fix(json/comments): validateJSONArrayFile 先驗證再寫入避免毀損原檔、findingRow 對空值防呆

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/json.js

@@ -107,8 +107,10 @@ export async function validateJSONArrayFile(fullPath, label, repairer = repairJS
     try {
       const original = readJSONText(fullPath, label);
       const repaired = await repairer(fullPath, label, original);
-      fs.writeFileSync(fullPath, repaired.endsWith('\n') ? repaired : `${repaired}\n`, 'utf8');
-      JSON.parse(readJSONText(fullPath, label));
+      const normalized = repaired.endsWith('\n') ? repaired : `${repaired}\n`;
+      // 先驗證修復結果是否為合法 JSON；無效就在寫檔前丟出，避免用毀損內容覆寫原檔。
+      JSON.parse(normalized);
+      fs.writeFileSync(fullPath, normalized, 'utf8');
       ok(`${label} 已由 AI 修正並通過再次驗證`);
       return { exists: true, valid: true, repaired: true };
     } catch (repairErr) {