diff --git a/codex-rs/core/src/conversation_manager.rs b/codex-rs/core/src/conversation_manager.rs
index a30038f2eb..dbf2a1850f 100644
--- a/codex-rs/core/src/conversation_manager.rs
+++ b/codex-rs/core/src/conversation_manager.rs
@@ -32,8 +32,34 @@ pub struct NewConversation {
 
 /// [`ConversationManager`] is responsible for creating conversations and
 /// maintaining them in memory.
+#[derive(Clone)]
+struct ConversationEntry {
+    conversation: Arc<CodexConversation>,
+    session_configured: SessionConfiguredEvent,
+}
+
+impl ConversationEntry {
+    fn new(
+        conversation: Arc<CodexConversation>,
+        session_configured: SessionConfiguredEvent,
+    ) -> Self {
+        Self {
+            conversation,
+            session_configured,
+        }
+    }
+
+    fn to_new_conversation(&self, conversation_id: ConversationId) -> NewConversation {
+        NewConversation {
+            conversation_id,
+            conversation: self.conversation.clone(),
+            session_configured: self.session_configured.clone(),
+        }
+    }
+}
+
 pub struct ConversationManager {
-    conversations: Arc<RwLock<HashMap<ConversationId, Arc<CodexConversation>>>>,
+    conversations: Arc<RwLock<HashMap<ConversationId, ConversationEntry>>>,
     auth_manager: Arc<AuthManager>,
     session_source: SessionSource,
 }
@@ -99,10 +125,11 @@ impl ConversationManager {
         };
 
         let conversation = Arc::new(CodexConversation::new(codex));
+        let entry = ConversationEntry::new(conversation.clone(), session_configured.clone());
         self.conversations
             .write()
             .await
-            .insert(conversation_id, conversation.clone());
+            .insert(conversation_id, entry);
 
         Ok(NewConversation {
             conversation_id,
@@ -118,7 +145,7 @@ impl ConversationManager {
         let conversations = self.conversations.read().await;
         conversations
             .get(&conversation_id)
-            .cloned()
+            .map(|entry| entry.conversation.clone())
             .ok_or_else(|| CodexErr::ConversationNotFound(conversation_id))
     }
 
@@ -129,11 +156,22 @@ impl ConversationManager {
         auth_manager: Arc<AuthManager>,
     ) -> CodexResult<NewConversation> {
         let initial_history = RolloutRecorder::get_rollout_history(&rollout_path).await?;
-        let CodexSpawnOk {
-            codex,
-            conversation_id,
-        } = Codex::spawn(config, auth_manager, initial_history, self.session_source).await?;
-        self.finalize_spawn(codex, conversation_id).await
+        if let InitialHistory::Resumed(resumed) = &initial_history
+            && let Some(existing) = self
+                .conversations
+                .read()
+                .await
+                .get(&resumed.conversation_id)
+                .cloned()
+        {
+            Ok(existing.to_new_conversation(resumed.conversation_id))
+        } else {
+            let CodexSpawnOk {
+                codex,
+                conversation_id,
+            } = Codex::spawn(config, auth_manager, initial_history, self.session_source).await?;
+            self.finalize_spawn(codex, conversation_id).await
+        }
     }
 
     /// Removes the conversation from the manager's internal map, though the
@@ -144,7 +182,11 @@ impl ConversationManager {
         &self,
         conversation_id: &ConversationId,
     ) -> Option<Arc<CodexConversation>> {
-        self.conversations.write().await.remove(conversation_id)
+        self.conversations
+            .write()
+            .await
+            .remove(conversation_id)
+            .map(|entry| entry.conversation)
     }
 
     /// Fork an existing conversation by taking messages up to the given position
diff --git a/codex-rs/core/src/default_client.rs b/codex-rs/core/src/default_client.rs
index 8e4635460c..deefb50a5d 100644
--- a/codex-rs/core/src/default_client.rs
+++ b/codex-rs/core/src/default_client.rs
@@ -288,7 +288,9 @@ mod tests {
     #[test]
     fn test_get_codex_user_agent() {
         let user_agent = get_codex_user_agent();
-        assert!(user_agent.starts_with("codex_cli_rs/"));
+        let originator = originator();
+        let expected_prefix = format!("{}/", originator.value.as_str());
+        assert!(user_agent.starts_with(expected_prefix.as_str()));
     }
 
     #[tokio::test]
@@ -366,10 +368,12 @@ mod tests {
     fn test_macos() {
         use regex_lite::Regex;
         let user_agent = get_codex_user_agent();
-        let re = Regex::new(
-            r"^codex_cli_rs/\d+\.\d+\.\d+ \(Mac OS \d+\.\d+\.\d+; (x86_64|arm64)\) (\S+)$",
-        )
-        .unwrap();
+        let originator = originator();
+        let originator_pattern = regex_lite::escape(originator.value.as_str());
+        let pattern = format!(
+            r"^{originator_pattern}/\d+\.\d+\.\d+ \(Mac OS \d+\.\d+\.\d+; (x86_64|arm64)\) (\S+)$"
+        );
+        let re = Regex::new(pattern.as_str()).unwrap();
         assert!(re.is_match(&user_agent));
     }
 }
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index 8730f1f38f..f27d2adfb0 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -247,7 +247,11 @@ async fn resume_includes_initial_messages_and_sends_prior_items() {
         session_configured,
         ..
     } = conversation_manager
-        .resume_conversation_from_rollout(config, session_path.clone(), auth_manager)
+        .resume_conversation_from_rollout(
+            config.clone(),
+            session_path.clone(),
+            auth_manager.clone(),
+        )
         .await
         .expect("resume conversation");
 
@@ -260,6 +264,23 @@ async fn resume_includes_initial_messages_and_sends_prior_items() {
     let expected_initial_json = json!([]);
     assert_eq!(initial_json, expected_initial_json);
 
+    let NewConversation {
+        conversation: codex_again,
+        session_configured: session_configured_again,
+        ..
+    } = conversation_manager
+        .resume_conversation_from_rollout(
+            config.clone(),
+            session_path.clone(),
+            auth_manager.clone(),
+        )
+        .await
+        .expect("resume existing conversation");
+    assert!(Arc::ptr_eq(&codex, &codex_again));
+    let session_configured_json = serde_json::to_value(&session_configured).unwrap();
+    let session_configured_again_json = serde_json::to_value(&session_configured_again).unwrap();
+    assert_eq!(session_configured_json, session_configured_again_json);
+
     // 2) Submit new input; the request body must include the prior item followed by the new user input.
     codex
         .submit(Op::UserInput {