diff --git a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
index 9caf631dd..5531a2674 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
@@ -347,7 +347,7 @@ async fn multi_agent_v2_spawn_requires_task_name() {
         Arc::new(turn),
         "spawn_agent",
         function_payload(json!({
-            "message": "inspect this repo"
+            "items": [{"type": "text", "text": "inspect this repo"}]
         })),
     );
     let Err(err) = SpawnAgentHandlerV2.handle(invocation).await else {
@@ -359,6 +359,42 @@ async fn multi_agent_v2_spawn_requires_task_name() {
     assert!(message.contains("missing field `task_name`"));
 }
 
+#[tokio::test]
+async fn multi_agent_v2_spawn_rejects_legacy_message_field() {
+    let (mut session, mut turn) = make_session_and_context().await;
+    let manager = thread_manager();
+    let root = manager
+        .start_thread((*turn.config).clone())
+        .await
+        .expect("root thread should start");
+    session.services.agent_control = manager.agent_control();
+    session.conversation_id = root.thread_id;
+    let mut config = (*turn.config).clone();
+    config
+        .features
+        .enable(Feature::MultiAgentV2)
+        .expect("test config should allow feature update");
+    turn.config = Arc::new(config);
+
+    let invocation = invocation(
+        Arc::new(session),
+        Arc::new(turn),
+        "spawn_agent",
+        function_payload(json!({
+            "message": "inspect this repo",
+            "items": [{"type": "text", "text": "inspect this repo"}],
+            "task_name": "worker"
+        })),
+    );
+    let Err(err) = SpawnAgentHandlerV2.handle(invocation).await else {
+        panic!("legacy message field should be rejected");
+    };
+    let FunctionCallError::RespondToModel(message) = err else {
+        panic!("legacy message field should surface as a model-facing error");
+    };
+    assert!(message.contains("unknown field `message`"));
+}
+
 #[tokio::test]
 async fn spawn_agent_errors_when_manager_dropped() {
     let (session, turn) = make_session_and_context().await;
@@ -408,7 +444,7 @@ async fn multi_agent_v2_spawn_returns_path_and_send_message_accepts_relative_pat
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "test_process"
             })),
         ))
@@ -503,7 +539,7 @@ async fn multi_agent_v2_spawn_rejects_legacy_fork_context() {
             Arc::new(turn),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "worker",
                 "fork_context": true
             })),
@@ -542,7 +578,7 @@ async fn multi_agent_v2_spawn_rejects_invalid_fork_turns_string() {
             Arc::new(turn),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "worker",
                 "fork_turns": "banana"
             })),
@@ -581,7 +617,7 @@ async fn multi_agent_v2_spawn_rejects_zero_fork_turns() {
             Arc::new(turn),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "worker",
                 "fork_turns": "0"
             })),
@@ -695,7 +731,7 @@ async fn multi_agent_v2_list_agents_returns_completed_status_and_last_task_messa
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "worker"
             })),
         ))
@@ -873,7 +909,7 @@ async fn multi_agent_v2_list_agents_omits_closed_agents() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "worker"
             })),
         ))
@@ -937,7 +973,7 @@ async fn multi_agent_v2_send_message_rejects_structured_items() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -995,7 +1031,7 @@ async fn multi_agent_v2_send_message_interrupts_busy_child_without_triggering_tu
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -1132,7 +1168,7 @@ async fn multi_agent_v2_assign_task_interrupts_busy_child_without_losing_message
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -1261,7 +1297,7 @@ async fn multi_agent_v2_assign_task_completion_notifies_parent_on_every_turn() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -1390,7 +1426,7 @@ async fn multi_agent_v2_interrupted_turn_does_not_notify_parent() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -1466,7 +1502,7 @@ async fn multi_agent_v2_spawn_includes_agent_id_key_when_named() {
             Arc::new(turn),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "test_process"
             })),
         ))
@@ -1504,7 +1540,7 @@ async fn multi_agent_v2_spawn_surfaces_task_name_validation_errors() {
         Arc::new(turn),
         "spawn_agent",
         function_payload(json!({
-            "message": "inspect this repo",
+            "items": [{"type": "text", "text": "inspect this repo"}],
             "task_name": "BadName"
         })),
     );
@@ -2131,7 +2167,7 @@ async fn multi_agent_v2_wait_agent_accepts_timeout_only_argument() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -2377,7 +2413,7 @@ async fn multi_agent_v2_wait_agent_returns_summary_for_mailbox_activity() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "test_process"
             })),
         ))
@@ -2468,7 +2504,7 @@ async fn multi_agent_v2_wait_agent_waits_for_new_mail_after_start() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -2568,7 +2604,7 @@ async fn multi_agent_v2_wait_agent_wakes_on_any_mailbox_notification() {
                 turn.clone(),
                 "spawn_agent",
                 function_payload(json!({
-                    "message": format!("boot {task_name}"),
+                    "items": [{"type": "text", "text": format!("boot {task_name}")}],
                     "task_name": task_name
                 })),
             ))
@@ -2655,7 +2691,7 @@ async fn multi_agent_v2_wait_agent_does_not_return_completed_content() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "boot worker",
+                "items": [{"type": "text", "text": "boot worker"}],
                 "task_name": "worker"
             })),
         ))
@@ -2741,7 +2777,7 @@ async fn multi_agent_v2_close_agent_accepts_task_name_target() {
             turn.clone(),
             "spawn_agent",
             function_payload(json!({
-                "message": "inspect this repo",
+                "items": [{"type": "text", "text": "inspect this repo"}],
                 "task_name": "worker"
             })),
         ))
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
index ac0beb675..c710a6e21 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
@@ -40,7 +40,7 @@ impl ToolHandler for Handler {
             .map(str::trim)
             .filter(|role| !role.is_empty());
 
-        let initial_operation = parse_collab_input(args.message, args.items)?;
+        let initial_operation = parse_collab_input(/*message*/ None, Some(args.items))?;
         let prompt = render_input_preview(&initial_operation);
 
         let session_source = turn.session_source.clone();
@@ -200,9 +200,9 @@ impl ToolHandler for Handler {
 }
 
 #[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields)]
 struct SpawnAgentArgs {
-    message: Option<String>,
-    items: Option<Vec<UserInput>>,
+    items: Vec<UserInput>,
     task_name: String,
     agent_type: Option<String>,
     model: Option<String>,
diff --git a/codex-rs/core/src/tools/spec_tests.rs b/codex-rs/core/src/tools/spec_tests.rs
index 728351291..7c5cb8810 100644
--- a/codex-rs/core/src/tools/spec_tests.rs
+++ b/codex-rs/core/src/tools/spec_tests.rs
@@ -497,9 +497,14 @@ fn test_build_specs_multi_agent_v2_uses_task_names_and_hides_resume() {
         panic!("spawn_agent should use object params");
     };
     assert!(properties.contains_key("task_name"));
+    assert!(properties.contains_key("items"));
     assert!(properties.contains_key("fork_turns"));
+    assert!(!properties.contains_key("message"));
     assert!(!properties.contains_key("fork_context"));
-    assert_eq!(required.as_ref(), Some(&vec!["task_name".to_string()]));
+    assert_eq!(
+        required.as_ref(),
+        Some(&vec!["task_name".to_string(), "items".to_string()])
+    );
     let output_schema = output_schema
         .as_ref()
         .expect("spawn_agent should define output schema");
diff --git a/codex-rs/tools/src/agent_tool.rs b/codex-rs/tools/src/agent_tool.rs
index a278440b6..fc87dcc0f 100644
--- a/codex-rs/tools/src/agent_tool.rs
+++ b/codex-rs/tools/src/agent_tool.rs
@@ -66,7 +66,7 @@ pub fn create_spawn_agent_tool_v2(options: SpawnAgentToolOptions<'_>) -> ToolSpe
         defer_loading: None,
         parameters: JsonSchema::Object {
             properties,
-            required: Some(vec!["task_name".to_string()]),
+            required: Some(vec!["task_name".to_string(), "items".to_string()]),
             additional_properties: Some(false.into()),
         },
         output_schema: Some(spawn_agent_output_schema_v2()),
@@ -594,15 +594,6 @@ fn spawn_agent_common_properties_v1(agent_type_description: &str) -> BTreeMap<St
 
 fn spawn_agent_common_properties_v2(agent_type_description: &str) -> BTreeMap<String, JsonSchema> {
     BTreeMap::from([
-        (
-            "message".to_string(),
-            JsonSchema::String {
-                description: Some(
-                    "Initial plain-text task for the new agent. Use either message or items."
-                        .to_string(),
-                ),
-            },
-        ),
         ("items".to_string(), create_collab_input_items_schema()),
         (
             "agent_type".to_string(),
diff --git a/codex-rs/tools/src/agent_tool_tests.rs b/codex-rs/tools/src/agent_tool_tests.rs
index ce312ba36..a794ff380 100644
--- a/codex-rs/tools/src/agent_tool_tests.rs
+++ b/codex-rs/tools/src/agent_tool_tests.rs
@@ -56,7 +56,9 @@ fn spawn_agent_tool_v2_requires_task_name_and_lists_visible_models() {
     assert!(description.contains("visible display (`visible-model`)"));
     assert!(!description.contains("hidden display (`hidden-model`)"));
     assert!(properties.contains_key("task_name"));
+    assert!(properties.contains_key("items"));
     assert!(properties.contains_key("fork_turns"));
+    assert!(!properties.contains_key("message"));
     assert!(!properties.contains_key("fork_context"));
     assert_eq!(
         properties.get("agent_type"),
@@ -64,7 +66,10 @@ fn spawn_agent_tool_v2_requires_task_name_and_lists_visible_models() {
             description: Some("role help".to_string()),
         })
     );
-    assert_eq!(required, Some(vec!["task_name".to_string()]));
+    assert_eq!(
+        required,
+        Some(vec!["task_name".to_string(), "items".to_string()])
+    );
     assert_eq!(
         output_schema.expect("spawn_agent output schema")["required"],
         json!(["agent_id", "task_name", "nickname"])