fix(auth): surface 'No token' dispatch failure as AuthError::NoToken

When a session expires mid-chat, the AWS SDK returns a dispatch failure
with 'No token' in the error chain. This was converted to ChatError::Client
and displayed as an opaque multi-line error instead of the clear
'Your session has expired. Run q login' message.

Add is_no_token_error() to walk the error source chain and detect this
case, converting it to ChatError::Auth(AuthError::NoToken) so the
existing handler in handle_chat_error displays the actionable message.

Fixes #3173

Author: sandikodev

crates/chat-cli/src/cli/chat/mod.rs

@@ -624,10 +624,31 @@ impl ReasonCode for ChatError {
 
 impl From<ApiClientError> for ChatError {
     fn from(value: ApiClientError) -> Self {
+        // A dispatch failure with "No token" in the error chain means the session has
+        // expired. Surface this as AuthError::NoToken so the handler in handle_chat_error
+        // can display a clear "run `q login`" message instead of an opaque SDK error.
+        // See: #3173
+        if is_no_token_error(&value) {
+            return Self::Auth(crate::auth::AuthError::NoToken);
+        }
         Self::Client(Box::new(value))
     }
 }
 
+/// Returns true if the error chain contains a "No token" dispatch failure,
+/// which indicates the user's session has expired.
+fn is_no_token_error(err: &ApiClientError) -> bool {
+    use std::error::Error;
+    let mut source: Option<&dyn Error> = Some(err);
+    while let Some(e) = source {
+        if e.to_string().contains("No token") {
+            return true;
+        }
+        source = e.source();
+    }
+    false
+}
+
 impl From<parser::SendMessageError> for ChatError {
     fn from(value: parser::SendMessageError) -> Self {
         Self::SendMessage(Box::new(value))