Added check for duplicate config entries

lib/config.js

@@ -42,6 +42,54 @@ function validateConfig(config) {
     throw new Error('Configuration must include at least one `apiKeys` or `serviceAccounts`');
   }
 
+  // Ensure API key values are unique when using apiKeys
+  if (hasApiKeys) {
+    const extracted = config.apiKeys.map(item => {
+      if (typeof item === 'string') return item.trim();
+      if (item && typeof item === 'object') return (item.key || item.apiKey || '').toString().trim();
+      return '';
+    });
+    const nonEmpty = extracted.filter(Boolean);
+    const unique = new Set(nonEmpty);
+    if (unique.size !== nonEmpty.length) {
+      throw new Error('`apiKeys` contains duplicate `key` values; ensure all API keys are unique');
+    }
+  }
+
+  // Ensure service account credential paths are unique when using serviceAccounts
+  if (hasSvcAccounts) {
+    // Read and canonicalize the contents of each service account credential
+    const svcContents = config.serviceAccounts.map(item => {
+      let p = '';
+      if (typeof item === 'string') p = item.trim();
+      else if (item && typeof item === 'object') p = (item.path || item.file || item.credentialsPath || '').toString().trim();
+      if (!p) return '';
+      const full = path.isAbsolute(p) ? p : path.resolve(process.cwd(), p);
+      if (!fs.existsSync(full)) {
+        throw new Error(`Service account file not found: ${p}`);
+      }
+      const raw = fs.readFileSync(full, 'utf8').trim();
+      try {
+        const parsed = JSON.parse(raw);
+        const canonicalize = (obj) => {
+          if (obj === null || typeof obj !== 'object') return JSON.stringify(obj);
+          if (Array.isArray(obj)) return '[' + obj.map(canonicalize).join(',') + ']';
+          const keys = Object.keys(obj).sort();
+          return '{' + keys.map(k => JSON.stringify(k) + ':' + canonicalize(obj[k])).join(',') + '}';
+        };
+        return canonicalize(parsed);
+      } catch (e) {
+        // Non-JSON files: use raw contents
+        return raw;
+      }
+    }).filter(Boolean);
+
+    const uniqueSvc = new Set(svcContents);
+    if (uniqueSvc.size !== svcContents.length) {
+      throw new Error('`serviceAccounts` contains duplicate credential contents; ensure all service account credentials are unique');
+    }
+  }
+
   // Basic validation of documents/sheets structure
   for (const doc of config.documents) {
     if (!doc.documentId) throw new Error('Each document must include a `documentId`');