show diff output in the pager (#2568)

this shows `/diff` output in an overlay like the transcript, instead of
dumping it into history.



https://github.com/user-attachments/assets/48e79b65-7f66-45dd-97b3-d5c627ac7349

codex-rs/tui/src/app.rs

@@ -5,6 +5,7 @@ use crate::file_search::FileSearchManager;
 use crate::transcript_app::TranscriptApp;
 use crate::tui;
 use crate::tui::TuiEvent;
+use codex_ansi_escape::ansi_escape_line;
 use codex_core::ConversationManager;
 use codex_core::config::Config;
 use codex_core::protocol::TokenUsage;
@@ -17,6 +18,7 @@ use crossterm::terminal::EnterAlternateScreen;
 use crossterm::terminal::LeaveAlternateScreen;
 use crossterm::terminal::supports_keyboard_enhancement;
 use ratatui::layout::Rect;
+use ratatui::style::Stylize;
 use ratatui::text::Line;
 use std::path::PathBuf;
 use std::sync::Arc;
@@ -126,8 +128,8 @@ impl App {
                     tui.insert_history_lines(lines);
                 }
                 self.transcript_overlay = None;
+                tui.frame_requester().schedule_frame();
             }
-            tui.frame_requester().schedule_frame();
         } else {
             match event {
                 TuiEvent::Key(key_event) => {
@@ -238,7 +240,29 @@ impl App {
             }
             AppEvent::CodexOp(op) => self.chat_widget.submit_op(op),
             AppEvent::DiffResult(text) => {
-                self.chat_widget.add_diff_output(text);
+                // Clear the in-progress state in the bottom pane
+                self.chat_widget.on_diff_complete();
+
+                // Enter alternate screen and set viewport to full size.
+                let _ = execute!(tui.terminal.backend_mut(), EnterAlternateScreen);
+                if let Ok(size) = tui.terminal.size() {
+                    self.transcript_saved_viewport = Some(tui.terminal.viewport_area);
+                    tui.terminal
+                        .set_viewport_area(Rect::new(0, 0, size.width, size.height));
+                    let _ = tui.terminal.clear();
+                }
+
+                // Build pager lines directly without the "/diff" header
+                let pager_lines: Vec<ratatui::text::Line<'static>> = if text.trim().is_empty() {
+                    vec!["No changes detected.".italic().into()]
+                } else {
+                    text.lines().map(ansi_escape_line).collect()
+                };
+                self.transcript_overlay = Some(TranscriptApp::with_title(
+                    pager_lines,
+                    "D I F F".to_string(),
+                ));
+                tui.frame_requester().schedule_frame();
             }
             AppEvent::StartFileSearch(query) => {
                 if !query.is_empty() {

codex-rs/tui/src/chatwidget.rs

@@ -818,9 +818,8 @@ impl ChatWidget {
         self.request_redraw();
     }
 
-    pub(crate) fn add_diff_output(&mut self, diff_output: String) {
+    pub(crate) fn on_diff_complete(&mut self) {
         self.bottom_pane.set_task_running(false);
-        self.add_to_history(history_cell::new_diff_output(diff_output));
         self.mark_needs_redraw();
     }
 

codex-rs/tui/src/history_cell.rs

@@ -506,20 +506,6 @@ pub(crate) fn new_completed_mcp_tool_call(
     Box::new(PlainHistoryCell { lines })
 }
 
-pub(crate) fn new_diff_output(message: String) -> PlainHistoryCell {
-    let mut lines: Vec<Line<'static>> = Vec::new();
-    lines.push(Line::from("/diff".magenta()));
-
-    if message.trim().is_empty() {
-        lines.push(Line::from("No changes detected.".italic()));
-    } else {
-        lines.extend(message.lines().map(ansi_escape_line));
-    }
-
-    lines.push(Line::from(""));
-    PlainHistoryCell { lines }
-}
-
 pub(crate) fn new_status_output(
     config: &Config,
     usage: &TokenUsage,

codex-rs/tui/src/transcript_app.rs

@@ -21,6 +21,7 @@ pub(crate) struct TranscriptApp {
     pub(crate) transcript_lines: Vec<Line<'static>>,
     pub(crate) scroll_offset: usize,
     pub(crate) is_done: bool,
+    title: String,
 }
 
 impl TranscriptApp {
@@ -29,6 +30,16 @@ impl TranscriptApp {
             transcript_lines,
             scroll_offset: 0,
             is_done: false,
+            title: "T R A N S C R I P T".to_string(),
+        }
+    }
+
+    pub(crate) fn with_title(transcript_lines: Vec<Line<'static>>, title: String) -> Self {
+        Self {
+            transcript_lines,
+            scroll_offset: 0,
+            is_done: false,
+            title,
         }
     }
 
@@ -114,8 +125,11 @@ impl TranscriptApp {
             } => {
                 self.scroll_offset = usize::MAX;
             }
-            _ => {}
+            _ => {
+                return;
+            }
         }
+        tui.frame_requester().schedule_frame();
     }
 
     fn scroll_area(&self, area: Rect) -> Rect {
@@ -130,9 +144,8 @@ impl TranscriptApp {
         Span::from("/ ".repeat(area.width as usize / 2))
             .dim()
             .render_ref(area, buf);
-        Span::from("/ T R A N S C R I P T")
+        let header = format!("/ {}", self.title);
-            .dim()
+        Span::from(header).dim().render_ref(area, buf);
-            .render_ref(area, buf);
 
         // Main content area (excludes header and bottom status section)
         let content_area = self.scroll_area(area);