Keep interrupted prompts in conversation history (#33198)

## What changed

- Leave an output-free interrupted prompt in the transcript and open a blank
  composer for the user's next instruction.
- Use the normal interruption notice for both `Esc` and `Ctrl-C` interrupts.
- Track safety-buffering prompts separately so failed retries can still restore
  the prompt, including after switching between threads.

## Testing

- Cover output-free `Esc` and `Ctrl-C` interrupts, failed safety-buffer retries,
  and restoration of safety-buffer state from thread snapshots.

GitOrigin-RevId: 30b368d00dfdb981d06d4c95ce3f252389b7917c

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

@@ -199,7 +199,7 @@ impl ChatWidget {
             forked_from: None,
             interrupted_turn_notice_mode: InterruptedTurnNoticeMode::Default,
             input_queue: InputQueueState::default(),
-            cancel_edit: CancelEditState::default(),
+            safety_buffering_prompt: None,
             chat_keymap,
             queued_message_edit_hint_binding,
             show_welcome_banner: is_first_run,