milestone 20: declarative configuration for iac

web/src/features/settings/ReadOnlyConfigBanner.tsx

@@ -0,0 +1,19 @@
+import { useAuthority } from "./authority";
+
+/**
+ * File authority is a standing condition, not an event, so this banner has no
+ * dismiss button: it stays up for as long as the process runs from a file.
+ */
+export default function ReadOnlyConfigBanner() {
+	const authority = useAuthority();
+	if (authority?.mode !== "managed_file") return null;
+	return (
+		<div
+			role="status"
+			className="border-b border-amber-300 bg-amber-50 px-4 py-2 text-sm text-amber-900 dark:border-amber-800 dark:bg-amber-950 dark:text-amber-100"
+		>
+			Configuration is managed by <code className="font-mono">{authority.path}</code>. Edit the file and restart
+			nxdns to change it; the server rejects edits made here.
+		</div>
+	);
+}