fix utm unicode

src/services/url/index.ts

@@ -62,17 +62,30 @@ export const getCurrentQueryParams = (): Record<string, string> => {
   return utmParams;
 };
 
+/**
+ * Convert bytes to base64 string (handles UTF-8 properly)
+ * MDN recommended approach: https://developer.mozilla.org/en-US/docs/Web/API/Window/btoa#unicode_strings
+ */
+const bytesToBase64 = (bytes: Uint8Array): string => {
+  const binString = Array.from(bytes, (byte) =>
+    String.fromCodePoint(byte)
+  ).join("");
+  return btoa(binString);
+};
+
 /**
  * Encode params as base64 JSON for state parameter
- * Uses URL-safe base64 encoding
+ * Uses URL-safe base64 encoding with UTF-8 support
+ * Handles Unicode characters (e.g., utm_campaign=夏セール)
  */
 export const encodeStateParam = (params: Record<string, string>): string => {
   if (Object.keys(params).length === 0) return "";
 
   try {
     const json = JSON.stringify(params);
-    // Use btoa for base64, replace unsafe chars for URL
-    const base64 = btoa(json)
+    // Encode string as UTF-8 bytes, then convert to base64
+    const bytes = new TextEncoder().encode(json);
+    const base64 = bytesToBase64(bytes)
       .replace(/\+/g, "-")
       .replace(/\//g, "_")
       .replace(/=+$/, "");