Action
class ActionApplicationException(message: String, cause: Throwable? = null) : RuntimeException(source)
A write that failed partway through applying a plan.
This is the one place the subsystem cannot promise all-or-nothing: by the time it is thrown some levers have moved and some have not, and the message says how many. Where that matters, a model author declares the group as an atomic batch instead (§4.4.5).