chore: ignore synthetic messages (#10394)

This will be fixed once this is settled:
https://www.notion.so/openai/Artificial-context-management-2fb8e50b62b080db8b8ed93b3b19d1a2#2fb8e50b62b080d2bffce2dd1e60972b

codex-rs/core/src/rollout/list.rs

@@ -15,7 +15,9 @@ use uuid::Uuid;
 
 use super::ARCHIVED_SESSIONS_SUBDIR;
 use super::SESSIONS_SUBDIR;
+use crate::instructions::UserInstructions;
 use crate::protocol::EventMsg;
+use crate::session_prefix::is_session_prefix_content;
 use crate::state_db;
 use codex_file_search as file_search;
 use codex_protocol::ThreadId;
@@ -982,9 +984,12 @@ async fn read_head_summary(path: &Path, head_limit: usize) -> io::Result<HeadTai
                     .created_at
                     .clone()
                     .or_else(|| Some(rollout_line.timestamp.clone()));
-                if let codex_protocol::models::ResponseItem::Message { role, .. } = &item
+                if let codex_protocol::models::ResponseItem::Message { role, content, .. } = &item
                     && role == "user"
+                    && !UserInstructions::is_user_instructions(content.as_slice())
+                    && !is_session_prefix_content(content.as_slice())
                 {
+                    tracing::warn!("Item: {item:#?}");
                     summary.saw_user_event = true;
                 }
                 if summary.head.len() < head_limit

codex-rs/core/src/session_prefix.rs

@@ -1,3 +1,5 @@
+use codex_protocol::models::ContentItem;
+
 /// Helpers for identifying model-visible "session prefix" messages.
 ///
 /// A session prefix is a user-role message that carries configuration or state needed by
@@ -13,3 +15,12 @@ pub(crate) fn is_session_prefix(text: &str) -> bool {
     let lowered = trimmed.to_ascii_lowercase();
     lowered.starts_with(ENVIRONMENT_CONTEXT_OPEN_TAG) || lowered.starts_with(TURN_ABORTED_OPEN_TAG)
 }
+
+/// Returns true if `text` starts with a session prefix marker (case-insensitive).
+pub(crate) fn is_session_prefix_content(content: &[ContentItem]) -> bool {
+    if let [ContentItem::InputText { text }] = content {
+        is_session_prefix(text)
+    } else {
+        false
+    }
+}