chore: improve passport post to relayer error message

Author: nattb8

packages/passport/sdk/src/zkEvm/relayerClient.ts

@@ -120,7 +120,16 @@ export class RelayerClient {
       body: JSON.stringify(body),
     });
 
-    const jsonResponse = await response.json();
+    const responseText = await response.text();
+    let jsonResponse;
+    try {
+      jsonResponse = JSON.parse(responseText);
+    } catch (parseError) {
+      const preview = responseText.length > 100
+        ? `${responseText.substring(0, 50)}...${responseText.substring(responseText.length - 50)}`
+        : responseText;
+      throw new Error(`Relayer JSON parse error: ${parseError instanceof Error ? parseError.message : 'Unknown error'}. Content: "${preview}"`);
+    }
     if (jsonResponse.error) {
       throw jsonResponse.error;
     }