History-sharing-on-invite: key bundles from unknown senders are ignored when "Exclude insecure devices" is set #5770
Description
Suppose Alice and Bob do not currently share a room.
- Alice invites Bob to an encrypted room, and shares history.
- Bob receives the to-device message, including the
sender_device_keys, but he does not yet have a copy of Alice's identity key. - He is therefore unable to verify the cross-signature on the device in
sender_device_keys, and ignores the to-device message