OptionalmaxStop after dispatching this many effect entries, leaving the rest pending
for a later call. A whole number, one or more; anything else throws. One
entry counts once however many times its retry policy re-invokes the
handler. An entry skipped for a missing handler, or one another drainer
claimed first, does not count at all. Omitted dispatches every claimable
entry.
OptionalnamesRestrict to specific effect names. At least one name; an empty list
throws. Omitted considers every claimable entry, including ones no
handler covers, which missingHandler then decides.
Args for Engine.drainEffects — the drainer's identity is the engine client's token, like every other verb.