fix: resolve 8 architecture flaws across download, playlist, and webhook

- Add --continue and --max-filesize to yt-dlp for download resilience
- Route thumbnail downloads through HTTP_PROXY
- Show per-video progress (i/N) with cancel for playlist downloads
- Run playlist asynchronously so cancel callbacks can be processed
- Guard handlePlaylistConfirm against concurrent active jobs
- Close Done channel in playlist entry lifecycle
- Add stepState TTL (30 min) to prevent stale states
- Wrap webhook server for graceful shutdown on SIGTERM
- Refactor formatBytes to loop-based implementation
- Show first line of stderr in user-facing error messages
- Fix format pointer reuse in playlist loop
- Add CreatedAt field to stepState for TTL tracking
- Add MaxFileSize and ProgressPrefix fields to DownloadJob

internal/handler/download.go

@@ -31,12 +31,20 @@ type stepState struct {
 	FormatIDs     []string
 	PlaylistState *domain.PlaylistState
 	SearchState   *domain.SearchState
+	CreatedAt     time.Time
 }
 
+const stepStateTTL = 30 * time.Minute
+
 func (h *Handler) getUserStepState(chatID int64) *stepState {
 	h.stepStatesMu.Lock()
 	defer h.stepStatesMu.Unlock()
-	return h.stepStates[chatID]
+	ss := h.stepStates[chatID]
+	if ss != nil && time.Since(ss.CreatedAt) > stepStateTTL {
+		delete(h.stepStates, chatID)
+		return nil
+	}
+	return ss
 }
 
 func (h *Handler) setUserStepState(chatID int64, ss *stepState) {
@@ -133,6 +141,7 @@ func (h *Handler) handleURLInput(ctx context.Context, chatID int64, text string,
 		URL:       url,
 		MediaInfo: info,
 		Step:      0,
+		CreatedAt: time.Now(),
 	}
 
 	h.sendMediaPreview(ctx, chatID, info)
@@ -348,6 +357,7 @@ func (h *Handler) startDownload(ctx context.Context, chatID int64, msgID int, us
 		Status:         domain.StatusDownloading,
 		Title:          ss.MediaInfo.Title,
 		FileSize:       fileSize,
+		MaxFileSize:    h.maxFileSize,
 		Done:           make(chan struct{}),
 	}
 
@@ -375,9 +385,13 @@ func (h *Handler) runDownload(ctx context.Context, job *domain.DownloadJob) {
 	defer func() { <-h.downloadSem }()
 
 	kb := progressKeyboard(0, "", "")
+	progressHeader := "Downloading: " + job.Title
+	if job.ProgressPrefix != "" {
+		progressHeader = job.ProgressPrefix + "\n" + progressHeader
+	}
 	msg, err := h.Bot.SendMessage(ctx, &tgbot.SendMessageParams{
 		ChatID:      job.ChatID,
-		Text:        fmt.Sprintf("Downloading: %s", job.Title),
+		Text:        progressHeader,
 		ReplyMarkup: &kb,
 	})
 	if err != nil {
@@ -390,7 +404,9 @@ func (h *Handler) runDownload(ctx context.Context, job *domain.DownloadJob) {
 	if err != nil {
 		errMsg := err.Error()
 		if job.StderrLog != "" {
-			errMsg += ": " + job.StderrLog
+			if lines := strings.SplitN(job.StderrLog, "\n", 2); len(lines) > 0 && lines[0] != "" {
+				errMsg = strings.TrimSpace(lines[0])
+			}
 		}
 		h.editText(ctx, job.ChatID, job.MessageID, fmt.Sprintf("Download failed: %s", errMsg), nil)
 		job.Status = domain.StatusFailed
@@ -460,7 +476,10 @@ func (h *Handler) trackDownloadProgress(ctx context.Context, job *domain.Downloa
 			}
 
 			kb := progressKeyboard(upd.Progress, upd.Speed, upd.ETA)
-			text := fmt.Sprintf("Downloading: %s", job.Title)
+			text := "Downloading: " + job.Title
+			if job.ProgressPrefix != "" {
+				text = job.ProgressPrefix + "\n" + text
+			}
 			h.editText(ctx, job.ChatID, job.MessageID, text, &kb)
 
 		case <-ctx.Done():
@@ -732,7 +751,13 @@ func (h *Handler) sendMediaPreview(ctx context.Context, chatID int64, info *doma
 
 // downloadFile downloads a URL to a temp file in the given directory and returns the path.
 func downloadFile(url, dir string) (string, error) {
-	client := &http.Client{Timeout: 30 * time.Second}
+	tr := &http.Transport{
+		Proxy: http.ProxyFromEnvironment,
+	}
+	client := &http.Client{
+		Timeout:   30 * time.Second,
+		Transport: tr,
+	}
 	resp, err := client.Get(url)
 	if err != nil {
 		return "", fmt.Errorf("http get: %w", err)