diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 9ce2747823..1868f02c4d 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -131,9 +131,8 @@ use crate::skills::SkillInjections;
 use crate::skills::SkillMetadata;
 use crate::skills::SkillsManager;
 use crate::skills::build_skill_injections;
-use crate::state::ActiveTurn;
+use crate::state::AgentState;
 use crate::state::SessionServices;
-use crate::state::SessionState;
 use crate::tasks::GhostSnapshotTask;
 use crate::tasks::ReviewTask;
 use crate::tasks::SessionTask;
@@ -358,24 +357,6 @@ pub(crate) struct Session {
 ///
 /// The struct itself is stored in an `Arc`, so fields use `Mutex` to guard
 /// concurrent mutation rather than additional `Arc` layers.
-pub(crate) struct AgentState {
-    pub(crate) agent_id: AgentId,
-    /// Session configuration + conversation history for this agent.
-    state: Mutex<SessionState>,
-    /// Active turn state is tracked per-agent (each agent can have its own task).
-    pub(crate) active_turn: Mutex<Option<ActiveTurn>>,
-}
-
-impl AgentState {
-    fn new(agent_id: AgentId, session_configuration: SessionConfiguration) -> Self {
-        Self {
-            agent_id,
-            state: Mutex::new(SessionState::new(session_configuration)),
-            active_turn: Mutex::new(None),
-        }
-    }
-}
-
 /// The context needed for a single turn of the conversation.
 #[derive(Debug)]
 pub(crate) struct TurnContext {
@@ -3059,7 +3040,6 @@ mod tests {
     use crate::tools::format_exec_output_str;
     use codex_protocol::models::FunctionCallOutputPayload;
 
-    use super::AgentState;
     use crate::protocol::CompactedItem;
     use crate::protocol::CreditsSnapshot;
     use crate::protocol::DEFAULT_AGENT_ID;
@@ -3068,6 +3048,8 @@ mod tests {
     use crate::protocol::RateLimitWindow;
     use crate::protocol::ResumedHistory;
     use crate::protocol::RolloutLine;
+    use crate::state::AgentState;
+    use crate::state::SessionState;
     use crate::state::TaskKind;
     use crate::tasks::SessionTask;
     use crate::tasks::SessionTaskContext;
diff --git a/codex-rs/core/src/state/agent.rs b/codex-rs/core/src/state/agent.rs
new file mode 100644
index 0000000000..a37a5673d9
--- /dev/null
+++ b/codex-rs/core/src/state/agent.rs
@@ -0,0 +1,28 @@
+use tokio::sync::Mutex;
+
+use crate::codex::SessionConfiguration;
+use crate::state::ActiveTurn;
+use crate::state::SessionState;
+use codex_protocol::protocol::AgentId;
+
+/// Per-agent mutable state shared across async tasks.
+///
+/// The struct itself is stored in an `Arc`, so fields use `Mutex` to guard
+/// concurrent mutation rather than additional `Arc` layers.
+pub(crate) struct AgentState {
+    pub(crate) agent_id: AgentId,
+    /// Session configuration + conversation history for this agent.
+    pub(crate) state: Mutex<SessionState>,
+    /// Active turn state is tracked per-agent (each agent can have its own task).
+    pub(crate) active_turn: Mutex<Option<ActiveTurn>>,
+}
+
+impl AgentState {
+    pub(crate) fn new(agent_id: AgentId, session_configuration: SessionConfiguration) -> Self {
+        Self {
+            agent_id,
+            state: Mutex::new(SessionState::new(session_configuration)),
+            active_turn: Mutex::new(None),
+        }
+    }
+}
diff --git a/codex-rs/core/src/state/mod.rs b/codex-rs/core/src/state/mod.rs
index 642433a786..228b62034c 100644
--- a/codex-rs/core/src/state/mod.rs
+++ b/codex-rs/core/src/state/mod.rs
@@ -1,7 +1,9 @@
+mod agent;
 mod service;
 mod session;
 mod turn;
 
+pub(crate) use agent::AgentState;
 pub(crate) use service::SessionServices;
 pub(crate) use session::SessionState;
 pub(crate) use turn::ActiveTurn;