fx's event lines, errors included, now log at debug level, so a normal
start shows none and DEBUG shows them. RunServer starts and stops the
fx app itself instead of calling Run, and logs fx's "received signal"
line as Run did. When the start fails, it logs the error's root cause
as one "cannot start" line, the backend's last, and returns 1. Main
returns the server's exit code.
Model: opus-5-5
sneak