diff --git a/server/age-os/mcp-server/cos.js b/server/age-os/mcp-server/cos.js
index a3dcf5a4..2fd336ce 100644
--- a/server/age-os/mcp-server/cos.js
+++ b/server/age-os/mcp-server/cos.js
@@ -251,6 +251,23 @@ async function head(bucket, key) {
   };
 }
 
+/**
+ * 从响应头解析文件总大小（content-range 或 content-length）
+ */
+function parseTotalSize(headers) {
+  // content-range 格式: bytes 0-1023/665000000
+  const range = headers['content-range'];
+  if (range) {
+    const parts = range.split('/');
+    if (parts.length === 2) {
+      const size = parseInt(parts[1], 10);
+      if (!isNaN(size)) return size;
+    }
+  }
+  const cl = parseInt(headers['content-length'] || '0', 10);
+  return isNaN(cl) ? 0 : cl;
+}
+
 /**
  * 分块读取大文件 — 仅读取前 N 字节用于预览/采样
  * 适用于超大语料文件的类型检测和内容预览
@@ -286,8 +303,7 @@ async function readPartial(bucket, key, maxBytes) {
       res.on('end', () => {
         try {
           const buffer = Buffer.concat(chunks);
-          const totalSize = parseInt(res.headers['content-range']?.split('/')[1] || '0', 10)
-            || parseInt(res.headers['content-length'] || '0', 10);
+          const totalSize = parseTotalSize(res.headers);
           resolve({
             content: buffer.toString('utf8'),
             size_bytes: buffer.length,
@@ -303,8 +319,7 @@ async function readPartial(bucket, key, maxBytes) {
         if (chunks.length > 0) {
           try {
             const buffer = Buffer.concat(chunks);
-            const totalSize = parseInt(res.headers['content-range']?.split('/')[1] || '0', 10)
-              || parseInt(res.headers['content-length'] || '0', 10);
+            const totalSize = parseTotalSize(res.headers);
             resolve({
               content: buffer.toString('utf8'),
               size_bytes: buffer.length,
diff --git a/server/age-os/mcp-server/tools/corpus-extractor-ops.js b/server/age-os/mcp-server/tools/corpus-extractor-ops.js
index a00386a8..a001eeb4 100644
--- a/server/age-os/mcp-server/tools/corpus-extractor-ops.js
+++ b/server/age-os/mcp-server/tools/corpus-extractor-ops.js
@@ -172,8 +172,12 @@ async function cosExtractCorpus(input) {
   try {
     const meta = await cos.head(bucket, key);
     fileSize = meta.size_bytes;
-  } catch {
-    // HEAD 不支持时跳过，由后续读取处理
+  } catch (headErr) {
+    // HEAD失败不阻断流程（部分COS配置不支持HEAD），用0继续
+    // 但如果是认证/桶不存在等严重错误，后续read也会失败
+    if (headErr.message && !headErr.message.includes('405') && !headErr.message.includes('403')) {
+      console.log(`  ⚠️ HEAD预检失败: ${headErr.message}，继续尝试读取`);
+    }
   }
 
   // ZIP文件始终返回提示（无论大小），因为需要二进制解析