Create the event loop after daemonizing, not before

[stupalov]

Problem

--daemonize is broken: the responder binds its socket, logs Listening at UDP/IPv4 endpoint …, and then vanishes a fraction of a second later, leaving no PID file, no traceback and no log entry beyond a normal Process terminated.

The cause is the order of two things in main(). The Python 3.14 compatibility fix (1.2.1) creates the default event loop at the very top of main(); daemon.daemonize() then forks twice. An asyncio event loop does not survive fork() — its selector (kqueue/epoll) and self-pipe descriptors belong to the parent — so the daemon ends up running a loop whose descriptors are invalid:

File "pysnmp/carrier/asyncio/dispatch.py", line 78, in run_dispatcher
  self.loop.run_forever()
…
OSError: [Errno 9] Bad file descriptor

daemonize() has already pointed stderr at /dev/null by then, so the traceback is lost and the process simply disappears — which is what makes this hard to diagnose in the field. Before 1.2.1 the loop was created lazily by AsyncioDispatcher, i.e. after the fork, so daemon mode worked.

Fix

Move the loop creation below the --daemonize block, so the daemon creates its own loop after the fork. Nothing between the two points touches asyncio. Non-daemon startup is unaffected: the loop is still created before the dispatcher is built.

The same reordering is applied to responder_lite.py, which has the identical pattern.

Verification

Before: --daemonize exits within a second, no PID file. After: the daemon stays up, writes its PID file, answers SNMP, and SIGTERM shuts it down cleanly and removes the PID file.

$ snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1:1651 \
    --data-dir=tests/data/short-oid --daemonize --pid-file=/tmp/d.pid
$ snmpget -v2c -c public udp:127.0.0.1:1651 .1.3.6.1.2.1.47.1.1.1.1.3.2
SNMPv2-SMI::mib-2.47.1.1.1.1.3.2 = OID: SNMPv2-SMI::zeroDotZero

Found while setting up a daemonized start script for a public simulator, where the responder kept dying seconds after startup. It is now running daemonized in production.