fix: resolve back step, audio labels, progress parsing, file size pre-check, and stale job cleanup

- Fix handleBackStep to redirect to download prompt when step state is nil
  (previously silent no-op after container selection cleared the state)
- Improve formatLabel for audio-only entries without bitrate: use ID + extension
  instead of generic 'audio', fixing duplicate entries in format list
- Add yt-dlp --progress-template for reliable JSON progress parsing across all
  sites (fixes 0.0% progress on sites like xnxx.com where [download] lines
  are absent); keep regex parser as fallback for older yt-dlp versions
- Add file size pre-check in handleContainerSelection before download starts
  (previously checked only after download completed, wasting bandwidth)
- Clear stale active jobs and step state on /start for a clean slate

internal/handler/download.go

@@ -346,6 +346,14 @@ func (h *Handler) handleContainerSelection(ctx context.Context, chatID int64, ms
 		format = ss.MainFormat
 	}
 
+	fileSize := format.Filesize
+
+	if fileSize > 0 && fileSize > h.maxFileSize {
+		h.editText(ctx, chatID, msgID,
+			fmt.Sprintf("File too large (%s). Max: %s", formatBytes(fileSize), formatBytes(h.maxFileSize)), nil)
+		return
+	}
+
 	job := &domain.DownloadJob{
 		ID:             h.generateJobID(),
 		UserID:         userID,
@@ -359,9 +367,10 @@ func (h *Handler) handleContainerSelection(ctx context.Context, chatID int64, ms
 		Language:       ss.Language,
 		Status:         domain.StatusDownloading,
 		Title:          ss.MediaInfo.Title,
-		FileSize:       format.Filesize,
+		FileSize:       fileSize,
 	}
 
+	h.editText(ctx, chatID, msgID, "Processing...", nil)
 	h.setActiveJob(userID, job)
 	h.clearStepState(chatID)
 
@@ -526,6 +535,7 @@ func (h *Handler) handleBackStep(ctx context.Context, chatID int64, msgID int, c
 	defer h.answerCb(ctx, cbID)
 	ss := h.getUserStepState(chatID)
 	if ss == nil {
+		h.handleDownloadPrompt(ctx, chatID, msgID, cbID, userID)
 		return
 	}
 

internal/handler/handler.go

@@ -442,9 +442,11 @@ func (h *Handler) generateJobID() string {
 	return uuid.NewString()[:8]
 }
 
-// handleStart shows the main menu.
+// handleStart shows the main menu and cleans up any stale state.
 func (h *Handler) handleStart(ctx context.Context, msg *models.Message, userID int64) {
 	slog.Info("start", "user_id", userID, "chat_id", msg.Chat.ID)
+	h.clearActiveJob(userID)
+	h.clearStepState(msg.Chat.ID)
 	h.sendWithKB(ctx, msg.Chat.ID, "Main Menu:", mainKeyboard())
 }