Each SNMP GET/WALK now runs in a forked child process. If libnetsnmp
triggers a SIGSEGV or other fatal signal, only the child dies - the
parent agent logs the crash and continues operating for all other devices.
Key changes:
- C helper: snmp_get_isolated() and snmp_walk_isolated() using
fork+pipe pattern with 60s alarm watchdog and mutex-serialized forks
- Rust: IsolationMode enum (Fork/Direct) controlled by
TOWEROPS_SNMP_ISOLATION env var, defaults to Fork
- New CrashRecovered error variant with signal info and logging
- Device poller logs crash recovery events at error level
- Startup logs active isolation mode
Set TOWEROPS_SNMP_ISOLATION=direct to disable isolation for debugging.
