expect + diff
Closes the "silent damage" gap: the agent confirms the action HAD
an effect, not just that the command was emitted.
NAC.expect(plugin, statePath, value, opts?) polls
until a state matches. NAC.diff(plugin, statePath, actionFn)
snapshots before / after an action and reports
{before, after, changed}. Both compose with
NAC.read() so any V25-01 backend works.