feat: add native Windows hierarchy test harness

internal/client/supervisor/windows/testfaults_default.go

@@ -0,0 +1,15 @@
+//go:build !rvbox_native_test
+
+package windows
+
+import "fmt"
+
+// NativeTestContextFailures is intentionally unavailable in shipped binaries.
+// The native fixture compiles a separately tagged test executable when it
+// needs to prove a pre-launch fallback row.
+func NativeTestContextFailures(raw string) (map[ExecutionContext]bool, error) {
+	if raw != "" {
+		return nil, fmt.Errorf("--test-fail-contexts requires the rvbox_native_test fixture build")
+	}
+	return nil, nil
+}