feat(updates): resolve forward origin on incoming messages

convertMessage now fills Message.ForwardOrigin from the MTProto forward header:
hidden senders become MessageOriginHiddenUser (no resolution); known users
resolve to MessageOriginUser; channel posts and other chats resolve to
MessageOriginChannel / MessageOriginChat with the author signature.

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

Author: ernado

convert.go

@@ -118,6 +118,49 @@ func (b *Bot) fillFrom(ctx context.Context, from tg.PeerClass, m *Message) error
 	return nil
 }
 
+// forwardOrigin maps an MTProto forward header into a Bot API MessageOrigin.
+// A hidden sender yields a hidden-user origin (no resolution); otherwise the
+// user or chat/channel is resolved via the peer manager.
+func (b *Bot) forwardOrigin(ctx context.Context, h *tg.MessageFwdHeader) (MessageOrigin, error) {
+	if name, ok := h.GetFromName(); ok {
+		return &MessageOriginHiddenUser{Type: OriginHiddenUser, Date: h.Date, SenderUserName: name}, nil
+	}
+
+	fromID, ok := h.GetFromID()
+	if !ok {
+		return nil, nil
+	}
+
+	if pu, ok := fromID.(*tg.PeerUser); ok {
+		u, err := b.peers.GetUser(ctx, &tg.InputUser{UserID: pu.UserID})
+		if err != nil {
+			return nil, asAPIError(err)
+		}
+		return &MessageOriginUser{Type: OriginUser, Date: h.Date, SenderUser: userFromTgUser(u.Raw())}, nil
+	}
+
+	chat, err := b.chatByPeer(ctx, fromID)
+	if err != nil {
+		return nil, err
+	}
+	author, _ := h.GetPostAuthor()
+	if post, ok := h.GetChannelPost(); ok && chat.Type == ChatTypeChannel {
+		return &MessageOriginChannel{
+			Type:            OriginChannel,
+			Date:            h.Date,
+			Chat:            chat,
+			MessageID:       post,
+			AuthorSignature: author,
+		}, nil
+	}
+	return &MessageOriginChat{
+		Type:            OriginChat,
+		Date:            h.Date,
+		SenderChat:      chat,
+		AuthorSignature: author,
+	}, nil
+}
+
 // convertMessage translates a tg.Message into a Bot API Message, resolving the
 // chat and sender via the peer manager. It fills the core fields (text,
 // entities, reply target, inline markup); richer media mapping arrives with the
@@ -156,6 +199,14 @@ func (b *Bot) convertMessage(ctx context.Context, m *tg.Message) (*Message, erro
 		r.ReplyToMessage = &Message{MessageID: rh.ReplyToMsgID}
 	}
 
+	if h, ok := m.GetFwdFrom(); ok {
+		origin, err := b.forwardOrigin(ctx, &h)
+		if err != nil {
+			return nil, err
+		}
+		r.ForwardOrigin = origin
+	}
+
 	if m.Message != "" {
 		r.Text = m.Message
 	}

convert_fwd_test.go

@@ -0,0 +1,31 @@
+package botapi
+
+import (
+	"context"
+	"testing"
+
+	"github.com/gotd/td/tg"
+)
+
+func TestForwardOriginHiddenUser(t *testing.T) {
+	b := newTestBot(t)
+	h := &tg.MessageFwdHeader{Date: 123}
+	h.SetFromName("Anon")
+
+	origin, err := b.forwardOrigin(context.Background(), h)
+	if err != nil {
+		t.Fatal(err)
+	}
+	hidden, ok := origin.(*MessageOriginHiddenUser)
+	if !ok || hidden.SenderUserName != "Anon" || hidden.Date != 123 {
+		t.Fatalf("expected hidden-user origin, got %#v", origin)
+	}
+}
+
+func TestForwardOriginNoSender(t *testing.T) {
+	b := newTestBot(t)
+	origin, err := b.forwardOrigin(context.Background(), &tg.MessageFwdHeader{Date: 1})
+	if err != nil || origin != nil {
+		t.Fatalf("no sender should yield (nil, nil), got (%#v, %v)", origin, err)
+	}
+}