MAESTRO: enforce header input validation

frontend/src/lib/header-validation.ts

@@ -0,0 +1,13 @@
+export const MAX_HEADER_INPUT_BYTES = 1024 * 1024;
+
+export const validateHeaderInput = (value: string): string | null => {
+  if (value.length > MAX_HEADER_INPUT_BYTES) {
+    return "Header input exceeds the 1 MB limit.";
+  }
+
+  if (value.trim().length === 0) {
+    return "Header input cannot be empty.";
+  }
+
+  return null;
+};