When more than one invitation socket is opened, Alice should pick which one to use and Bob should use whichever one Alice picks. This fixes a race condition where each party picked a different socket and closed the other.

Each task is added to the back of the executor's queue, allowing tasks from other callers to be interleaved.

This avoids a potential problem where the app crashes after adding the contact but before adding the transport keys, leaving the contact unusable.

Poll for outgoing connections each time the network is enabled, then disable polling once our hidden service descriptor has been published.

Same exponential backoff approach as Bluetooth.

The polling interval increases exponentially each time polling is unsuccessful, up to a maximum of 60 minutes. The interval is reset to 2 minutes whenever a connection is made and whenever Bluetooth is re-enabled.