refactor: Extract shared MCP Stdio NDJSON parsing loop into mcp-stdio library

stub/src/main.rs

@@ -12,40 +12,7 @@ struct Cli {
     target: String,
 }
 
-async fn read_mcp_message(stdin: &mut tokio::io::BufReader<tokio::io::Stdin>) -> Option<String> {
-    use tokio::io::AsyncReadExt;
-    let mut length = 0;
-    loop {
-        let mut line = String::new();
-        let bytes_read = stdin.read_line(&mut line).await.unwrap_or(0);
-        if bytes_read == 0 {
-            tracing::info!("stdin EOF reached");
-            return None;
-        }
-        tracing::info!("Read {} bytes from stdin: {:?}", bytes_read, line);
 
-        if line.starts_with('{') {
-            return Some(line.trim_end().to_string());
-        }
-
-        let line = line.trim_end();
-        if line.is_empty() {
-            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 length == 0 {
-        return None;
-    }
-    let mut buffer = vec![0; length];
-    if stdin.read_exact(&mut buffer).await.is_err() {
-        return None;
-    }
-    String::from_utf8(buffer).ok()
-}
 
 fn init_logging(app_name: &str) -> Option<tracing_appender::non_blocking::WorkerGuard> {
     let mut base_dir = dirs::home_dir().unwrap_or_else(|| std::path::PathBuf::from("."));
@@ -74,7 +41,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
 
         tokio::spawn(async move {
             let mut stdin = tokio::io::BufReader::new(tokio::io::stdin());
-            while let Some(msg) = read_mcp_message(&mut stdin).await {
+            while let Some(msg) = mcp_stdio::read_mcp_message(&mut stdin).await {
                 let _ = msg_tx.send(msg).await;
             }
             let _ = shutdown_tx.send(()).await;
@@ -190,3 +157,4 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         Ok(())
     })
 }
+