Preserve empty user turns during contextual stripping

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/compact_tests.rs

@@ -150,6 +150,35 @@ fn collect_user_messages_filters_ephemeral_context_entries() {
     assert_eq!(vec!["real user message".to_string()], collected);
 }
 
+#[test]
+fn collect_user_messages_preserves_empty_user_turns() {
+    let items = vec![
+        ResponseItem::Message {
+            id: None,
+            role: "user".to_string(),
+            content: Vec::new(),
+            end_turn: None,
+            phase: None,
+        },
+        ResponseItem::Message {
+            id: None,
+            role: "user".to_string(),
+            content: vec![ContentItem::InputText {
+                text: "real user message".to_string(),
+            }],
+            end_turn: None,
+            phase: None,
+        },
+    ];
+
+    let collected = collect_user_messages(&items);
+
+    assert_eq!(
+        vec![String::new(), "real user message".to_string()],
+        collected
+    );
+}
+
 #[test]
 fn build_token_limited_compacted_history_truncates_overlong_user_messages() {
     // Use a small truncation limit so the test remains fast while still validating

codex-rs/core/src/event_mapping.rs

@@ -32,14 +32,15 @@ fn strip_ephemeral_context_prefix(message: &[ContentItem]) -> &[ContentItem] {
 
 pub(crate) fn is_contextual_user_message_content(message: &[ContentItem]) -> bool {
     let stripped = strip_ephemeral_context_prefix(message);
-    stripped.is_empty() || stripped.iter().any(is_contextual_user_fragment)
+    (stripped.len() != message.len() && stripped.is_empty())
+        || stripped.iter().any(is_contextual_user_fragment)
 }
 
 fn parse_user_message(message: &[ContentItem]) -> Option<UserMessageItem> {
-    let message = strip_ephemeral_context_prefix(message);
     if is_contextual_user_message_content(message) {
         return None;
     }
+    let message = strip_ephemeral_context_prefix(message);
 
     let mut content: Vec<UserInput> = Vec::new();
 

codex-rs/core/src/event_mapping_tests.rs

@@ -263,6 +263,23 @@ fn drops_user_message_when_only_ephemeral_context_prefix_is_present() {
     assert!(parse_turn_item(&item).is_none());
 }
 
+#[test]
+fn parses_empty_user_message_as_user_turn() {
+    let item = ResponseItem::Message {
+        id: None,
+        role: "user".to_string(),
+        content: Vec::new(),
+        end_turn: None,
+        phase: None,
+    };
+
+    let turn_item = parse_turn_item(&item).expect("expected empty user message turn item");
+    let TurnItem::UserMessage(user_message) = turn_item else {
+        panic!("expected TurnItem::UserMessage");
+    };
+    assert_eq!(user_message.content, Vec::<UserInput>::new());
+}
+
 #[test]
 fn parses_agent_message() {
     let item = ResponseItem::Message {