
+	if !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {
+		return "", errors.New("下载站源目录不是普通文件夹")
+	}
+	if _, err = os.Lstat(filepath.Join(directory, ".drama-id")); !errors.Is(err, os.ErrNotExist) {
+		if err != nil {
+			return "", err
+		}
+		return "", fmt.Errorf("站源目录“%s”与已有剧集目录同名，请更换新下载的根目录；原剧集仍使用原目录", source)
+	}
+	return directory, nil
+}
+
+func (d *Downloader) downloadDramaDirectory(drama Drama, title, existing string) (string, error) {
+	var valid bool
+	drama, valid = normalizeHongguoDrama(drama)
+	if !valid {
+		return "", errors.New("此版本仅支持红果剧集")
+	}
+	d.directoryMu.Lock()
+	defer d.directoryMu.Unlock()
+	if drama.ID == "" || len(drama.ID) > 512 || strings.ContainsAny(drama.ID, "\x00\r\n") {
+		return "", errors.New("下载剧集标识无效")
+	}
+	if d.downloadDirectories == nil {
+		var err error
+		d.downloadDirectories, err = scanDownloadDirectories(d.cfg.OutputDir)
+		if err != nil {
+			d.downloadDirectories = nil
+			return "", err
+		}
+	}
+	if existing == "" {
+		var found bool
+		existing, found = d.downloadDirectories[drama.ID]
+		if found && existing == "" {
+			return "", errors.New("发现本剧的多个已有目录，请保留下载任务以确定更新位置")
+		}
+	}
+	if existing != "" {
+		ok, err := claimDownloadDirectory(existing, drama.ID, true)
+		if err != nil {
+			return "", err
+		}
+		if !ok {
+			return "", errors.New("已有下载目录属于其他剧集，原文件已保留")
+		}
+		d.downloadDirectories[drama.ID] = existing
+		return existing, nil
+	}
+	root := d.cfg.OutputDir
+	grouped := d.cfg.GroupBySource
+	if d.downloadGrouping != nil {
+		grouped = *d.downloadGrouping
+	}
+	if grouped {
+		var err error
+		root, err = downloadSourceDirectory(root, dramaSourceFolder(drama))
+		if err != nil {
+			return "", err
+		}
+	}
+	for _, name := range []string{title, title + "_" + hashShort(drama.ID)} {
+		directory, err := safeJoin(root, name)
+		if err != nil {
+			return "", err
+		}
+		ok, err := claimDownloadDirectory(directory, drama.ID, false)
+		if err != nil {
+			return "", err
+		}
+		if ok {
+			d.downloadDirectories[drama.ID] = directory
+			return directory, nil
+		}
+	}
+	return "", errors.New("下载目录存在同名内容，原文件已保留")
+}
+
+func (app *UIApp) dramaDirectoryLocked(id string) string {
+	if directory := app.dramaDirectories[id]; directory != "" {
+		return directory
+	}
+	for _, taskID := range app.taskOrder {
+		if task := app.tasks[taskID]; task != nil && task.DramaID == id && !isChapterPlaceholderTask(task) && task.Path != "" {
+			return filepath.Dir(task.Path)
+		}
+	}
+	if merged := app.merges[id]; merged != nil && merged.OutputPath != "" {
+		return filepath.Dir(merged.OutputPath)
+	}
+	return ""
+}