Consolidate selected overlay acquisition

internal/engine/source_version_test.go

@@ -1487,9 +1487,22 @@ func TestSourceVersionOverlayProtectsMountedMainAndPreservesSequenceCoordinates(
 			t.Fatalf("compose base: %#v", compositionDiagnostics)
 		}
 		assembly := newAssemblyAccumulator(base)
-		_, diagnostics = loadSelectedOverlayIntoWithVersion(
-			File(mainPath), nil, main, assembly, sourceInfos(main.source), "testing", effectiveRule, defaultImportLimits(), state,
-		)
+		resolved, diagnostic := resolveFilesystemContext(File(mainPath), nil, main, nil)
+		if diagnostic != nil {
+			t.Fatalf("resolve overlay context: %#v", diagnostic)
+		}
+		request := selectedOverlayRequest{
+			name: "testing", filesystem: resolved, protectionRule: effectiveRule,
+			limits: defaultImportLimits(), versionState: state,
+		}
+		if diagnostic := validateResolvedFilesystemDirectories(resolved); diagnostic != nil {
+			t.Fatalf("validate overlay context: %#v", diagnostic)
+		}
+		access, diagnostic := openSelectedOverlayAccess(resolved)
+		if diagnostic != nil {
+			t.Fatalf("open overlay context: %#v", diagnostic)
+		}
+		_, diagnostics = loadSelectedOverlay(request, access, assembly, sourceInfos(main.source))
 		if len(diagnostics) != 0 {
 			t.Fatalf("load selected overlay: %#v", diagnostics)
 		}