Nothing here reaches the heap, because while a task runs the heap is its
caller rather than something it can borrow. Sends and spawns accumulate as
requests the heap drains when the turn ends.
Where a task is: in this heap, or on the far side of one of this node’s
links. A host peer is not here - ('host name) is an ordinary cons, a name
the program writes, while a task address is a capability the runtime mints.
('task-down addr . result), where result is (ok . v), (throw . v),
(throw . noproc) for a task already gone when the monitor was set, or
(throw . noconnection) for one behind a link that died.