May be missing something here. Experimenting with BMessage return addresses, as in BMessage::ReturnAddress, BMessage::SendReply etc. …
… and there doesn’t seem to be any such thing, in messages sent via BLooper::PostMessage().
A BMessage from an attached BControl has a messenger in it, but that’s just ironic because there doesn’t seem to be any use for it there. The use case, for me anyway, is messages posted back and forth between threads. For those messages, BMessage::ReturnAddress() yields a BMessenger to the BApplication, not the originating BWindow thread.
Is there a better way to post messages between threads, such that BMessage::SendReply() will work from the posted message?