f1032865f3
If `ip route show default` returns no output the old code passed
an empty string to curl --resolve, producing a confusing error 6
("couldn't resolve host") with no indication that gateway detection
had failed. The new guard exits immediately with a clear message.
Addresses review concern raised by Tobias Wendt.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>