feat: open prompt in configured external editor (#7606)

Add `ctrl+g` shortcut to enable opening current prompt in configured
editor (`$VISUAL` or `$EDITOR`).


- Prompt is updated with editor's content upon editor close.
- Paste placeholders are automatically expanded when opening the
external editor, and are not "recompressed" on close
- They could be preserved in the editor, but it would be hard to prevent
the user from modifying the placeholder text directly, which would drop
the mapping to the `pending_paste` value
- Image placeholders stay as-is
- `ctrl+g` explanation added to shortcuts menu, snapshot tests updated



https://github.com/user-attachments/assets/4ee05c81-fa49-4e99-8b07-fc9eef0bbfce

codex-rs/tui/src/chatwidget.rs

@@ -302,6 +302,14 @@ enum RateLimitSwitchPromptState {
     Shown,
 }
 
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub(crate) enum ExternalEditorState {
+    #[default]
+    Closed,
+    Requested,
+    Active,
+}
+
 pub(crate) struct ChatWidget {
     app_event_tx: AppEventSender,
     codex_op_tx: UnboundedSender<Op>,
@@ -360,6 +368,7 @@ pub(crate) struct ChatWidget {
     feedback: codex_feedback::CodexFeedback,
     // Current session rollout path (if known)
     current_rollout_path: Option<PathBuf>,
+    external_editor_state: ExternalEditorState,
 }
 
 struct UserMessage {
@@ -1469,6 +1478,7 @@ impl ChatWidget {
             last_rendered_width: std::cell::Cell::new(None),
             feedback,
             current_rollout_path: None,
+            external_editor_state: ExternalEditorState::Closed,
         };
 
         widget.prefetch_rate_limits();
@@ -1555,6 +1565,7 @@ impl ChatWidget {
             last_rendered_width: std::cell::Cell::new(None),
             feedback,
             current_rollout_path: None,
+            external_editor_state: ExternalEditorState::Closed,
         };
 
         widget.prefetch_rate_limits();
@@ -1653,6 +1664,31 @@ impl ChatWidget {
         self.request_redraw();
     }
 
+    pub(crate) fn composer_text_with_pending(&self) -> String {
+        self.bottom_pane.composer_text_with_pending()
+    }
+
+    pub(crate) fn apply_external_edit(&mut self, text: String) {
+        self.bottom_pane.apply_external_edit(text);
+        self.request_redraw();
+    }
+
+    pub(crate) fn external_editor_state(&self) -> ExternalEditorState {
+        self.external_editor_state
+    }
+
+    pub(crate) fn set_external_editor_state(&mut self, state: ExternalEditorState) {
+        self.external_editor_state = state;
+    }
+
+    pub(crate) fn set_footer_hint_override(&mut self, items: Option<Vec<(String, String)>>) {
+        self.bottom_pane.set_footer_hint_override(items);
+    }
+
+    pub(crate) fn can_launch_external_editor(&self) -> bool {
+        self.bottom_pane.can_launch_external_editor()
+    }
+
     fn dispatch_command(&mut self, cmd: SlashCommand) {
         if !cmd.available_during_task() && self.bottom_pane.is_task_running() {
             let message = format!(
@@ -1854,7 +1890,7 @@ impl ChatWidget {
             .send(AppEvent::InsertHistoryCell(Box::new(cell)));
     }
 
-    fn add_to_history(&mut self, cell: impl HistoryCell + 'static) {
+    pub(crate) fn add_to_history(&mut self, cell: impl HistoryCell + 'static) {
         self.add_boxed_history(Box::new(cell));
     }