Enable request_user_input in Default mode (#12735)

## Summary
- allow `request_user_input` in Default collaboration mode as well as
Plan
- update the Default-mode instructions to prefer assumptions first and
use `request_user_input` only when a question is unavoidable
- update request_user_input and app-server tests to match the new
Default-mode behavior
- refactor collaboration-mode availability plumbing into
`CollaborationModesConfig` for future mode-related flags

## Codex author
`codex resume 019c9124-ed28-7c13-96c6-b916b1c97d49`

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

@@ -12,6 +12,7 @@ use codex_core::built_in_model_providers;
 use codex_core::default_client::originator;
 use codex_core::error::CodexErr;
 use codex_core::features::Feature;
+use codex_core::models_manager::collaboration_mode_presets::CollaborationModesConfig;
 use codex_otel::OtelManager;
 use codex_otel::TelemetryAuthMode;
 use codex_protocol::ThreadId;
@@ -584,6 +585,11 @@ async fn prefers_apikey_when_config_prefers_apikey_even_with_chatgpt_tokens() {
         auth_manager,
         SessionSource::Exec,
         config.model_catalog.clone(),
+        CollaborationModesConfig {
+            default_mode_request_user_input: config
+                .features
+                .enabled(Feature::DefaultModeRequestUserInput),
+        },
     );
     let NewThread { thread: codex, .. } = thread_manager
         .start_thread(config)

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

@@ -1,4 +1,5 @@
 use codex_core::CodexAuth;
+use codex_core::models_manager::collaboration_mode_presets::CollaborationModesConfig;
 use codex_core::models_manager::manager::ModelsManager;
 use codex_protocol::openai_models::TruncationPolicyConfig;
 use core_test_support::load_default_config_for_test;
@@ -12,7 +13,12 @@ async fn offline_model_info_without_tool_output_override() {
     let auth_manager = codex_core::test_support::auth_manager_from_auth(
         CodexAuth::create_dummy_chatgpt_auth_for_testing(),
     );
-    let manager = ModelsManager::new(config.codex_home.clone(), auth_manager, None);
+    let manager = ModelsManager::new(
+        config.codex_home.clone(),
+        auth_manager,
+        None,
+        CollaborationModesConfig::default(),
+    );
 
     let model_info = manager.get_model_info("gpt-5.1", &config).await;
 
@@ -30,7 +36,12 @@ async fn offline_model_info_with_tool_output_override() {
     let auth_manager = codex_core::test_support::auth_manager_from_auth(
         CodexAuth::create_dummy_chatgpt_auth_for_testing(),
     );
-    let manager = ModelsManager::new(config.codex_home.clone(), auth_manager, None);
+    let manager = ModelsManager::new(
+        config.codex_home.clone(),
+        auth_manager,
+        None,
+        CollaborationModesConfig::default(),
+    );
 
     let model_info = manager.get_model_info("gpt-5.1-codex", &config).await;
 

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

@@ -86,8 +86,10 @@ async fn request_user_input_round_trip_for_mode(mode: ModeKind) -> anyhow::Resul
         session_configured,
         ..
     } = builder
-        .with_config(|config| {
-            config.features.enable(Feature::CollaborationModes);
+        .with_config(move |config| {
+            if mode == ModeKind::Default {
+                config.features.enable(Feature::DefaultModeRequestUserInput);
+            }
         })
         .build(&server)
         .await?;
@@ -198,18 +200,13 @@ where
 
     let server = start_mock_server().await;
 
-    let builder = test_codex();
+    let mut builder = test_codex();
     let TestCodex {
         codex,
         cwd,
         session_configured,
         ..
-    } = builder
-        .with_config(|config| {
-            config.features.enable(Feature::CollaborationModes);
-        })
-        .build(&server)
-        .await?;
+    } = builder.build(&server).await?;
 
     let mode_slug = mode_name.to_lowercase().replace(' ', "-");
     let call_id = format!("user-input-{mode_slug}-call");
@@ -290,7 +287,7 @@ async fn request_user_input_rejected_in_execute_mode_alias() -> anyhow::Result<(
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn request_user_input_rejected_in_default_mode() -> anyhow::Result<()> {
+async fn request_user_input_rejected_in_default_mode_by_default() -> anyhow::Result<()> {
     assert_request_user_input_rejected("Default", |model| CollaborationMode {
         mode: ModeKind::Default,
         settings: Settings {
@@ -302,6 +299,11 @@ async fn request_user_input_rejected_in_default_mode() -> anyhow::Result<()> {
     .await
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn request_user_input_round_trip_in_default_mode_with_feature() -> anyhow::Result<()> {
+    request_user_input_round_trip_for_mode(ModeKind::Default).await
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn request_user_input_rejected_in_pair_mode_alias() -> anyhow::Result<()> {
     assert_request_user_input_rejected("Pair Programming", |model| CollaborationMode {