Bug fix: ignore Enter on empty input to avoid queuing blank messages (#3047)

## Summary
Pressing Enter with an empty composer was treated as a submission, which
queued a blank message while a task was running. This PR suppresses
submission when there is no text and no attachments.

## Root Cause

- ChatComposer returned Submitted even when the trimmed text was empty.
ChatWidget then queued it during a running task, leading to an empty
item appearing in the queued list and being popped later with no effect.

## Changes
- ChatComposer Enter handling: if trimmed text is empty and there are no
attached images, return None instead of Submitted.
- No changes to ChatWidget; behavior naturally stops queuing blanks at
the source.

## Code Paths

- Modified: `tui/src/bottom_pane/chat_composer.rs`
- Tests added:
    - `tui/src/bottom_pane/chat_composer.rs`: `empty_enter_returns_none`
- `tui/src/chatwidget/tests.rs`:
`empty_enter_during_task_does_not_queue`

## Result

### Before


https://github.com/user-attachments/assets/a40e2f6d-42ba-4a82-928b-8f5458f5884d

### After



https://github.com/user-attachments/assets/958900b7-a566-44fc-b16c-b80380739c92

codex-rs/tui/src/bottom_pane/chat_composer.rs

@@ -837,7 +837,12 @@ impl ChatComposer {
                 }
                 self.pending_pastes.clear();
 
+                // If there is neither text nor attachments, suppress submission entirely.
+                let has_attachments = !self.attached_images.is_empty();
                 text = text.trim().to_string();
+                if text.is_empty() && !has_attachments {
+                    return (InputResult::None, true);
+                }
                 if !text.is_empty() {
                     self.history.record_local_submission(&text);
                 }
@@ -1520,6 +1525,33 @@ mod tests {
         }
     }
 
+    #[test]
+    fn empty_enter_returns_none() {
+        use crossterm::event::KeyCode;
+        use crossterm::event::KeyEvent;
+        use crossterm::event::KeyModifiers;
+
+        let (tx, _rx) = unbounded_channel::<AppEvent>();
+        let sender = AppEventSender::new(tx);
+        let mut composer = ChatComposer::new(
+            true,
+            sender,
+            false,
+            "Ask Codex to do anything".to_string(),
+            false,
+        );
+
+        // Ensure composer is empty and press Enter.
+        assert!(composer.textarea.text().is_empty());
+        let (result, _needs_redraw) =
+            composer.handle_key_event(KeyEvent::new(KeyCode::Enter, KeyModifiers::NONE));
+
+        match result {
+            InputResult::None => {}
+            other => panic!("expected None for empty enter, got: {other:?}"),
+        }
+    }
+
     #[test]
     fn handle_paste_large_uses_placeholder_and_replaces_on_submit() {
         use crossterm::event::KeyCode;

codex-rs/tui/src/chatwidget/tests.rs

@@ -259,6 +259,20 @@ fn open_fixture(name: &str) -> std::fs::File {
     File::open(name).expect("open fixture file")
 }
 
+#[test]
+fn empty_enter_during_task_does_not_queue() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual();
+
+    // Simulate running task so submissions would normally be queued.
+    chat.bottom_pane.set_task_running(true);
+
+    // Press Enter with an empty composer.
+    chat.handle_key_event(KeyEvent::new(KeyCode::Enter, KeyModifiers::NONE));
+
+    // Ensure nothing was queued.
+    assert!(chat.queued_user_messages.is_empty());
+}
+
 #[test]
 fn alt_up_edits_most_recent_queued_message() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual();