Proposed resolution:

This wording is relative to N5046.

1. Modify [numeric.sat.cast] as indicated:

   template<class R, class T>
     constexpr R saturating_cast(T x) noexcept;
   

   -1- Constraints: `R` and `T` are signed or unsigned integer types ([basic.fundamental]).

   -2- Returns: If `x` is representable as a value of type `R`, `x`; otherwise, either the largest or smallest representable value of type `R`, whichever is closer to the value of `x`.

   -?- Remarks: An invocation may explicitly specify an argument for the template parameter `R`.

Currently, [algorithms.requirements]/15 allows implementations to reject explicitly specifying template arguments for algorithms. Unfortunately, `std::saturating_cast` is also an algorithm as it is specifying in the "Algorithms library" chapter, and its first template argument must be explicitly specified. Without being "explicitly stated otherwise", `std::saturating_cast` is effectively unusable.