[feat] use experimental reasoning summary (#3071)

<img width="1512" height="442" alt="Screenshot 2025-09-02 at 3 49 46 PM"
src="https://github.com/user-attachments/assets/26c3c1cf-b7ed-4520-a12a-8d38a8e0c318"
/>

codex-rs/core/src/config.rs

@@ -185,6 +185,8 @@ pub struct Config {
     /// All characters are inserted as they are received, and no buffering
     /// or placeholder replacement will occur for fast keypress bursts.
     pub disable_paste_burst: bool,
+
+    pub use_experimental_reasoning_summary: bool,
 }
 
 impl Config {
@@ -482,6 +484,8 @@ pub struct ConfigToml {
 
     pub experimental_use_exec_command_tool: Option<bool>,
 
+    pub use_experimental_reasoning_summary: Option<bool>,
+
     /// The value for the `originator` header included with Responses API requests.
     pub responses_originator_header_internal_override: Option<String>,
 
@@ -807,6 +811,9 @@ impl Config {
                 .unwrap_or(false),
             include_view_image_tool,
             disable_paste_burst: cfg.disable_paste_burst.unwrap_or(false),
+            use_experimental_reasoning_summary: cfg
+                .use_experimental_reasoning_summary
+                .unwrap_or(false),
         };
         Ok(config)
     }
@@ -1177,6 +1184,7 @@ disable_response_storage = true
                 use_experimental_streamable_shell_tool: false,
                 include_view_image_tool: true,
                 disable_paste_burst: false,
+                use_experimental_reasoning_summary: false,
             },
             o3_profile_config
         );
@@ -1235,6 +1243,7 @@ disable_response_storage = true
             use_experimental_streamable_shell_tool: false,
             include_view_image_tool: true,
             disable_paste_burst: false,
+            use_experimental_reasoning_summary: false,
         };
 
         assert_eq!(expected_gpt3_profile_config, gpt3_profile_config);
@@ -1308,6 +1317,7 @@ disable_response_storage = true
             use_experimental_streamable_shell_tool: false,
             include_view_image_tool: true,
             disable_paste_burst: false,
+            use_experimental_reasoning_summary: false,
         };
 
         assert_eq!(expected_zdr_profile_config, zdr_profile_config);

codex-rs/tui/src/chatwidget.rs

@@ -191,10 +191,12 @@ impl ChatWidget {
         // At the end of a reasoning block, record transcript-only content.
         self.full_reasoning_buffer.push_str(&self.reasoning_buffer);
         if !self.full_reasoning_buffer.is_empty() {
-            self.add_to_history(history_cell::new_reasoning_block(
+            for cell in history_cell::new_reasoning_summary_block(
                 self.full_reasoning_buffer.clone(),
                 &self.config,
-            ));
+            ) {
+                self.add_boxed_history(cell);
+            }
         }
         self.reasoning_buffer.clear();
         self.full_reasoning_buffer.clear();
@@ -900,16 +902,14 @@ impl ChatWidget {
     }
 
     fn add_to_history(&mut self, cell: impl HistoryCell + 'static) {
+        self.add_boxed_history(Box::new(cell));
+    }
+
+    fn add_boxed_history(&mut self, cell: Box<dyn HistoryCell>) {
         if !cell.display_lines(u16::MAX).is_empty() {
             // Only break exec grouping if the cell renders visible lines.
             self.flush_active_exec_cell();
         }
-        self.app_event_tx
-            .send(AppEvent::InsertHistoryCell(Box::new(cell)));
-    }
-
-    fn add_boxed_history(&mut self, cell: Box<dyn HistoryCell>) {
-        self.flush_active_exec_cell();
         self.app_event_tx.send(AppEvent::InsertHistoryCell(cell));
     }
 

codex-rs/tui/src/history_cell.rs

@@ -1247,6 +1247,44 @@ pub(crate) fn new_reasoning_block(
     TranscriptOnlyHistoryCell { lines }
 }
 
+pub(crate) fn new_reasoning_summary_block(
+    full_reasoning_buffer: String,
+    config: &Config,
+) -> Vec<Box<dyn HistoryCell>> {
+    if config.use_experimental_reasoning_summary {
+        // Experimental format is following:
+        // ** header **
+        //
+        // reasoning summary
+        //
+        // So we need to strip header from reasoning summary
+        if let Some(open) = full_reasoning_buffer.find("**") {
+            let after_open = &full_reasoning_buffer[(open + 2)..];
+            if let Some(close) = after_open.find("**") {
+                let after_close_idx = open + 2 + close + 2;
+                let header_buffer = full_reasoning_buffer[..after_close_idx].to_string();
+                let summary_buffer = full_reasoning_buffer[after_close_idx..].to_string();
+
+                let mut header_lines: Vec<Line<'static>> = Vec::new();
+                header_lines.push(Line::from("Thinking".magenta().italic()));
+                append_markdown(&header_buffer, &mut header_lines, config);
+
+                let mut summary_lines: Vec<Line<'static>> = Vec::new();
+                summary_lines.push(Line::from("Thinking".magenta().bold()));
+                append_markdown(&summary_buffer, &mut summary_lines, config);
+
+                return vec![
+                    Box::new(TranscriptOnlyHistoryCell {
+                        lines: header_lines,
+                    }),
+                    Box::new(AgentMessageCell::new(summary_lines, true)),
+                ];
+            }
+        }
+    }
+    vec![Box::new(new_reasoning_block(full_reasoning_buffer, config))]
+}
+
 fn output_lines(
     output: Option<&CommandOutput>,
     only_err: bool,