Add /compact (#1527)

- Add operation to summarize the context so far.
- The operation runs a compact task that summarizes the context.
- The operation clear the previous context to free the context window
- The operation didn't use `run_task` to avoid corrupting the session
- Add /compact in the tui



https://github.com/user-attachments/assets/e06c24e5-dcfb-4806-934a-564d425a919c

codex-rs/tui/src/app.rs

@@ -10,6 +10,8 @@ use crate::tui;
 use codex_core::config::Config;
 use codex_core::protocol::Event;
 use codex_core::protocol::EventMsg;
+use codex_core::protocol::ExecApprovalRequestEvent;
+use codex_core::protocol::Op;
 use color_eyre::eyre::Result;
 use crossterm::SynchronizedUpdate;
 use crossterm::event::KeyCode;
@@ -298,6 +300,12 @@ impl App<'_> {
                         self.app_state = AppState::Chat { widget: new_widget };
                         self.app_event_tx.send(AppEvent::RequestRedraw);
                     }
+                    SlashCommand::Compact => {
+                        if let AppState::Chat { widget } = &mut self.app_state {
+                            widget.clear_token_usage();
+                            self.app_event_tx.send(AppEvent::CodexOp(Op::Compact));
+                        }
+                    }
                     SlashCommand::Quit => {
                         break;
                     }