[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);