diff --git a/src/cmd.rs b/src/cmd.rs
index d15441c..9b6bbbc 100644
--- a/src/cmd.rs
+++ b/src/cmd.rs
@@ -610,18 +610,20 @@ async fn rpush_cmd(server: &Server, key: &str, elements: &[String]) -> Result<Pr
 }
 
 async fn exec_cmd(server: &mut Server) -> Result<Protocol, DBError> {
+    // Move the queued commands out of `server` so we drop the borrow immediately.
     let cmds = if let Some(cmds) = server.queued_cmd.take() {
         cmds
     } else {
         return Ok(Protocol::err("ERR EXEC without MULTI"));
     };
 
-    let mut vec = Vec::new();
+    let mut out = Vec::new();
     for (cmd, _) in cmds {
-        let res = cmd.run(server).await?;
-        vec.push(res);
+        // Use Box::pin to handle recursion in async function
+        let res = Box::pin(cmd.run(server)).await?;
+        out.push(res);
     }
-    Ok(Protocol::Array(vec))
+    Ok(Protocol::Array(out))
 }
 
 async fn incr_cmd(server: &Server, key: &String) -> Result<Protocol, DBError> {
@@ -835,26 +837,39 @@ async fn hsetnx_cmd(server: &Server, key: &str, field: &str, value: &str) -> Res
     }
 }
 
-async fn scan_cmd(server: &Server, cursor: &u64, pattern: Option<&str>, count: &Option<u64>) -> Result<Protocol, DBError> {
-    server.current_storage()?.scan(*cursor, pattern, *count).map(|(next_cursor, keys)| {
-        let mut result = Vec::new();
-        result.push(Protocol::BulkString(next_cursor.to_string()));
-        result.push(Protocol::Array(
-            keys.into_iter().map(Protocol::BulkString).collect(),
-        ));
-        Protocol::Array(result)
-    })
+async fn scan_cmd(
+    server: &Server,
+    cursor: &u64,
+    pattern: Option<&str>,
+    count: &Option<u64>
+) -> Result<Protocol, DBError> {
+    match server.current_storage()?.scan(*cursor, pattern, *count) {
+        Ok((next_cursor, keys)) => {
+            let mut result = Vec::new();
+            result.push(Protocol::BulkString(next_cursor.to_string()));
+            result.push(Protocol::Array(keys.into_iter().map(Protocol::BulkString).collect()));
+            Ok(Protocol::Array(result))
+        }
+        Err(e) => Ok(Protocol::err(&format!("ERR {}", e.0))),
+    }
 }
 
-async fn hscan_cmd(server: &Server, key: &str, cursor: &u64, pattern: Option<&str>, count: &Option<u64>) -> Result<Protocol, DBError> {
-    server.current_storage()?.hscan(key, *cursor, pattern, *count).map(|(next_cursor, fields)| {
-        let mut result = Vec::new();
-        result.push(Protocol::BulkString(next_cursor.to_string()));
-        result.push(Protocol::Array(
-            fields.into_iter().map(Protocol::BulkString).collect(),
-        ));
-        Protocol::Array(result)
-    })
+async fn hscan_cmd(
+    server: &Server,
+    key: &str,
+    cursor: &u64,
+    pattern: Option<&str>,
+    count: &Option<u64>
+) -> Result<Protocol, DBError> {
+    match server.current_storage()?.hscan(key, *cursor, pattern, *count) {
+        Ok((next_cursor, fields)) => {
+            let mut result = Vec::new();
+            result.push(Protocol::BulkString(next_cursor.to_string()));
+            result.push(Protocol::Array(fields.into_iter().map(Protocol::BulkString).collect()));
+            Ok(Protocol::Array(result))
+        }
+        Err(e) => Ok(Protocol::err(&format!("ERR {}", e.0))),
+    }
 }
 
 async fn ttl_cmd(server: &Server, key: &str) -> Result<Protocol, DBError> {
diff --git a/src/protocol.rs b/src/protocol.rs
index ad42309..c9a2255 100644
--- a/src/protocol.rs
+++ b/src/protocol.rs
@@ -8,6 +8,7 @@ pub enum Protocol {
     BulkString(String),
     Null,
     Array(Vec<Protocol>),
+    Error(String), // NEW
 }
 
 impl fmt::Display for Protocol {
@@ -45,7 +46,7 @@ impl Protocol {
 
     #[inline]
     pub fn err(msg: &str) -> Self {
-        Protocol::SimpleString(msg.to_string())
+        Protocol::Error(msg.to_string())
     }
 
     #[inline]
@@ -69,22 +70,19 @@ impl Protocol {
             Protocol::BulkString(s) => s.to_string(),
             Protocol::Null => "".to_string(),
             Protocol::Array(s) => s.iter().map(|x| x.decode()).collect::<Vec<_>>().join(" "),
+            Protocol::Error(s) => s.to_string(),
         }
     }
 
     pub fn encode(&self) -> String {
         match self {
             Protocol::SimpleString(s) => format!("+{}\r\n", s),
-            Protocol::BulkString(s) => format!("${}\r\n{}\r\n", s.len(), s),
-            Protocol::Array(ss) => {
-                format!("*{}\r\n", ss.len())
-                    + ss.iter()
-                        .map(|x| x.encode())
-                        .collect::<Vec<_>>()
-                        .join("")
-                        .as_str()
+            Protocol::BulkString(s)   => format!("${}\r\n{}\r\n", s.len(), s),
+            Protocol::Array(ss)       => {
+                format!("*{}\r\n", ss.len()) + &ss.iter().map(|x| x.encode()).collect::<String>()
             }
-            Protocol::Null => "$-1\r\n".to_string(),
+            Protocol::Null            => "$-1\r\n".to_string(),
+            Protocol::Error(s)        => format!("-{}\r\n", s), // proper RESP error
         }
     }
 
diff --git a/src/server.rs b/src/server.rs
index 6a389af..8d294b0 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -97,7 +97,15 @@ impl Server {
                 // Check if this is a QUIT command before processing
                 let is_quit = matches!(cmd, Cmd::Quit);
 
-                let res = cmd.run(self).await.unwrap_or(Protocol::err("unknown cmd from server"));
+                let res = match cmd.run(self).await {
+                    Ok(p) => p,
+                    Err(e) => {
+                        if self.option.debug {
+                            eprintln!("[run error] {:?}", e);
+                        }
+                        Protocol::err(&format!("ERR {}", e.0))
+                    }
+                };
                 
                 if self.option.debug {
                     println!("\x1b[34;1mqueued cmd {:?}\x1b[0m", self.queued_cmd);