tcp_check swallowed every exception and icmp_check returned on a
non-zero exit without a reason, so every down ICMP/TCP monitor stored
error_msg NULL and the Monitors page and MCP showed it down with no why.
Each failure now names its cause: "No reply within 2 s", "Connection
refused on port N", "No answer on port N within 5 s", "Can't resolve
<name>: ...", the OS error, or ping's own first stderr line. An ICMP
check that fell back to TCP says so, and a ping that outlives its
timeout is killed rather than left running.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
bvandeusenandClaude Opus 5.5
ca12652277