feat: ctrl-d only exits when there is no user input (#1589)

While this does make it so that `ctrl-d` will not exit Codex when the
composer is not empty, `ctrl-d` will still exit Codex if it is in the
"working" state.

Fixes https://github.com/openai/codex/issues/1443.

codex-rs/tui/src/chatwidget.rs

@@ -432,6 +432,10 @@ impl ChatWidget<'_> {
         }
     }
 
+    pub(crate) fn composer_is_empty(&self) -> bool {
+        self.bottom_pane.composer_is_empty()
+    }
+
     /// Forward an `Op` directly to codex.
     pub(crate) fn submit_op(&self, op: Op) {
         if let Err(e) = self.codex_op_tx.send(op) {