commit 9c7070106010c7335b2090fda67bd133a04351e9
Adds input cast validation to `transformer`
Whenever a cast is consumed from `transformer`, a cast validation is now
performed.
This commit makes even more natural to develop the commands as the developer
doesn't need to worry about receiving invalid casts.
Naturally, that's the expectation - there might exist a case when a
a command could potentially *want* to receive an invalid cast (which is
not the situation right now).
Example
(before it wouldn't produce an early fail)
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