internal/rosa: extra inputs in alternative path

This works around particularly unwieldy build systems.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/azalea/evaluate.go

@@ -142,6 +142,8 @@ var (
 	IdentInputs = unique.Make(Ident("inputs"))
 	// IdentRuntime has the same semantics as [IdentInputs].
 	IdentRuntime = unique.Make(Ident("runtime"))
+	// IdentExtra has the same semantics as [IdentInputs].
+	IdentExtra = unique.Make(Ident("extra"))
 	// IdentSource is a special argument in a package declaration where an
 	// assignment of a [Val] with a single [Ident] passes through the evaluator.
 	IdentSource = unique.Make(Ident("source"))
@@ -291,6 +293,7 @@ func evaluateAny(d PF, s []Frame, expr, rp any) bool {
 				for _, special := range [...]unique.Handle[Ident]{
 					IdentInputs,
 					IdentRuntime,
+					IdentExtra,
 				} {
 					if slices.Contains(names, special) {
 						if len(names) != 1 || len(arg.V) != 1 || arg.R {