Allow turns when the agent message board is unavailable (#53369)

## Why

With `multi_agent_v2.disable_direct_message` enabled, an unavailable agent message board could cause tool router construction to reject the turn.

## What changed

Remove the requirement that the router expose the board's `post` tool. Unavailable board calls return an unsupported-call error to the model, allowing the turn to continue.

## Testing

Update scenario coverage for a disabled board feature, legacy agents, and ephemeral sessions. Assert that unavailable board calls return an error to the model, that `post`, `send_message`, and `followup_task` are not advertised, and that no board database is created.

GitOrigin-RevId: cb9571459c128d84c3c96f185e70c404e0463473

codex-rs/core/src/tools/spec_plan.rs

@@ -542,33 +542,14 @@ pub(crate) fn finalize_tool_router(
         .filter(|info| !info.is_empty());
     let child_management_tools = required_child_management_tool_names(turn_context, model_info);
 
-    let router = ToolRouter::from_parts(
+    Ok(ToolRouter::from_parts(
         registry,
         model_visible_specs,
         tool_mode,
         code_mode_tool_names,
         tool_namespaces_info,
         &child_management_tools,
-    );
-    // Internal workers can inherit MAv2 configuration without using the board.
-    if multi_agent_v2_enabled(turn_context)
-        && collab_tools_enabled(turn_context, model_info)
-        && turn_context.config.multi_agent_v2.disable_direct_message
-        && !turn_context.session_source.is_internal()
-    {
-        let post_tool = ToolName::new(
-            turn_context.config.multi_agent_v2.tool_namespace.clone(),
-            "post",
-        );
-        if !router.exposes_tool(&post_tool) {
-            return Err(CodexErrorDetails::InvalidRequest(
-                "disable_direct_message requires an available agent message board in this session"
-                    .to_owned(),
-            )
-            .into());
-        }
-    }
-    Ok(router)
+    ))
 }
 
 fn apply_direct_model_only_namespace_overrides(

codex-rs/core/tests/suite/scenarios_agent_message_board.rs

@@ -89,16 +89,28 @@ fn configure(config: &mut codex_core::config::Config) {
 #[test_case::test_case(true, false, false; "legacy_agents")]
 #[test_case::test_case(true, true, true; "ephemeral")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn board_requires_persistent_v2_runtime(
+async fn unavailable_board_calls_return_model_errors(
     board_enabled: bool,
     multi_agent_v2: bool,
     ephemeral: bool,
 ) -> anyhow::Result<()> {
     let server = responses::start_mock_server().await;
-    let mock = responses::mount_sse_once(&server, done()).await;
+    let mock = responses::mount_sse_sequence(
+        &server,
+        vec![
+            tool(
+                "missing-board",
+                "post",
+                json!({"new_channel_name":"design", "text":"A decision."}),
+            ),
+            done(),
+        ],
+    )
+    .await;
     let test = test_codex()
         .with_config(move |config| {
             configure(config);
+            config.multi_agent_v2.disable_direct_message = true;
             if !board_enabled {
                 config
                     .features
@@ -115,15 +127,22 @@ async fn board_requires_persistent_v2_runtime(
         })
         .build_with_auto_env(&server)
         .await?;
-    test.submit_turn("Hello.").await?;
-    assert!(
-        responses::namespace_child_tool(
-            &mock.single_request().body_json(),
-            "collaboration",
-            "post"
-        )
-        .is_none()
+    test.submit_turn("Try posting the decision on the board.")
+        .await?;
+    let requests = mock.requests();
+    assert_eq!(requests.len(), 2);
+    assert_eq!(
+        requests[1]
+            .function_call_output_text("missing-board")
+            .as_deref(),
+        Some("unsupported call: collaborationpost")
     );
+    for name in ["post", "send_message", "followup_task"] {
+        assert!(
+            responses::namespace_child_tool(&requests[0].body_json(), "collaboration", name)
+                .is_none()
+        );
+    }
     assert!(
         !test
             .config