https://code.briarproject.org/briar/briar-mailbox/-/issues/95
After the mailbox installation and at various points during the walk through the onboarding screens or during the do-not-kill-me fragment being displayed, or during the generation or display of QR code - change the internet settings on the device, or on router.
When mailbox device is not connected to the internet, the user should get the 'offline' screen... See here
At the time when this screen is displayed the notification should be appropriate too https://code.briarproject.org/briar/briar-mailbox/-/issues/140
Repeat using different devices, in landscape and portrait
After that screen is displayed, reconnect to the internet - the setup process should continue where it left off, or it should restart - but either way the interruption should behandled gracefully.