Integrate private destinations for layered inputs

internal/engine/layered.go

@@ -2,11 +2,12 @@ package engine
 
 import "os"
 
-// Input selects one source and its independent import policy.
+// Input selects one source, its destination, and its independent import policy.
 type Input struct {
-	Source     Source
-	Imports    bool
-	Filesystem *FilesystemContext
+	Source      Source
+	Imports     bool
+	Filesystem  *FilesystemContext
+	Destination Path
 }
 
 // Underlay contains strictly composed contributions at one precedence tier.
@@ -32,7 +33,10 @@ func LoadLayered[T any](main Input, secrets SecretBinding, supplied ...LayeredOp
 		options = supplied[0]
 	}
 	request := loadRequest[T]{
-		main:       loadInput{source: main.Source, imports: main.Imports, filesystem: main.Filesystem},
+		main: loadInput{
+			source: main.Source, imports: main.Imports, filesystem: main.Filesystem,
+			destination: main.Destination.clone(),
+		},
 		definition: options.Definition, overlay: options.Overlay,
 		overlayFilesystem: options.OverlayFilesystem,
 		overrides:         append([]Override(nil), options.Overrides...),
@@ -43,6 +47,7 @@ func LoadLayered[T any](main Input, secrets SecretBinding, supplied ...LayeredOp
 		for inputIndex, input := range underlay.Inputs {
 			request.underlays[index].inputs[inputIndex] = loadInput{
 				source: input.Source, imports: input.Imports, filesystem: input.Filesystem,
+				destination: input.Destination.clone(),
 			}
 		}
 	}