chore: log business message peer diagnostic

Temporary: log how a business message's send peer resolves (present in the
update entities? access hash / min flag?) to pin down why a reply gets
BUSINESS_PEER_INVALID.

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

Author: ernado

business_updates.go

@@ -62,6 +62,7 @@ func (b *Bot) dispatchBusinessMessage(ctx context.Context, e tg.Entities, connec
 	m.BusinessConnectionID = connectionID
 	if m.raw != nil {
 		m.businessPeer = inputPeerFromEntities(m.raw.PeerID, e)
+		b.logBusinessPeerDiag(ctx, m.raw.PeerID, e, m.businessPeer)
 	}
 
 	u := &Update{}
@@ -74,6 +75,46 @@ func (b *Bot) dispatchBusinessMessage(ctx context.Context, e tg.Entities, connec
 	b.route(ctx, u)
 }
 
+// logBusinessPeerDiag logs how a business message's send peer was (or was not)
+// resolved, to diagnose BUSINESS_PEER_INVALID: whether the peer was present in
+// the update's entities, and the access hash / min flag carried there.
+func (b *Bot) logBusinessPeerDiag(ctx context.Context, peer tg.PeerClass, e tg.Entities, resolved tg.InputPeerClass) {
+	fields := []log.Attr{
+		log.String("raw_peer", peerKindString(peer)),
+		log.Bool("resolved_from_entities", resolved != nil),
+		log.Int("entity_users", len(e.Users)),
+		log.Int("entity_chats", len(e.Chats)),
+		log.Int("entity_channels", len(e.Channels)),
+	}
+
+	if pu, ok := peer.(*tg.PeerUser); ok {
+		if u, ok := e.Users[pu.UserID]; ok {
+			fields = append(fields,
+				log.Int64("entity_access_hash", u.AccessHash),
+				log.Bool("entity_min", u.Min),
+			)
+		} else {
+			fields = append(fields, log.Bool("user_in_entities", false))
+		}
+	}
+
+	b.logger().Info(ctx, "Business peer diagnostic", fields...)
+}
+
+// peerKindString describes a peer for diagnostics.
+func peerKindString(peer tg.PeerClass) string {
+	switch peer.(type) {
+	case *tg.PeerUser:
+		return peerKindUser
+	case *tg.PeerChat:
+		return peerKindChat
+	case *tg.PeerChannel:
+		return peerKindChannel
+	default:
+		return "none"
+	}
+}
+
 // inputPeerFromEntities builds the input peer for a message's chat from the
 // access hashes delivered with the update, so a business send addresses the chat
 // with the account's own access hash. Returns nil when the peer is absent.