Woke up to the upstairs machines and wifi down. Couldn't reach the router so I rebooted it. The router was never the problem.

The logs proved that much: everything wired stayed up all night, DHCP still serving leases at 6am, my desktop six days uptime.

Best guess is the wifi mesh, but I can't prove it. That's the point: it's the one layer with no logs to query. So the fix isn't a better guess, it's adding the logging it never had.

You can't diagnose what you don't monitor.