chore: compact do not modify instructions (#4088)

Keep the developer instruction and insert the summarisation message as a
user message instead

codex-rs/core/src/codex.rs

@@ -1117,16 +1117,13 @@ impl AgentTask {
         turn_context: Arc<TurnContext>,
         sub_id: String,
         input: Vec<InputItem>,
-        compact_instructions: String,
     ) -> Self {
         let handle = {
             let sess = sess.clone();
             let sub_id = sub_id.clone();
             let tc = Arc::clone(&turn_context);
-            tokio::spawn(async move {
-                compact::run_compact_task(sess, tc, sub_id, input, compact_instructions).await
-            })
-            .abort_handle()
+            tokio::spawn(async move { compact::run_compact_task(sess, tc, sub_id, input).await })
+                .abort_handle()
         };
         Self {
             sess,
@@ -1434,7 +1431,7 @@ async fn submission_loop(
                 // Attempt to inject input into current task
                 if let Err(items) = sess
                     .inject_input(vec![InputItem::Text {
-                        text: compact::COMPACT_TRIGGER_TEXT.to_string(),
+                        text: compact::SUMMARIZATION_PROMPT.to_string(),
                     }])
                     .await
                 {