“Rule 615 ‘is not permissive’ but ‘mandates that witnesses be excluded’ absent a valid exception.” State v. Wilson, 2022 MT 11, ¶ 32, __ Mont. __, __ P.3d __ (quoting State v. Osborne, 1999 MT 149, ¶ 28, 295 Mont. 54, 982 P.2d 1045). “[W]hen a party requests an exclusion, and no exception applies, the decision is not committed to the trial court’s discretion.” Wilson, ¶ 32 (citation omitted). “But the decision whether a Rule 615 exception applies is reviewed for abuse of discretion.” Wilson, ¶ 32 (emphasis in original).