diff --git a/codex-rs/core/src/tools/spec_plan.rs b/codex-rs/core/src/tools/spec_plan.rs
index 928a37bad1..32d5d6b786 100644
--- a/codex-rs/core/src/tools/spec_plan.rs
+++ b/codex-rs/core/src/tools/spec_plan.rs
@@ -90,6 +90,7 @@ use codex_tools::shell_command_backend_for_features;
 use codex_tools::shell_type_for_model_and_features;
 use futures::future::BoxFuture;
 use std::collections::BTreeMap;
+use std::collections::btree_map::Entry;
 use std::sync::Arc;
 use tracing::instrument;
 
@@ -261,9 +262,10 @@ pub(crate) fn finalize_tool_router(
         append_tool_search_executor(turn_context, &mut registry, tool_search_handler_cache);
     }
 
-    register_code_mode_executors(turn_context, &mut registry);
+    let code_mode_tool_names = register_code_mode_executors(turn_context, &mut registry);
 
-    let model_visible_specs = build_model_visible_specs(turn_context, &registry, hosted_specs);
+    let model_visible_specs =
+        build_model_visible_specs(turn_context, &registry, &code_mode_tool_names, hosted_specs);
     ToolRouter::from_parts(registry, model_visible_specs)
 }
 
@@ -293,6 +295,7 @@ fn apply_direct_model_only_namespace_overrides(
 fn build_model_visible_specs(
     turn_context: &TurnContext,
     registry: &ToolRegistry,
+    code_mode_tool_names: &BTreeMap<String, ToolName>,
     hosted_specs: Vec<ToolSpec>,
 ) -> Vec<ToolSpec> {
     let mut specs = Vec::new();
@@ -306,6 +309,7 @@ fn build_model_visible_specs(
                 turn_context,
                 exposure,
                 &tool_name,
+                code_mode_tool_names,
                 spec,
             ));
         }
@@ -324,6 +328,7 @@ fn spec_for_model_request(
     turn_context: &TurnContext,
     exposure: ToolExposure,
     tool_name: &ToolName,
+    code_mode_tool_names: &BTreeMap<String, ToolName>,
     spec: ToolSpec,
 ) -> ToolSpec {
     let tool_mode = effective_tool_mode(turn_context);
@@ -331,6 +336,11 @@ fn spec_for_model_request(
         && exposure.is_available_in_code_mode()
         && !is_excluded_from_code_mode(turn_context, tool_name)
         && codex_code_mode::is_code_mode_nested_tool(spec.name())
+        && code_mode_tool_names
+            .get(&codex_code_mode::normalize_code_mode_identifier(
+                &codex_tools::code_mode_name_for_tool_name(tool_name),
+            ))
+            .is_some_and(|winner| winner == tool_name)
     {
         codex_tools::augment_tool_spec_for_code_mode(spec)
     } else {
@@ -495,12 +505,16 @@ fn is_excluded_from_code_mode(turn_context: &TurnContext, tool_name: &ToolName)
     })
 }
 
-fn register_code_mode_executors(turn_context: &TurnContext, registry: &mut ToolRegistry) {
+fn register_code_mode_executors(
+    turn_context: &TurnContext,
+    registry: &mut ToolRegistry,
+) -> BTreeMap<String, ToolName> {
     let tool_mode = effective_tool_mode(turn_context);
     if !matches!(tool_mode, ToolMode::CodeMode | ToolMode::CodeModeOnly) {
-        return;
+        return BTreeMap::new();
     }
 
+    let mut code_mode_tool_names = BTreeMap::new();
     let mut code_mode_nested_tool_specs = Vec::new();
     let mut exec_prompt_tool_specs = Vec::new();
     let mut deferred_exec_prompt_tool_specs = Vec::new();
@@ -511,11 +525,33 @@ fn register_code_mode_executors(turn_context: &TurnContext, registry: &mut ToolR
             continue;
         }
 
-        if is_excluded_from_code_mode(turn_context, &executor.tool_name()) {
+        let tool_name = executor.tool_name();
+        if is_excluded_from_code_mode(turn_context, &tool_name) {
             continue;
         }
 
         let spec = executor.spec();
+        let Some(code_mode_tool) = codex_tools::tool_spec_to_code_mode_tool_definition(&spec)
+        else {
+            continue;
+        };
+
+        let code_mode_name = code_mode_tool.name;
+        match code_mode_tool_names.entry(codex_code_mode::normalize_code_mode_identifier(
+            &code_mode_name,
+        )) {
+            Entry::Vacant(entry) => {
+                entry.insert(tool_name);
+            }
+            Entry::Occupied(_) => {
+                tracing::warn!(
+                    tool_name = %tool_name,
+                    code_mode_name = %code_mode_name,
+                    "skipping tool with a duplicate normalized code-mode name"
+                );
+                continue;
+            }
+        }
 
         if exposure == ToolExposure::Deferred {
             if deferred_tools_guidance_enabled {
@@ -528,19 +564,9 @@ fn register_code_mode_executors(turn_context: &TurnContext, registry: &mut ToolR
     }
 
     if turn_context.model_info.use_responses_lite {
-        let code_mode_tool_names =
-            collect_code_mode_exec_prompt_tool_definitions(code_mode_nested_tool_specs.iter())
-                .into_iter()
-                .map(|tool| {
-                    (
-                        codex_code_mode::normalize_code_mode_identifier(&tool.name),
-                        tool.tool_name,
-                    )
-                })
-                .collect();
         turn_context
             .turn_metadata_state
-            .set_code_mode_tool_names(code_mode_tool_names);
+            .set_code_mode_tool_names(code_mode_tool_names.clone());
     }
 
     let namespace_descriptions = code_mode_namespace_descriptions(&exec_prompt_tool_specs);
@@ -567,6 +593,8 @@ fn register_code_mode_executors(turn_context: &TurnContext, registry: &mut ToolR
 
     registry.prepend_trusted(Arc::new(CodeModeWaitHandler));
     registry.prepend_trusted(Arc::new(execute_handler));
+
+    code_mode_tool_names
 }
 
 #[instrument(level = "trace", skip_all, fields(tool_spec_count = specs.len()))]
diff --git a/codex-rs/core/src/tools/spec_plan_tests.rs b/codex-rs/core/src/tools/spec_plan_tests.rs
index cf958e5f56..8410a1add3 100644
--- a/codex-rs/core/src/tools/spec_plan_tests.rs
+++ b/codex-rs/core/src/tools/spec_plan_tests.rs
@@ -31,6 +31,7 @@ use serde_json::json;
 use crate::WaitForEnvironmentToolConfig;
 use crate::config::CurrentTimeReminderConfig;
 use crate::environment_selection::TurnEnvironmentState;
+use crate::responses_metadata::CodexResponsesRequestKind;
 use crate::session::step_context::StepContext;
 use crate::session::tests::make_session_and_context;
 use crate::session::tests::mcp_config_for_test;
@@ -1079,6 +1080,93 @@ async fn unified_tool_runtimes_preserve_source_order_and_collision_priority() {
     assert_eq!(tool.description, "lookup test tool");
 }
 
+#[tokio::test]
+async fn code_mode_uses_the_first_normalized_tool_identity() {
+    for (code_mode_only, winner_exposure, shadow_is_deferred) in [
+        (false, ToolExposure::Direct, true),
+        (false, ToolExposure::Deferred, false),
+        (true, ToolExposure::Direct, true),
+        (true, ToolExposure::Deferred, false),
+    ] {
+        let mut metadata_state = None;
+        let plan = probe_with(
+            |turn| {
+                set_feature(turn, Feature::CodeMode, /*enabled*/ true);
+                if code_mode_only {
+                    set_feature(turn, Feature::CodeModeOnly, /*enabled*/ true);
+                }
+                turn.model_info.supports_search_tool = true;
+                turn.model_info.use_responses_lite = true;
+                metadata_state = Some(Arc::clone(&turn.turn_metadata_state));
+            },
+            ToolPlanInputs {
+                tool_runtimes: vec![mcp_runtime(
+                    "winner",
+                    "normalized-alias",
+                    "lookup",
+                    winner_exposure,
+                )],
+                dynamic_tools: vec![dynamic_tool(
+                    Some("normalized_alias"),
+                    "lookup",
+                    shadow_is_deferred,
+                )],
+                ..ToolPlanInputs::default()
+            },
+        )
+        .await;
+
+        let winner_name = ToolName::namespaced("normalized-alias", "lookup");
+        let shadow_name = ToolName::namespaced("normalized_alias", "lookup");
+        plan.assert_registered_contains(&[&winner_name.to_string(), &shadow_name.to_string()]);
+        assert_eq!(plan.exposure(&winner_name.to_string()), winner_exposure);
+        assert_eq!(
+            plan.exposure(&shadow_name.to_string()),
+            if shadow_is_deferred {
+                ToolExposure::Deferred
+            } else {
+                ToolExposure::Direct
+            },
+        );
+
+        let metadata = metadata_state
+            .expect("tool planning should capture the turn metadata")
+            .to_responses_metadata(
+                "installation".to_string(),
+                "window".to_string(),
+                CodexResponsesRequestKind::Turn,
+            );
+        let code_mode_tool_names = metadata
+            .code_mode_tool_names
+            .as_ref()
+            .expect("Responses Lite should receive the supported code-mode tools");
+        assert_eq!(
+            code_mode_tool_names.get("normalized_alias__lookup"),
+            Some(&winner_name),
+        );
+        assert!(!code_mode_tool_names.contains_key(codex_tools::TOOL_SEARCH_TOOL_NAME));
+
+        if !code_mode_only && !shadow_is_deferred {
+            let ToolSpec::Namespace(namespace) = plan.visible_spec("normalized_alias") else {
+                panic!("expected the shadowed dynamic tool to remain directly visible");
+            };
+            let [ResponsesApiNamespaceTool::Function(shadow)] = namespace.tools.as_slice() else {
+                panic!("expected exactly one shadowed dynamic tool");
+            };
+            assert_eq!(shadow.description, "lookup dynamic tool");
+        }
+
+        let ToolSpec::Freeform(exec) = plan.visible_spec(codex_code_mode::PUBLIC_TOOL_NAME) else {
+            panic!("expected code mode exec tool");
+        };
+        assert!(!exec.description.contains("lookup dynamic tool"));
+        assert_eq!(
+            exec.description.contains("lookup test tool"),
+            code_mode_only && winner_exposure == ToolExposure::Direct,
+        );
+    }
+}
+
 #[tokio::test]
 async fn deferred_extension_tools_are_discoverable_with_tool_search() {
     let plan = probe_with(
diff --git a/codex-rs/core/tests/suite/code_mode.rs b/codex-rs/core/tests/suite/code_mode.rs
index 2a9bf2b486..d34085cc2e 100644
--- a/codex-rs/core/tests/suite/code_mode.rs
+++ b/codex-rs/core/tests/suite/code_mode.rs
@@ -21,6 +21,7 @@ use codex_protocol::dynamic_tools::DynamicToolNamespaceTool;
 use codex_protocol::dynamic_tools::DynamicToolResponse;
 use codex_protocol::dynamic_tools::DynamicToolSpec;
 use codex_protocol::models::PermissionProfile;
+use codex_protocol::openai_models::ToolMode;
 use codex_protocol::protocol::AskForApproval;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::Op;
@@ -3704,6 +3705,238 @@ text(JSON.stringify(tool));
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn code_mode_uses_the_first_dynamic_tool_for_a_normalized_name() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    for use_responses_lite in [false, true] {
+        let server = responses::start_mock_server().await;
+        let mut builder = test_codex()
+            .with_model_info_override("gpt-5.5", move |model_info| {
+                model_info.use_responses_lite = use_responses_lite;
+                model_info.tool_mode = Some(ToolMode::CodeMode);
+            })
+            .with_config(|config| {
+                config
+                    .features
+                    .enable(Feature::CodeMode)
+                    .expect("code mode should be enabled");
+            });
+        let base_test = builder.build_with_auto_env(&server).await?;
+        let new_thread = base_test
+            .thread_manager
+            .start_thread(StartThreadOptions {
+                dynamic_tools: [
+                    ("foo-bar", "First normalized dynamic tool."),
+                    ("foo_bar", "Shadowed normalized dynamic tool."),
+                ]
+                .into_iter()
+                .map(|(name, description)| {
+                    DynamicToolSpec::Function(DynamicToolFunctionSpec {
+                        name: name.to_string(),
+                        description: description.to_string(),
+                        input_schema: serde_json::json!({
+                            "type": "object",
+                            "properties": {},
+                            "additionalProperties": false,
+                        }),
+                        defer_loading: false,
+                    })
+                })
+                .collect(),
+                ..StartThreadOptions::new(base_test.config.clone())
+            })
+            .await?;
+        let mut test = base_test;
+        test.codex = new_thread.thread;
+        test.session_configured = new_thread.session_configured;
+
+        let first_mock = responses::mount_sse_once(
+            &server,
+            sse(vec![
+                ev_response_created("resp-1"),
+                ev_custom_tool_call(
+                    "call-1",
+                    "exec",
+                    r#"
+const matches = ALL_TOOLS.filter(({ name }) => name === "foo_bar");
+const output = await tools.foo_bar({});
+text(JSON.stringify({
+  count: matches.length,
+  name: matches[0]?.name ?? null,
+  description: matches[0]?.description ?? null,
+  output,
+}));
+"#,
+                ),
+                ev_completed("resp-1"),
+            ]),
+        )
+        .await;
+        let second_mock = responses::mount_sse_once(
+            &server,
+            sse(vec![
+                ev_assistant_message("msg-1", "done"),
+                ev_completed("resp-2"),
+            ]),
+        )
+        .await;
+
+        let cwd = test.config.cwd.clone();
+        let (sandbox_policy, permission_profile) =
+            turn_permission_fields(PermissionProfile::Disabled, cwd.as_path());
+        test.codex
+            .submit(Op::UserInput {
+                items: vec![UserInput::Text {
+                    text: "inspect and call normalized dynamic tools".to_string(),
+                    text_elements: Vec::new(),
+                }],
+                final_output_json_schema: None,
+                responsesapi_client_metadata: None,
+                additional_context: Default::default(),
+                thread_settings: codex_protocol::protocol::ThreadSettingsOverrides {
+                    environments: Some(codex_protocol::protocol::TurnEnvironmentSelections::new(
+                        cwd,
+                        Vec::new(),
+                    )),
+                    approval_policy: Some(AskForApproval::Never),
+                    sandbox_policy: Some(sandbox_policy),
+                    permission_profile,
+                    collaboration_mode: Some(codex_protocol::config_types::CollaborationMode {
+                        mode: codex_protocol::config_types::ModeKind::Default,
+                        settings: codex_protocol::config_types::Settings {
+                            model: test.session_configured.model.clone(),
+                            reasoning_effort: None,
+                            developer_instructions: None,
+                        },
+                    }),
+                    ..Default::default()
+                },
+            })
+            .await?;
+
+        let turn_id = wait_for_event_match(&test.codex, |event| match event {
+            EventMsg::TurnStarted(event) => Some(event.turn_id.clone()),
+            _ => None,
+        })
+        .await;
+        let request = wait_for_event_match(&test.codex, |event| match event {
+            EventMsg::DynamicToolCallRequest(request) => Some(request.clone()),
+            _ => None,
+        })
+        .await;
+        assert_eq!(request.namespace, None);
+        assert_eq!(request.tool, "foo-bar");
+        assert_eq!(request.arguments, serde_json::json!({}));
+        test.codex
+            .submit(Op::DynamicToolResponse {
+                id: request.call_id,
+                response: DynamicToolResponse {
+                    content_items: vec![DynamicToolCallOutputContentItem::InputText {
+                        text: "first-winner".to_string(),
+                    }],
+                    success: true,
+                },
+            })
+            .await?;
+        wait_for_event(&test.codex, |event| match event {
+            EventMsg::TurnComplete(event) => event.turn_id == turn_id,
+            _ => false,
+        })
+        .await;
+
+        let first_body = first_mock.single_request().body_json();
+        let model_tools = if use_responses_lite {
+            first_body["input"]
+                .as_array()
+                .and_then(|input| {
+                    input.iter().find(|item| {
+                        item.get("type").and_then(Value::as_str) == Some("additional_tools")
+                    })
+                })
+                .and_then(|item| item["tools"].as_array())
+                .expect("the Responses Lite request should contain its additional tools")
+        } else {
+            first_body["tools"]
+                .as_array()
+                .expect("the Responses request should contain its visible tools")
+        };
+        let visible_dynamic_tools = model_tools
+            .iter()
+            .filter(|tool| matches!(tool["name"].as_str(), Some("foo-bar" | "foo_bar")))
+            .map(|tool| {
+                (
+                    tool["name"]
+                        .as_str()
+                        .expect("dynamic tools should have a name"),
+                    tool["description"]
+                        .as_str()
+                        .expect("dynamic tools should have a description"),
+                )
+            })
+            .collect::<Vec<_>>();
+        assert_eq!(
+            visible_dynamic_tools,
+            [
+                (
+                    "foo-bar",
+                    concat!(
+                        "First normalized dynamic tool.\n\n",
+                        "exec tool declaration:\n",
+                        "```ts\n",
+                        "declare const tools: { foo_bar(args: {}): Promise<unknown>; };\n",
+                        "```",
+                    ),
+                ),
+                ("foo_bar", "Shadowed normalized dynamic tool."),
+            ]
+        );
+
+        if use_responses_lite {
+            let metadata: Value = serde_json::from_str(
+                first_body["client_metadata"]["x-codex-turn-metadata"]
+                    .as_str()
+                    .expect("Responses Lite should contain serialized turn metadata"),
+            )?;
+            assert_eq!(
+                metadata["code_mode_tool_names"]["foo_bar"],
+                serde_json::json!({
+                    "name": "foo-bar",
+                    "namespace": null,
+                }),
+            );
+            assert!(
+                metadata["code_mode_tool_names"]
+                    .get("tool_search")
+                    .is_none()
+            );
+        }
+
+        let exec_description = model_tools
+            .iter()
+            .find(|tool| tool["name"] == "exec")
+            .and_then(|tool| tool["description"].as_str())
+            .expect("the model request should contain the code-mode exec tool");
+        assert!(!exec_description.contains("First normalized dynamic tool."));
+        assert!(!exec_description.contains("Shadowed normalized dynamic tool."));
+
+        let request = second_mock.single_request();
+        let output = custom_tool_output_last_non_empty_text(&request, "call-1")
+            .expect("code mode should return normalized tool metadata");
+        let result: Value = serde_json::from_str(&output)?;
+        assert_eq!(result["count"], serde_json::json!(1));
+        assert_eq!(result["name"], serde_json::json!("foo_bar"));
+        assert_eq!(result["output"], serde_json::json!("first-winner"));
+        let description = result["description"]
+            .as_str()
+            .expect("the winning tool should have a description");
+        assert!(description.contains("First normalized dynamic tool."));
+        assert!(!description.contains("Shadowed normalized dynamic tool."));
+    }
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn code_mode_can_call_hidden_dynamic_tools() -> Result<()> {
     skip_if_no_network!(Ok(()));