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;
                     }

codex-rs/tui/src/chatwidget.rs

@@ -502,6 +502,12 @@ impl ChatWidget<'_> {
     pub(crate) fn token_usage(&self) -> &TokenUsage {
         &self.token_usage
     }
+
+    pub(crate) fn clear_token_usage(&mut self) {
+        self.token_usage = TokenUsage::default();
+        self.bottom_pane
+            .set_token_usage(self.token_usage.clone(), self.config.model_context_window);
+    }
 }
 
 impl WidgetRef for &ChatWidget<'_> {

codex-rs/tui/src/slash_command.rs

@@ -13,6 +13,7 @@ pub enum SlashCommand {
     // DO NOT ALPHA-SORT! Enum order is presentation order in the popup, so
     // more frequently used commands should be listed first.
     New,
+    Compact,
     Diff,
     Quit,
     #[cfg(debug_assertions)]
@@ -24,6 +25,7 @@ impl SlashCommand {
     pub fn description(self) -> &'static str {
         match self {
             SlashCommand::New => "Start a new chat.",
+            SlashCommand::Compact => "Compact the chat history.",
             SlashCommand::Quit => "Exit the application.",
             SlashCommand::Diff => {
                 "Show git diff of the working directory (including untracked files)"