Share dynamic tool specifications across turn snapshots (#55261)

## What changed

Store dynamic tool specifications in an `Arc<[DynamicToolSpec]>` so session configuration and turn snapshots share the list fixed at thread startup instead of copying it on each clone.

Keep the `dynamic_tools()` accessor returning a `Vec<DynamicToolSpec>`, but copy the specifications after releasing the session state lock.

GitOrigin-RevId: 092c5f9ea6cc390d948c27cd11340aeb12bd6037

codex-rs/core/src/session/mod.rs

@@ -950,7 +950,7 @@ impl Session {
             parent_thread_id,
             thread_source,
             originator,
-            dynamic_tools,
+            dynamic_tools: Arc::from(dynamic_tools),
             user_shell_override,
         };
         session_configuration

codex-rs/core/src/session/session.rs

@@ -163,7 +163,8 @@ pub(crate) struct SessionConfiguration {
     pub(super) thread_source: Option<ThreadSource>,
     /// Effective originator used for this thread's Responses requests and analytics events.
     pub(super) originator: String,
-    pub(super) dynamic_tools: Vec<DynamicToolSpec>,
+    /// Fixed at thread startup and shared with turn snapshots.
+    pub(super) dynamic_tools: Arc<[DynamicToolSpec]>,
     pub(super) user_shell_override: Option<shell::Shell>,
 }
 
@@ -678,8 +679,11 @@ impl Session {
     }
 
     pub(crate) async fn dynamic_tools(&self) -> Vec<DynamicToolSpec> {
-        let state = self.state.lock().await;
-        state.session_configuration.dynamic_tools.clone()
+        let dynamic_tools = {
+            let state = self.state.lock().await;
+            Arc::clone(&state.session_configuration.dynamic_tools)
+        };
+        dynamic_tools.to_vec()
     }
 
     pub(crate) async fn responses_metadata(
@@ -1066,7 +1070,7 @@ impl Session {
                                 text: session_configuration.base_instructions.clone(),
                                 provenance: base_instructions_provenance.clone(),
                             },
-                            dynamic_tools: session_configuration.dynamic_tools.clone(),
+                            dynamic_tools: session_configuration.dynamic_tools.to_vec(),
                             selected_capability_roots: selected_capability_roots.clone(),
                             multi_agent_version: initial_multi_agent_version,
                             history_mode: session_configuration.history_mode,

codex-rs/core/src/session/tests.rs

@@ -4516,7 +4516,7 @@ async fn set_rate_limits_retains_previous_credits() {
         parent_thread_id: None,
         thread_source: None,
         originator: "test_originator".to_string(),
-        dynamic_tools: Vec::new(),
+        dynamic_tools: Arc::default(),
         user_shell_override: None,
     };
 
@@ -4639,7 +4639,7 @@ async fn set_rate_limits_updates_plan_type_when_present() {
         parent_thread_id: None,
         thread_source: None,
         originator: "test_originator".to_string(),
-        dynamic_tools: Vec::new(),
+        dynamic_tools: Arc::default(),
         user_shell_override: None,
     };
 
@@ -5263,7 +5263,7 @@ pub(crate) async fn make_session_configuration_for_tests() -> SessionConfigurati
         parent_thread_id: None,
         thread_source: None,
         originator: "test_originator".to_string(),
-        dynamic_tools: Vec::new(),
+        dynamic_tools: Arc::default(),
         user_shell_override: None,
     }
 }
@@ -6836,7 +6836,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         parent_thread_id: None,
         thread_source: None,
         originator: "test_originator".to_string(),
-        dynamic_tools: Vec::new(),
+        dynamic_tools: Arc::default(),
         user_shell_override: None,
     };
     let session_telemetry = session_telemetry(
@@ -7156,7 +7156,7 @@ async fn make_session_with_config_and_rx(
         parent_thread_id: None,
         thread_source: None,
         originator: "test_originator".to_string(),
-        dynamic_tools: Vec::new(),
+        dynamic_tools: Arc::default(),
         user_shell_override: None,
     };
 
@@ -7291,7 +7291,7 @@ async fn make_session_with_history_source_and_agent_control_and_rx(
         parent_thread_id: None,
         thread_source: None,
         originator: "test_originator".to_string(),
-        dynamic_tools: Vec::new(),
+        dynamic_tools: Arc::default(),
         user_shell_override: None,
     };
 
@@ -9104,7 +9104,7 @@ where
         parent_thread_id: None,
         thread_source: None,
         originator: "test_originator".to_string(),
-        dynamic_tools,
+        dynamic_tools: Arc::from(dynamic_tools),
         user_shell_override: None,
     };
     let session_telemetry = session_telemetry(

codex-rs/core/src/session/turn_context.rs

@@ -368,7 +368,7 @@ pub struct TurnContext {
     pub(crate) windows_sandbox_level: WindowsSandboxLevel,
     pub(crate) available_models: Vec<ModelPreset>,
     pub(crate) final_output_json_schema: Option<Value>,
-    pub(crate) dynamic_tools: Vec<DynamicToolSpec>,
+    pub(crate) dynamic_tools: Arc<[DynamicToolSpec]>,
     pub(crate) turn_metadata_state: Arc<TurnMetadataState>,
     pub(crate) extension_data: Arc<codex_extension_api::ExtensionData>,
     pub(crate) turn_timing_state: Arc<TurnTimingState>,