Routes a value being stored to the one branch admitting it against every constraint, so that a caller ingesting a
value against a polymorphic shape settles it on a definite branch. A value admitted by several branches is ambiguous
and one admitted by none unsatisfiable; both yield nothing rather than a branch chosen by guesswork.
Picks the single branch a data value belongs to.
Routes a value being stored to the one branch admitting it against every constraint, so that a caller ingesting a value against a polymorphic shape settles it on a definite branch. A value admitted by several branches is ambiguous and one admitted by none unsatisfiable; both yield nothing rather than a branch chosen by guesswork.