fix(updates): drop the bot's own outgoing messages

MTProto echoes the bot's own sends back on the update stream with
Out=true (the HTTP Bot API never does). Without filtering them, a bot
that replies to messages answers its own replies in an infinite loop.
Skip Out messages in dispatchMessage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ernado

on.go

@@ -41,6 +41,13 @@ func (b *Bot) installHandlers() {
 // field. Channel-broadcast messages become channel posts; everything else is a
 // regular message. edited selects the edited_* fields.
 func (b *Bot) dispatchMessage(ctx context.Context, msg tg.MessageClass, edited bool) {
+	// Drop the bot's own outgoing messages. MTProto echoes them back on the
+	// update stream, but the HTTP Bot API never delivers them — without this a
+	// bot that replies to messages would answer its own replies in a loop.
+	if tgm, ok := msg.(*tg.Message); ok && tgm.Out {
+		return
+	}
+
 	m, err := b.messageFromTg(ctx, msg)
 	if err != nil {
 		b.log.Error("Convert message", zap.Error(err))

on_self_test.go

@@ -0,0 +1,29 @@
+package botapi
+
+import (
+	"context"
+	"testing"
+
+	"github.com/gotd/td/tg"
+)
+
+// TestDispatchSkipsOwnOutgoingMessage guards against the self-reply loop: the
+// bot's own messages arrive on the MTProto update stream with Out=true and must
+// not be dispatched to handlers.
+func TestDispatchSkipsOwnOutgoingMessage(t *testing.T) {
+	b := newTestBot(t)
+	fired := false
+	b.OnMessage(func(*Context) error { fired = true; return nil })
+
+	own := &tg.Message{
+		Out:     true,
+		ID:      1,
+		Message: "echo",
+		PeerID:  &tg.PeerUser{UserID: 42},
+	}
+	b.dispatchMessage(context.Background(), own, false)
+
+	if fired {
+		t.Fatal("handler fired for the bot's own outgoing message")
+	}
+}