I use Orbot on rooted android phone, I set it to „Tor everything“.
I want all apps to go through tor network or not connect at all. Now, I use wifi connection that sometimes disconnects, how can I be sure that Firefox app and other apps don't go to clearnet in that short period of time when Orbot is making a connection to Tor network?
is there a way to forbid all apps to connect if Orbot is not connected?
If Orbot is already connected, and your Wi-Fi is disconnected for a short period, Orbot will either wait for a connection, or attempt to establish circuits via your mobile connection if your device has one. Apps will not be able to use the clearnet if this happens.
However, some apps may be able to use the clearnet while your device is booting, before Orbot gets a chance to set iptables. I'm guessing you could fix that by manually editing iptables, but I'm not sure.
Just one 100% fail-safe way: use routing middlebox, that will be a hotspot which routes all the traffic through Tor. Other ways suffer from "jailbreaks", especially on boot-up - check with Wireshark/tcpdump
