on "event" {} handler

wcl block

Binds a wscript file to a lifecycle event; handler failures are logged, never fatal.

An on "<event>" {} block reacts to a lifecycle event by running a wscript file (fn handle(event, lab)).

on "vm.crashed"    { run = "scripts/collect-dumps.ws" }
on "vm.crashed"    { run = "scripts/page-oncall.ws"  targets = ["dc01", "srv01"] }
on "host.disk_low" { run = "scripts/alert.ws" }

targets narrows a handler to named machines; leave it out and the handler runs for every occurrence of the event. It is only legal on machine-scoped events — vm.*, container.* and snapshot.*. Declaring it on a lab-wide event (lab.up, host.disk_low, template.built, …) is a validation error: *event "x" is lab-wide and cannot declare targets*.

Handler failures are logged, never fatal. See the event list for every event name and the Event type for the handler payload.