diff --git a/codex-rs/core/src/agent/control/spawn.rs b/codex-rs/core/src/agent/control/spawn.rs
index 1de4768e65..553f9977e8 100644
--- a/codex-rs/core/src/agent/control/spawn.rs
+++ b/codex-rs/core/src/agent/control/spawn.rs
@@ -17,6 +17,7 @@ struct SpawnAgentThreadInheritance {
 /// submission and lifecycle logging cannot receive one without the other. Other spawn sources
 /// provide user input directly, making an uncontextualized inter-agent communication
 /// unrepresentable.
+#[allow(clippy::large_enum_variant)]
 enum SpawnInitialInput {
     UserInput(Vec<UserInput>),
     InterAgentCommunication(InterAgentCommunication, AgentCommunicationContext),
diff --git a/codex-rs/core/src/agent/control_tests.rs b/codex-rs/core/src/agent/control_tests.rs
index df13e1bf66..9ea2e4fa37 100644
--- a/codex-rs/core/src/agent/control_tests.rs
+++ b/codex-rs/core/src/agent/control_tests.rs
@@ -1477,6 +1477,7 @@ async fn spawn_agent_can_fork_parent_thread_history_with_sanitized_items() {
         ThreadHistoryMode::Legacy
     );
     let history = child_thread.session.clone_history().await;
+    let history_items = history.raw_items().cloned().collect::<Vec<_>>();
     let mut expected_final_answer =
         assistant_message("parent final answer", Some(MessagePhase::FinalAnswer));
     expected_final_answer.set_turn_id_if_missing(&turn_context.sub_id);
@@ -1496,6 +1497,12 @@ async fn spawn_agent_can_fork_parent_thread_history_with_sanitized_items() {
         internal_chat_message_metadata_passthrough: None,
     };
     expected_developer_message.set_turn_id_if_missing(&turn_context.sub_id);
+    expected_developer_message.set_create_time_if_missing(
+        history_items[1]
+            .executed_tool_call_metadata()
+            .and_then(|metadata| metadata.create_time.clone())
+            .expect("recorded developer message should have a creation timestamp"),
+    );
     let expected_history = [
         expected_parent_seed,
         expected_developer_message,
@@ -1510,7 +1517,6 @@ async fn spawn_agent_can_fork_parent_thread_history_with_sanitized_items() {
             internal_chat_message_metadata_passthrough: None,
         },
     ];
-    let history_items = history.raw_items().cloned().collect::<Vec<_>>();
     assert_eq!(
         strip_response_item_ids(&history_items),
         strip_response_item_ids(&expected_history),
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index 51aa3d6d18..8d54232fd9 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -2948,6 +2948,20 @@ impl Session {
         }
     }
 
+    pub(crate) fn response_item_create_time() -> serde_json::Number {
+        let create_time = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .unwrap_or_default();
+        serde_json::Number::from_f64(create_time.as_secs_f64())
+            .unwrap_or_else(|| serde_json::Number::from(create_time.as_secs()))
+    }
+
+    /// Adds the turn ID and creation time to newly created conversation items.
+    pub(crate) fn stamp_response_item_for_history(item: &mut ResponseItem, turn_id: &str) {
+        item.set_turn_id_if_missing(turn_id);
+        item.set_create_time_if_missing(Self::response_item_create_time());
+    }
+
     /// Records conversation items: append to history, persist to rollout, and
     /// notify clients observing raw response items.
     pub(crate) fn prepare_conversation_items_for_history<'a>(
@@ -2981,7 +2995,7 @@ impl Session {
         prepare_audio_response_items(&mut items);
         // Most response items get their passthrough turn ID at the durable history boundary.
         for item in &mut items {
-            item.set_turn_id_if_missing(&turn_context.sub_id);
+            Self::stamp_response_item_for_history(item, &turn_context.sub_id);
         }
         let items = Cow::Owned(items);
         (
@@ -3223,9 +3237,8 @@ impl Session {
     pub(crate) async fn record_inter_agent_communication(
         &self,
         turn_context: &TurnContext,
-        mut communication: InterAgentCommunication,
+        communication: InterAgentCommunication,
     ) {
-        communication.set_turn_id_if_missing(&turn_context.sub_id);
         let response_item = communication.to_model_input_item();
         let (items, _) = self.prepare_conversation_items_for_history(
             turn_context,
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index 3fe765c75e..f360f5c6f0 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -2085,13 +2085,23 @@ async fn record_conversation_items_stamps_missing_turn_id_and_preserves_existing
         .record_conversation_items(&turn_context, &[fresh_item.clone(), existing_item.clone()])
         .await;
 
+    let history = session.clone_history().await;
+    let recorded_items = raw_history_items(&history);
+    let fresh_create_time = recorded_items[0]
+        .executed_tool_call_metadata()
+        .and_then(|metadata| metadata.create_time.clone())
+        .expect("harness-authored items should receive creation timestamps");
+    assert!(
+        fresh_create_time
+            .as_f64()
+            .is_some_and(|seconds| seconds > 0.0)
+    );
+
     let mut expected_fresh_item = fresh_item;
     expected_fresh_item.set_turn_id_if_missing(&turn_context.sub_id);
+    expected_fresh_item.set_create_time_if_missing(fresh_create_time);
     let expected_items = vec![expected_fresh_item, existing_item];
-    assert_eq!(
-        raw_history_items(&session.clone_history().await),
-        expected_items
-    );
+    assert_eq!(recorded_items, expected_items);
 }
 
 #[tokio::test]
@@ -2191,8 +2201,17 @@ async fn record_inter_agent_communication_sets_turn_id_in_rollout_and_resume() {
         .record_inter_agent_communication(&turn_context, communication)
         .await;
 
+    let recorded_history = session.clone_history().await;
+    let recorded_items = raw_history_items(&recorded_history);
+    let create_time = recorded_items[0]
+        .executed_tool_call_metadata()
+        .and_then(|metadata| metadata.create_time.clone())
+        .expect("locally authored agent message should receive a creation timestamp");
+    assert!(create_time.as_f64().is_some_and(|seconds| seconds > 0.0));
+    expected_item.set_create_time_if_missing(create_time);
+
     assert_eq!(
-        strip_response_item_ids(&raw_history_items(&session.clone_history().await)),
+        strip_response_item_ids(&recorded_items),
         strip_response_item_ids(std::slice::from_ref(&expected_item))
     );
 
@@ -2564,8 +2583,10 @@ async fn resumed_history_injects_initial_context_on_first_context_update_only()
     expected.extend(initial_context);
     let history_after_seed = session.clone_history().await;
     assert_eq!(
-        strip_response_item_ids(&expected),
-        strip_response_item_ids(&raw_history_items(&history_after_seed))
+        strip_response_item_ids(&strip_metadata_from_items(&expected)),
+        strip_response_item_ids(&strip_metadata_from_items(&raw_history_items(
+            &history_after_seed
+        )))
     );
 
     session
@@ -9606,8 +9627,8 @@ async fn record_context_updates_and_set_reference_context_item_injects_full_cont
     let history = session.clone_history().await;
     let initial_context = build_initial_context(&session, &turn_context).await;
     assert_eq!(
-        strip_response_item_ids(&raw_history_items(&history)),
-        strip_response_item_ids(&initial_context)
+        strip_response_item_ids(&strip_metadata_from_items(&raw_history_items(&history))),
+        strip_response_item_ids(&strip_metadata_from_items(&initial_context))
     );
 
     let current_context = session.reference_context_item().await;
@@ -9661,8 +9682,8 @@ async fn record_context_updates_and_set_reference_context_item_reinjects_full_co
     let initial_context = build_initial_context(&session, &turn_context).await;
     expected_history.extend(initial_context);
     assert_eq!(
-        strip_response_item_ids(&raw_history_items(&history)),
-        strip_response_item_ids(&expected_history)
+        strip_response_item_ids(&strip_metadata_from_items(&raw_history_items(&history))),
+        strip_response_item_ids(&strip_metadata_from_items(&expected_history))
     );
 }
 
diff --git a/codex-rs/core/src/tools/handlers/extension_tools.rs b/codex-rs/core/src/tools/handlers/extension_tools.rs
index eae4622576..af137cb777 100644
--- a/codex-rs/core/src/tools/handlers/extension_tools.rs
+++ b/codex-rs/core/src/tools/handlers/extension_tools.rs
@@ -382,8 +382,15 @@ mod tests {
         session
             .record_conversation_items(&turn, std::slice::from_ref(&history_item))
             .await;
-        let mut expected_history_item = history_item.clone();
-        expected_history_item.set_turn_id_if_missing(&turn_id);
+        let expected_history_item = strip_response_item_id(
+            session
+                .clone_history()
+                .await
+                .raw_items()
+                .next()
+                .expect("history item")
+                .clone(),
+        );
         let raw_history_event = rx.recv().await.expect("history raw response item event");
         let EventMsg::RawResponseItem(raw_history_item) = raw_history_event.msg else {
             panic!("expected raw response item event");
diff --git a/codex-rs/core/src/tools/router_tests.rs b/codex-rs/core/src/tools/router_tests.rs
index f354c75475..f763ca266d 100644
--- a/codex-rs/core/src/tools/router_tests.rs
+++ b/codex-rs/core/src/tools/router_tests.rs
@@ -545,8 +545,13 @@ async fn extension_tool_executors_are_model_visible_and_dispatchable() -> anyhow
     session
         .record_conversation_items(&turn, std::slice::from_ref(&history_item))
         .await;
-    let mut expected_history_item = history_item.clone();
-    expected_history_item.set_turn_id_if_missing(&turn.sub_id);
+    let expected_history_item = session
+        .clone_history()
+        .await
+        .raw_items()
+        .next()
+        .expect("history item")
+        .clone();
 
     let router = test_tool_router(
         step_context.as_ref(),
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index 30751b3bd7..6f6f30962d 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -196,12 +196,17 @@ fn assert_codex_client_metadata(
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn openai_stateless_responses_requests_preserve_item_turn_metadata_across_turns() {
     let server = MockServer::start().await;
+    let assistant_create_time = 1_785_276_138.422709;
+    let mut assistant_message = ev_assistant_message("msg-1", "first answer");
+    assistant_message["item"]["internal_chat_message_metadata_passthrough"] = json!({
+        "create_time": assistant_create_time,
+    });
     let response_mock = mount_sse_sequence(
         &server,
         vec![
             sse(vec![
                 ev_response_created("resp1"),
-                ev_assistant_message("msg-1", "first answer"),
+                assistant_message,
                 ev_completed("resp1"),
             ]),
             sse(vec![ev_response_created("resp2"), ev_completed("resp2")]),
@@ -234,6 +239,14 @@ async fn openai_stateless_responses_requests_preserve_item_turn_metadata_across_
             Some(first_turn_id)
         );
     }
+    for role in ["user", "developer"] {
+        assert!(first_input.iter().any(|item| {
+            item["role"].as_str() == Some(role)
+                && item["internal_chat_message_metadata_passthrough"]["create_time"]
+                    .as_f64()
+                    .is_some_and(|create_time| create_time > 0.0)
+        }));
+    }
 
     let item_turn_id = |text: &str| {
         second_input
@@ -250,6 +263,26 @@ async fn openai_stateless_responses_requests_preserve_item_turn_metadata_across_
     assert_eq!(item_turn_id("turn one"), Some(first_turn_id));
     assert_eq!(item_turn_id("first answer"), Some(first_turn_id));
     assert_eq!(item_turn_id("turn two"), Some(second_turn_id));
+
+    let item_create_time = |text: &str| {
+        second_input
+            .iter()
+            .find(|item| {
+                item["content"].as_array().is_some_and(|content| {
+                    content
+                        .iter()
+                        .any(|content_item| content_item["text"].as_str() == Some(text))
+                })
+            })
+            .and_then(|item| {
+                item["internal_chat_message_metadata_passthrough"]["create_time"].as_f64()
+            })
+    };
+    assert_eq!(
+        item_create_time("first answer"),
+        Some(assistant_create_time)
+    );
+    assert!(item_create_time("turn two").is_some_and(|create_time| create_time > 0.0));
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
diff --git a/codex-rs/core/tests/suite/compact_remote.rs b/codex-rs/core/tests/suite/compact_remote.rs
index df641a6be8..7d7acca203 100644
--- a/codex-rs/core/tests/suite/compact_remote.rs
+++ b/codex-rs/core/tests/suite/compact_remote.rs
@@ -1380,6 +1380,27 @@ async fn remote_compact_v2_reuses_compaction_trigger_for_followups() -> Result<(
 
     let response_requests = responses_mock.requests();
     let compact_request = &response_requests[2];
+    let item_create_time = |request: &responses::ResponsesRequest, text: &str| {
+        request
+            .input()
+            .into_iter()
+            .find(|item| {
+                item["content"].as_array().is_some_and(|content| {
+                    content.iter().any(|part| {
+                        part["text"].as_str() == Some(text)
+                            || part["encrypted_content"].as_str() == Some(text)
+                    })
+                })
+            })
+            .and_then(|item| {
+                item.pointer("/internal_chat_message_metadata_passthrough/create_time")
+                    .cloned()
+            })
+            .expect("matching message should include a creation timestamp")
+    };
+    let original_user_create_time = item_create_time(&response_requests[0], "hello remote compact");
+    let delegated_task_create_time =
+        item_create_time(&response_requests[1], &delegated_task_ciphertext);
     assert!(
         compact_request
             .inputs_of_type("agent_message")
@@ -1444,6 +1465,19 @@ async fn remote_compact_v2_reuses_compaction_trigger_for_followups() -> Result<(
     );
 
     let follow_up_request = response_requests.last().expect("follow-up request missing");
+    assert_eq!(
+        item_create_time(follow_up_request, "hello remote compact"),
+        original_user_create_time
+    );
+    assert_eq!(
+        item_create_time(follow_up_request, &delegated_task_ciphertext),
+        delegated_task_create_time
+    );
+    assert!(
+        item_create_time(follow_up_request, "after compact")
+            .as_f64()
+            .is_some_and(|create_time| create_time > 0.0)
+    );
     assert!(
         follow_up_request
             .inputs_of_type("agent_message")
diff --git a/codex-rs/core/tests/suite/tools.rs b/codex-rs/core/tests/suite/tools.rs
index bcb8e464f1..2374220d7c 100644
--- a/codex-rs/core/tests/suite/tools.rs
+++ b/codex-rs/core/tests/suite/tools.rs
@@ -409,10 +409,15 @@ async fn namespaced_custom_tool_call_preserves_namespace_through_dispatch_and_re
         .and_then(Value::as_str)
         .map(str::to_string)
         .expect("custom tool call should include turn metadata");
+    let custom_tool_output = request.custom_tool_call_output(call_id);
+    let output_create_time = custom_tool_output
+        .pointer("/internal_chat_message_metadata_passthrough/create_time")
+        .and_then(Value::as_f64)
+        .expect("custom tool output should include a creation timestamp");
     assert_eq!(
         (
             strip_response_item_ids_from_json(Value::Array(custom_tool_calls)),
-            strip_response_item_ids_from_json(request.custom_tool_call_output(call_id)),
+            strip_response_item_ids_from_json(custom_tool_output),
         ),
         (
             Value::Array(vec![json!({
@@ -431,6 +436,7 @@ async fn namespaced_custom_tool_call_preserves_namespace_through_dispatch_and_re
                 "output": format!("unsupported custom tool call: {namespace}{tool_name}"),
                 "internal_chat_message_metadata_passthrough": {
                     "turn_id": turn_id,
+                    "create_time": output_create_time,
                     "executed_tool_calls": [{
                         "name": format!("{namespace}__{tool_name}"),
                         "arguments": input,
diff --git a/codex-rs/protocol/src/models.rs b/codex-rs/protocol/src/models.rs
index 4ea9cd1c23..851f738778 100644
--- a/codex-rs/protocol/src/models.rs
+++ b/codex-rs/protocol/src/models.rs
@@ -790,6 +790,11 @@ pub struct InternalChatMessageMetadataPassthrough {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     #[ts(optional)]
     pub turn_id: Option<String>,
+    /// Message creation time in fractional Unix seconds.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[schemars(skip)]
+    #[ts(skip)]
+    pub create_time: Option<serde_json::Number>,
     /// Warehouse-only Responses metadata, not part of the public app-server protocol.
     #[serde(default, skip_deserializing, skip_serializing_if = "Option::is_none")]
     #[schemars(skip)]
@@ -1133,6 +1138,39 @@ impl ResponseItem {
         InternalChatMessageMetadataPassthrough::set_turn_id_if_missing(metadata, turn_id);
     }
 
+    /// Stamps a harness-authored durable item without replacing its creation time.
+    pub fn set_create_time_if_missing(&mut self, create_time: serde_json::Number) {
+        let metadata = match self {
+            Self::Message {
+                role,
+                internal_chat_message_metadata_passthrough: metadata,
+                ..
+            } if matches!(role.as_str(), "user" | "developer") => metadata,
+            Self::AgentMessage {
+                internal_chat_message_metadata_passthrough: metadata,
+                ..
+            }
+            | Self::FunctionCallOutput {
+                internal_chat_message_metadata_passthrough: metadata,
+                ..
+            }
+            | Self::CustomToolCallOutput {
+                internal_chat_message_metadata_passthrough: metadata,
+                ..
+            }
+            | Self::ToolSearchOutput {
+                internal_chat_message_metadata_passthrough: metadata,
+                ..
+            } => metadata,
+            _ => return,
+        };
+
+        metadata
+            .get_or_insert_default()
+            .create_time
+            .get_or_insert(create_time);
+    }
+
     /// Removes internal chat message metadata passthrough before sending to a provider that does
     /// not accept it.
     pub fn clear_internal_chat_message_metadata_passthrough(&mut self) {
@@ -2357,9 +2395,19 @@ mod tests {
         let mut missing_turn_id = response_item_with_passthrough_metadata(
             /*internal_chat_message_metadata_passthrough*/ None,
         );
+        let create_time = serde_json::Number::from(123);
+        missing_turn_id.set_create_time_if_missing(create_time.clone());
         missing_turn_id.set_turn_id_if_missing("");
         missing_turn_id.set_turn_id_if_missing("turn-1");
-        assert_eq!(missing_turn_id.turn_id(), Some("turn-1"));
+        missing_turn_id.set_create_time_if_missing(serde_json::Number::from(456));
+        assert_eq!(
+            missing_turn_id.executed_tool_call_metadata(),
+            Some(&InternalChatMessageMetadataPassthrough {
+                turn_id: Some("turn-1".to_string()),
+                create_time: Some(create_time),
+                ..Default::default()
+            })
+        );
 
         let mut other = ResponseItem::Other;
         other.set_turn_id_if_missing("turn-1");