Use MCP bindings as the step tool catalog (#36360)

## What changed

- Read the frozen MCP tool catalog directly from the step-scoped `McpBinding`
  when building tool routers, plugin injections, and connector state.
- Remove the redundant `Vec<ToolInfo>` from `StepContext` and stop returning a
  duplicate catalog from `built_tools`.

GitOrigin-RevId: d12d694e1224da3f6ccb1960868491f0d80c6e19

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

@@ -3105,7 +3105,7 @@ impl Session {
         }
         .or_cancel(cancellation_token)
         .await?;
-        let (mcp_tools, tool_router) = turn::built_tools(
+        let tool_router = turn::built_tools(
             self.as_ref(),
             turn_context.as_ref(),
             &environments,
@@ -3121,7 +3121,6 @@ impl Session {
             selected_capability_roots,
             executor_capability_discovery,
             mcp,
-            mcp_tools,
             tool_router,
             loaded_agents_md,
         }))

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

@@ -7,7 +7,6 @@ use crate::tools::router::ToolRouter;
 use codex_exec_server::ExecutorCapabilityDiscoverySnapshot;
 use codex_exec_server::ResolvedSelectedCapabilityRoot;
 use codex_mcp::McpBinding;
-use codex_mcp::ToolInfo;
 
 /// Request-scoped state that may change between model sampling requests.
 pub(crate) struct StepContext {
@@ -19,8 +18,6 @@ pub(crate) struct StepContext {
     pub(crate) executor_capability_discovery: Option<Arc<ExecutorCapabilityDiscoverySnapshot>>,
     /// The exact MCP connections, configuration, and catalog captured for this step.
     pub(crate) mcp: Arc<McpBinding>,
-    /// The fixed MCP tool list used for this exact sampling request.
-    pub(crate) mcp_tools: Vec<ToolInfo>,
     /// The finalized tool plan advertised and executed for this exact sampling request.
     pub(crate) tool_router: Arc<ToolRouter>,
     /// The canonical AGENTS.md value observed with this environment snapshot.

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

@@ -217,7 +217,6 @@ impl StepContext {
             mcp: Arc::new(codex_mcp::McpBinding::empty(mcp_config_for_test(
                 &turn.config,
             ))),
-            mcp_tools: Vec::new(),
             tool_router: Arc::new(ToolRouter::from_parts(
                 ToolRegistry::empty_for_test(),
                 Vec::new(),

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

@@ -80,7 +80,6 @@ use codex_features::Feature;
 use codex_file_system::FindUpErrorPolicy;
 use codex_file_system::find_nearest_ancestor_with_markers;
 use codex_login::CodexAuth;
-use codex_mcp::ToolInfo;
 use codex_protocol::ResponseItemId;
 use codex_protocol::config_types::AutoCompactTokenLimitScope;
 use codex_protocol::config_types::ModeKind;
@@ -742,9 +741,9 @@ async fn build_skills_and_plugins(
         // Plugin mentions need raw MCP/app inventory even when app tools
         // are normally hidden so we can describe the plugin's currently
         // usable capabilities for this turn.
-        step_context.mcp.tools().to_vec()
+        step_context.mcp.tools()
     } else {
-        Vec::new()
+        &[]
     };
     let available_connectors = if turn_context.apps_enabled() {
         let connectors = codex_connectors::merge::merge_plugin_connectors_with_accessible(
@@ -752,7 +751,7 @@ async fn build_skills_and_plugins(
                 .connector_ids()
                 .iter()
                 .map(|connector_id| connector_id.0.clone()),
-            connectors::accessible_connectors_from_mcp_tools(&mcp_tools),
+            connectors::accessible_connectors_from_mcp_tools(mcp_tools),
         );
         connectors::with_app_enabled_state(connectors, &turn_context.config)
     } else {
@@ -809,8 +808,7 @@ async fn build_skills_and_plugins(
         &available_connectors,
         &skill_name_counts_lower,
     );
-    let plugin_items =
-        build_plugin_injections(mentioned_plugins, &mcp_tools, &available_connectors);
+    let plugin_items = build_plugin_injections(mentioned_plugins, mcp_tools, &available_connectors);
     let mut explicitly_enabled_connectors = collect_explicit_app_ids(user_input);
     explicitly_enabled_connectors.extend(skill_connector_ids);
     let connector_names_by_id = available_connectors
@@ -1469,13 +1467,13 @@ pub(crate) async fn built_tools(
     mcp: &codex_mcp::McpBinding,
     step_store: &ExtensionData,
     prepared_recommendations: PreparedToolRecommendations,
-) -> (Vec<ToolInfo>, Arc<ToolRouter>) {
-    let all_mcp_tools = mcp.tools().to_vec();
+) -> Arc<ToolRouter> {
+    let all_mcp_tools = mcp.tools();
     let connector_snapshot = mcp.config().connector_snapshot.clone();
 
     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)
@@ -1551,7 +1549,7 @@ pub(crate) async fn built_tools(
             .instrument(trace_span!("built_tools.load_discoverable_tools"))
             .await
         };
-    let tool_router = Arc::new(build_tool_router(
+    Arc::new(build_tool_router(
         sess,
         turn_context,
         environments,
@@ -1559,8 +1557,7 @@ pub(crate) async fn built_tools(
         connectors.as_deref(),
         step_store,
         tool_suggest_candidates.as_ref(),
-    ));
-    (all_mcp_tools, tool_router)
+    ))
 }
 
 #[derive(Debug)]

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

@@ -168,7 +168,7 @@ impl Session {
         let apps_available =
             if turn_context.config.include_apps_instructions && turn_context.apps_enabled() {
                 connectors::with_app_enabled_state(
-                    connectors::accessible_connectors_from_mcp_tools(&step_context.mcp_tools),
+                    connectors::accessible_connectors_from_mcp_tools(step_context.mcp.tools()),
                     &turn_context.config,
                 )
                 .into_iter()