What's the purpose of this initial encrypted message? The create_outbound function handles creating an initial encrypted message as part of X3DH initialization. Is a second "initial message" necessary? What does it achieve?

Never mind – I looked into some more, and this initial message is necessary. The create_inbound method on the other client needs the result of this

I'm confused why this change was included in this diff... it doesn't seem to be relevant to the rest of the diff

After getting through the whole diff stack, I still can't find where this is used.

Do we ever need overwrite = false? If yes, can you point out where it will be used? If not, then I think we don't think as a parameter, and can just change the behavior without introducing a new parameter.

Separately – can you provide some explanation for the change to default to overwriting?

This change is essential for this differential to work properly. Flat file where olm account for notifications is stored is cleaned only during the log out process. If the user tries to log in, gets one time key and prekey from the keyserver and establishes olm session on its side, but something goes wrong on the keyserver, then we will not be able to retry log in process if we don't change the behaviour of initializeOutboundForSendingSession (its behaviour is to throw an error on attempt to initialize session with the same user again). On the other hand, CryptoModule is a general purpose class that shouldn't be restricted to the case of NotificationsCryptoModule, so we have to keep it useful for someone else that might need the old behaviour.

Does it makes sense to print a log message here when this happens? That way the developer can be more aware if something unexpected occurs