Integrate source version checks for main inputs

internal/engine/layered.go

@@ -16,6 +16,7 @@ type Underlay struct{ Inputs []Input }
 // LayeredOptions selects lower-priority tiers and final application rules.
 type LayeredOptions[T any] struct {
 	Definition        Definition[T]
+	SourceVersionMode sourceVersionMode
 	Underlays         []Underlay
 	Overlay           string
 	OverlayFilesystem *FilesystemContext
@@ -37,7 +38,8 @@ func LoadLayered[T any](main Input, secrets SecretBinding, supplied ...LayeredOp
 			source: main.Source, imports: main.Imports, filesystem: main.Filesystem,
 			destination: main.Destination.clone(),
 		},
-		definition: options.Definition, overlay: options.Overlay,
+		definition: options.Definition, sourceVersionMode: options.SourceVersionMode,
+		overlay:           options.Overlay,
 		overlayFilesystem: options.OverlayFilesystem,
 		overrides:         append([]Override(nil), options.Overrides...),
 		underlays:         make([]loadGroup, len(options.Underlays)),