Clear non-empty prompts with ctrl + c (#3285)

This updates the ctrl + c behavior to clear the current prompt if there
is text and you press ctrl + c.

I also updated the ctrl + c hint text to show `^c to interrupt` instead
of `^c to quit` if there is an active conversation.

Two things I don't love:
1. You can currently interrupt a conversation with escape or ctrl + c
(not related to this PR and maybe fine)
2. The bottom row hint text always says `^c to quit` but this PR doesn't
really make that worse.




https://github.com/user-attachments/assets/6eddadec-0d84-4fa7-abcb-d6f5a04e5748


Fixes https://github.com/openai/codex/issues/3126

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

@@ -79,6 +79,7 @@ pub(crate) struct ChatComposer {
     has_focus: bool,
     attached_images: Vec<AttachedImage>,
     placeholder_text: String,
+    is_task_running: bool,
     // Non-bracketed paste burst tracker.
     paste_burst: PasteBurst,
     // When true, disables paste-burst logic and inserts characters immediately.
@@ -119,6 +120,7 @@ impl ChatComposer {
             has_focus: has_input_focus,
             attached_images: Vec::new(),
             placeholder_text,
+            is_task_running: false,
             paste_burst: PasteBurst::default(),
             disable_paste_burst: false,
             custom_prompts: Vec::new(),
@@ -1205,6 +1207,10 @@ impl ChatComposer {
         self.has_focus = has_focus;
     }
 
+    pub fn set_task_running(&mut self, running: bool) {
+        self.is_task_running = running;
+    }
+
     pub(crate) fn set_esc_backtrack_hint(&mut self, show: bool) {
         self.esc_backtrack_hint = show;
     }
@@ -1229,11 +1235,16 @@ impl WidgetRef for ChatComposer {
             ActivePopup::None => {
                 let bottom_line_rect = popup_rect;
                 let mut hint: Vec<Span<'static>> = if self.ctrl_c_quit_hint {
+                    let ctrl_c_followup = if self.is_task_running {
+                        " to interrupt"
+                    } else {
+                        " to quit"
+                    };
                     vec![
                         " ".into(),
                         key_hint::ctrl('C'),
                         " again".into(),
-                        " to quit".into(),
+                        ctrl_c_followup.into(),
                     ]
                 } else {
                     let newline_hint_key = if self.use_shift_enter_hint {