A lone array callback in a local class's method could read a binding the
method reaches through its class's captures. Those bindings are shared by
every method of the class, so another method can assign one while the
loop runs, but the copied loop read the value once when the call started.
stableTarget now counts a method's class captures as inherited, so such
a callback keeps its helper and reads the current value on every call.
Chris Tate
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