fix(stub): resolve TCP socket leak on target server disconnect and hanging connection attempt

mcp-stdio/src/lib.rs

@@ -22,9 +22,8 @@ pub async fn read_mcp_message<R: tokio::io::AsyncRead + Unpin>(
             break;
         }
 
-        let lower_line = line.to_lowercase();
-        if let Some(len_str) = lower_line.strip_prefix("content-length:") {
-            length = len_str.trim().parse().unwrap_or(0);
+        if line.len() >= 15 && line[..15].eq_ignore_ascii_case("content-length:") {
+            length = line[15..].trim().parse().unwrap_or(0);
         }
     }
 
@@ -39,3 +38,4 @@ pub async fn read_mcp_message<R: tokio::io::AsyncRead + Unpin>(
 
     String::from_utf8(buffer).ok()
 }
+