From a1a0d9dea52dc32f57f5efd3f7fe2b67c9f3cf9a Mon Sep 17 00:00:00 2001
From: Sayan Sisodiya <sayan@openai.com>
Date: Mon, 6 Jul 2026 17:02:08 -0400
Subject: [PATCH] core: reuse MCP tool snapshot within a step

---
 codex-rs/core/src/session/step_context.rs | 11 +++++++++++
 codex-rs/core/src/session/turn.rs         |  8 ++++----
 codex-rs/core/src/session/world_state.rs  |  4 ++--
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/codex-rs/core/src/session/step_context.rs b/codex-rs/core/src/session/step_context.rs
index 3210eb028662..1d7316d91443 100644
--- a/codex-rs/core/src/session/step_context.rs
+++ b/codex-rs/core/src/session/step_context.rs
@@ -5,6 +5,8 @@ use crate::environment_selection::TurnEnvironmentSnapshot;
 use crate::session::McpRuntimeSnapshot;
 use crate::session::turn_context::TurnContext;
 use codex_exec_server::ResolvedSelectedCapabilityRoot;
+use codex_mcp::ToolInfo;
+use tokio::sync::OnceCell;
 
 /// Request-scoped state that may change between model sampling requests.
 #[derive(Debug)]
@@ -15,6 +17,8 @@ pub(crate) struct StepContext {
     pub(crate) selected_capability_roots: Vec<ResolvedSelectedCapabilityRoot>,
     /// The exact MCP config and manager used to advertise and execute tools for this step.
     pub(crate) mcp: Arc<McpRuntimeSnapshot>,
+    /// The fixed MCP tool list used for this exact sampling request.
+    mcp_tool_snapshot: OnceCell<Vec<ToolInfo>>,
     /// The canonical AGENTS.md value observed with this environment snapshot.
     pub(crate) loaded_agents_md: Option<Arc<LoadedAgentsMd>>,
 }
@@ -32,7 +36,14 @@ impl StepContext {
             environments,
             selected_capability_roots,
             mcp,
+            mcp_tool_snapshot: OnceCell::new(),
             loaded_agents_md,
         }
     }
+
+    pub(crate) async fn mcp_tools(&self) -> &[ToolInfo] {
+        self.mcp_tool_snapshot
+            .get_or_init(|| self.mcp.manager().list_all_tools())
+            .await
+    }
 }
diff --git a/codex-rs/core/src/session/turn.rs b/codex-rs/core/src/session/turn.rs
index f16b525002fc..89bad5b75769 100644
--- a/codex-rs/core/src/session/turn.rs
+++ b/codex-rs/core/src/session/turn.rs
@@ -1182,8 +1182,8 @@ pub(crate) async fn built_tools(
     let turn_context = step_context.turn.as_ref();
     let mcp_connection_manager = step_context.mcp.manager();
     let has_mcp_servers = mcp_connection_manager.has_servers();
-    let all_mcp_tools = mcp_connection_manager
-        .list_all_tools()
+    let all_mcp_tools = step_context
+        .mcp_tools()
         .or_cancel(cancellation_token)
         .await?;
     let loaded_plugins = sess
@@ -1196,7 +1196,7 @@ pub(crate) async fn built_tools(
 
     let apps_enabled = turn_context.apps_enabled();
     let accessible_connectors =
-        apps_enabled.then(|| connectors::accessible_connectors_from_mcp_tools(&all_mcp_tools));
+        apps_enabled.then(|| connectors::accessible_connectors_from_mcp_tools(all_mcp_tools));
     let accessible_connectors_with_enabled_state =
         accessible_connectors.as_ref().map(|connectors| {
             connectors::with_app_enabled_state(connectors.clone(), &turn_context.config)
@@ -1289,7 +1289,7 @@ pub(crate) async fn built_tools(
             .await
         };
     let mcp_tool_exposure = build_mcp_tool_exposure(
-        &all_mcp_tools,
+        all_mcp_tools,
         connectors.as_deref(),
         &turn_context.config,
         search_tool_enabled(turn_context),
diff --git a/codex-rs/core/src/session/world_state.rs b/codex-rs/core/src/session/world_state.rs
index a0d93cac8317..c7743c3fe18c 100644
--- a/codex-rs/core/src/session/world_state.rs
+++ b/codex-rs/core/src/session/world_state.rs
@@ -41,9 +41,9 @@ impl Session {
         }
         let apps_available =
             if turn_context.config.include_apps_instructions && turn_context.apps_enabled() {
-                let tools = step_context.mcp.manager().list_all_tools().await;
+                let tools = step_context.mcp_tools().await;
                 connectors::with_app_enabled_state(
-                    connectors::accessible_connectors_from_mcp_tools(&tools),
+                    connectors::accessible_connectors_from_mcp_tools(tools),
                     &turn_context.config,
                 )
                 .into_iter()