diff --git a/codex-rs/core/src/agent/control.rs b/codex-rs/core/src/agent/control.rs
index 5253ed41b7..6ef9c31d7f 100644
--- a/codex-rs/core/src/agent/control.rs
+++ b/codex-rs/core/src/agent/control.rs
@@ -260,20 +260,13 @@ impl LocalAgentControl {
         &self,
         agent_id: ThreadId,
         state: &Arc<ThreadManagerState>,
-        mut communication: InterAgentCommunication,
+        communication: InterAgentCommunication,
         context: AgentCommunicationContext,
         start_options: TurnStartOptions,
     ) -> CodexResult<String> {
         let observers = state.extensions.message_lifecycle_contributors();
-        let delivery = (!observers.is_empty()).then(|| {
-            let message_id = communication
-                .id
-                .take()
-                .filter(|id| !id.is_empty())
-                .unwrap_or_else(|| (self.runtime.item_id_generator)("amsg"));
-            communication.id = Some(message_id.clone());
-            MessageDelivery::publish(context.sender_thread_id, message_id, observers)
-        });
+        let delivery = (!observers.is_empty())
+            .then(|| MessageDelivery::publish(context.sender_thread_id, observers));
         let log_content = crate::agent_communication::send_log_content(&communication);
         {
             // Keep unloaded delivery atomic with publication of a reloaded session.
diff --git a/codex-rs/core/src/agent_communication.rs b/codex-rs/core/src/agent_communication.rs
index 0b5c8dbffa..141737c50d 100644
--- a/codex-rs/core/src/agent_communication.rs
+++ b/codex-rs/core/src/agent_communication.rs
@@ -4,7 +4,6 @@
 use codex_extension_api::ExtensionData;
 use codex_extension_api::MessageLifecycleContributor;
 use codex_extension_api::MessageLifecycleInput;
-use codex_protocol::ResponseItemId;
 use codex_protocol::ThreadId;
 use codex_protocol::protocol::InterAgentCommunication;
 use serde::Deserialize;
@@ -156,13 +155,11 @@ pub(crate) struct MessageDelivery(Arc<Mutex<Option<MessagePublication>>>);
 impl MessageDelivery {
     pub(crate) fn publish(
         sender: ThreadId,
-        message_id: ResponseItemId,
         observers: &[Arc<dyn MessageLifecycleContributor>],
     ) -> Self {
         let input = MessageLifecycleInput {
             sender,
-            data: ExtensionData::new(message_id.to_string()),
-            message_id,
+            data: ExtensionData::new(uuid::Uuid::now_v7().to_string()),
         };
         for observer in observers {
             observer.on_publish(&input);
diff --git a/codex-rs/core/tests/suite/agent_mailbox.rs b/codex-rs/core/tests/suite/agent_mailbox.rs
index a06ff09414..7fa6a3d646 100644
--- a/codex-rs/core/tests/suite/agent_mailbox.rs
+++ b/codex-rs/core/tests/suite/agent_mailbox.rs
@@ -7,7 +7,6 @@ use codex_core::config::Config;
 use codex_extension_api::ExtensionRegistryBuilder;
 use codex_extension_api::MessageLifecycleContributor;
 use codex_extension_api::MessageLifecycleInput;
-use codex_protocol::ResponseItemId;
 use codex_protocol::ThreadId;
 use codex_protocol::protocol::AgentStatus;
 use codex_protocol::protocol::Op;
@@ -20,15 +19,18 @@ use std::sync::mpsc;
 use tokio::sync::oneshot;
 
 #[derive(Default)]
-struct Messages(Mutex<HashSet<ResponseItemId>>);
+struct Messages(Mutex<HashSet<uuid::Uuid>>);
 impl MessageLifecycleContributor for Messages {
     fn on_publish(&self, input: &MessageLifecycleInput) {
         let mut pending = self.0.lock().expect("messages lock");
-        assert!(pending.insert(input.message_id.clone()));
+        let token = uuid::Uuid::new_v4();
+        input.data.insert(token);
+        assert!(pending.insert(token));
     }
     fn on_consumed(&self, input: &MessageLifecycleInput, _recipient: ThreadId) {
         let mut pending = self.0.lock().expect("messages lock");
-        assert!(pending.remove(&input.message_id));
+        let token = input.data.remove::<uuid::Uuid>().expect("published token");
+        assert!(pending.remove(token.as_ref()));
     }
 }
 
diff --git a/codex-rs/ext/extension-api/src/message_lifecycle.rs b/codex-rs/ext/extension-api/src/message_lifecycle.rs
index 85d3e169e9..dbe844a4a6 100644
--- a/codex-rs/ext/extension-api/src/message_lifecycle.rs
+++ b/codex-rs/ext/extension-api/src/message_lifecycle.rs
@@ -1,12 +1,11 @@
 //! Capture publication state once; consume it independently for each delivery.
 
 use crate::ExtensionData;
-use codex_protocol::ResponseItemId;
 use codex_protocol::ThreadId;
 
 /// State shared by all deliveries of a publication, including recipients resolved later.
+/// The model-visible item ID may still be unknown until the recipient records the message.
 pub struct MessageLifecycleInput {
-    pub message_id: ResponseItemId,
     pub sender: ThreadId,
     /// Capture contributor-specific state at publication; read it at consumption.
     pub data: ExtensionData,