diff --git a/codex-rs/app-server/src/request_processors/external_agent_config_processor.rs b/codex-rs/app-server/src/request_processors/external_agent_config_processor.rs
index b2899f6ba7..8490990af6 100644
--- a/codex-rs/app-server/src/request_processors/external_agent_config_processor.rs
+++ b/codex-rs/app-server/src/request_processors/external_agent_config_processor.rs
@@ -308,7 +308,8 @@ impl ExternalAgentConfigRequestProcessor {
                 initial_history: InitialHistory::Forked(rollout_items),
                 session_source: None,
                 thread_source: None,
-                code_mode_session_provider_selection: Default::default(),
+                code_mode_session_provider_selection:
+                    codex_code_mode::SessionProviderSelection::InProcess,
                 dynamic_tools: Vec::new(),
                 persist_extended_history: false,
                 metrics_service_name: None,
diff --git a/codex-rs/app-server/src/request_processors/thread_processor.rs b/codex-rs/app-server/src/request_processors/thread_processor.rs
index 6cd4ac2996..24e672e55f 100644
--- a/codex-rs/app-server/src/request_processors/thread_processor.rs
+++ b/codex-rs/app-server/src/request_processors/thread_processor.rs
@@ -1105,7 +1105,8 @@ impl ThreadRequestProcessor {
                 },
                 session_source: None,
                 thread_source,
-                code_mode_session_provider_selection: Default::default(),
+                code_mode_session_provider_selection:
+                    codex_code_mode::SessionProviderSelection::InProcess,
                 dynamic_tools: core_dynamic_tools,
                 persist_extended_history: false,
                 metrics_service_name: service_name,
diff --git a/codex-rs/code-mode/src/service.rs b/codex-rs/code-mode/src/service.rs
index cb881ae894..74a62474f4 100644
--- a/codex-rs/code-mode/src/service.rs
+++ b/codex-rs/code-mode/src/service.rs
@@ -157,9 +157,8 @@ pub trait CodeModeSessionProvider: Send + Sync {
 }
 
 /// Selects how a code-mode session is provisioned for a Codex session.
-#[derive(Clone, Default)]
+#[derive(Clone)]
 pub enum SessionProviderSelection {
-    #[default]
     InProcess,
     Disabled,
     Custom(Arc<dyn CodeModeSessionProvider>),
@@ -970,11 +969,11 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn provider_selection_defaults_to_in_process_and_can_disable() {
+    async fn provider_selection_can_use_in_process_or_disable() {
         let delegate = Arc::new(NoopCodeModeSessionDelegate);
 
         assert!(
-            SessionProviderSelection::default()
+            SessionProviderSelection::InProcess
                 .create_session(delegate.clone())
                 .await
                 .unwrap()
diff --git a/codex-rs/core/src/thread_manager.rs b/codex-rs/core/src/thread_manager.rs
index 8d9f4c52ef..321e5195c2 100644
--- a/codex-rs/core/src/thread_manager.rs
+++ b/codex-rs/core/src/thread_manager.rs
@@ -577,7 +577,8 @@ impl ThreadManager {
             initial_history: InitialHistory::New,
             session_source: None,
             thread_source: None,
-            code_mode_session_provider_selection: Default::default(),
+            code_mode_session_provider_selection:
+                codex_code_mode::SessionProviderSelection::InProcess,
             dynamic_tools,
             persist_extended_history,
             metrics_service_name: None,
@@ -948,7 +949,9 @@ impl ThreadManager {
     }
 
     pub(crate) fn agent_control(&self) -> AgentControl {
-        self.agent_control_with_code_mode_session_provider_selection(Default::default())
+        self.agent_control_with_code_mode_session_provider_selection(
+            codex_code_mode::SessionProviderSelection::InProcess,
+        )
     }
 
     fn agent_control_with_code_mode_session_provider_selection(
diff --git a/codex-rs/core/src/thread_manager_tests.rs b/codex-rs/core/src/thread_manager_tests.rs
index 7d0f4a09df..c9b1e60502 100644
--- a/codex-rs/core/src/thread_manager_tests.rs
+++ b/codex-rs/core/src/thread_manager_tests.rs
@@ -348,7 +348,8 @@ async fn start_thread_rejects_explicit_local_environment_when_default_provider_i
             initial_history: InitialHistory::New,
             session_source: None,
             thread_source: None,
-            code_mode_session_provider_selection: Default::default(),
+            code_mode_session_provider_selection:
+                codex_code_mode::SessionProviderSelection::InProcess,
             dynamic_tools: Vec::new(),
             persist_extended_history: false,
             metrics_service_name: None,
@@ -532,7 +533,8 @@ async fn start_thread_keeps_internal_threads_hidden_from_normal_lookups() {
                 InternalSessionSource::MemoryConsolidation,
             )),
             thread_source: None,
-            code_mode_session_provider_selection: Default::default(),
+            code_mode_session_provider_selection:
+                codex_code_mode::SessionProviderSelection::InProcess,
             dynamic_tools: Vec::new(),
             persist_extended_history: false,
             metrics_service_name: None,
diff --git a/codex-rs/core/tests/suite/subagent_notifications.rs b/codex-rs/core/tests/suite/subagent_notifications.rs
index 3c387767df..887567ab09 100644
--- a/codex-rs/core/tests/suite/subagent_notifications.rs
+++ b/codex-rs/core/tests/suite/subagent_notifications.rs
@@ -751,7 +751,8 @@ async fn subagent_stop_replaces_stop_and_skips_internal_subagents() -> Result<()
             initial_history: InitialHistory::New,
             session_source: Some(SessionSource::SubAgent(SubAgentSource::Review)),
             thread_source: None,
-            code_mode_session_provider_selection: Default::default(),
+            code_mode_session_provider_selection:
+                codex_code_mode::SessionProviderSelection::InProcess,
             dynamic_tools: Vec::new(),
             persist_extended_history: false,
             metrics_service_name: None,
diff --git a/codex-rs/memories/write/src/runtime.rs b/codex-rs/memories/write/src/runtime.rs
index dbfac7d8a4..1dc2ff9c0d 100644
--- a/codex-rs/memories/write/src/runtime.rs
+++ b/codex-rs/memories/write/src/runtime.rs
@@ -247,7 +247,8 @@ impl MemoryStartupContext {
                     InternalSessionSource::MemoryConsolidation,
                 )),
                 thread_source: Some(ThreadSource::MemoryConsolidation),
-                code_mode_session_provider_selection: Default::default(),
+                code_mode_session_provider_selection:
+                    codex_code_mode::SessionProviderSelection::InProcess,
                 dynamic_tools: Vec::new(),
                 persist_extended_history: false,
                 metrics_service_name: None,