fix(telegram): delete placeholder message when streaming delivers response

When streaming was active, the "Thinking..." placeholder message stayed
in the chat because preSend only deleted the tracking entry without
removing the actual Telegram message. Now preSend deletes the placeholder
via the new MessageDeleter interface when streamActive is set.

pkg/channels/interfaces.go

@@ -15,6 +15,11 @@ type MessageEditor interface {
 	EditMessage(ctx context.Context, chatID string, messageID string, content string) error
 }
 
+// MessageDeleter — channels that can delete a message by ID.
+type MessageDeleter interface {
+	DeleteMessage(ctx context.Context, chatID string, messageID string) error
+}
+
 // ReactionCapable — channels that can add a reaction (e.g. 👀) to an inbound message.
 // ReactToMessage adds a reaction and returns an undo function to remove it.
 // The undo function MUST be idempotent and safe to call multiple times.

pkg/channels/manager.go

@@ -133,10 +133,18 @@ func (m *Manager) preSend(ctx context.Context, name string, msg bus.OutboundMess
 		}
 	}
 
-	// 3. If a stream already finalized this message, skip both placeholder and send
+	// 3. If a stream already finalized this message, delete the placeholder and skip send
 	if _, loaded := m.streamActive.LoadAndDelete(key); loaded {
-		// Also clean up any stale placeholder
-		m.placeholders.Delete(key)
+		if v, loaded := m.placeholders.LoadAndDelete(key); loaded {
+			if entry, ok := v.(placeholderEntry); ok && entry.id != "" {
+				// Prefer deleting the placeholder (cleaner UX than editing to same content)
+				if deleter, ok := ch.(MessageDeleter); ok {
+					deleter.DeleteMessage(ctx, msg.ChatID, entry.id) // best effort
+				} else if editor, ok := ch.(MessageEditor); ok {
+					editor.EditMessage(ctx, msg.ChatID, entry.id, msg.Content) // fallback
+				}
+			}
+		}
 		return true
 	}
 

pkg/channels/telegram/telegram.go

@@ -301,6 +301,22 @@ func (c *TelegramChannel) EditMessage(ctx context.Context, chatID string, messag
 	return err
 }
 
+// DeleteMessage implements channels.MessageDeleter.
+func (c *TelegramChannel) DeleteMessage(ctx context.Context, chatID string, messageID string) error {
+	cid, err := parseChatID(chatID)
+	if err != nil {
+		return err
+	}
+	mid, err := strconv.Atoi(messageID)
+	if err != nil {
+		return err
+	}
+	return c.bot.DeleteMessage(ctx, &telego.DeleteMessageParams{
+		ChatID:    tu.ID(cid),
+		MessageID: mid,
+	})
+}
+
 // SendPlaceholder implements channels.PlaceholderCapable.
 // It sends a placeholder message (e.g. "Thinking... 💭") that will later be
 // edited to the actual response via EditMessage (channels.MessageEditor).