diff --git a/codex-rs/app-server/src/in_process.rs b/codex-rs/app-server/src/in_process.rs
index 09d57a60a3..09d5bb8bf4 100644
--- a/codex-rs/app-server/src/in_process.rs
+++ b/codex-rs/app-server/src/in_process.rs
@@ -82,6 +82,7 @@ use codex_config::CloudRequirementsLoader;
 use codex_config::LoaderOverrides;
 use codex_config::ThreadConfigLoader;
 use codex_core::config::Config;
+use codex_core::resolve_installation_id;
 use codex_exec_server::EnvironmentManager;
 use codex_feedback::CodexFeedback;
 use codex_login::AuthManager;
@@ -344,7 +345,7 @@ impl InProcessClientHandle {
 /// the runtime is shut down and an `InvalidData` error is returned.
 pub async fn start(args: InProcessStartArgs) -> IoResult<InProcessClientHandle> {
     let initialize = args.initialize.clone();
-    let client = start_uninitialized(args);
+    let client = start_uninitialized(args).await?;
 
     let initialize_response = client
         .request(ClientRequest::Initialize {
@@ -364,10 +365,11 @@ pub async fn start(args: InProcessStartArgs) -> IoResult<InProcessClientHandle>
     Ok(client)
 }
 
-fn start_uninitialized(args: InProcessStartArgs) -> InProcessClientHandle {
+async fn start_uninitialized(args: InProcessStartArgs) -> IoResult<InProcessClientHandle> {
     let channel_capacity = args.channel_capacity.max(1);
     let (client_tx, mut client_rx) = mpsc::channel::<InProcessClientMessage>(channel_capacity);
     let (event_tx, event_rx) = mpsc::channel::<InProcessServerEvent>(channel_capacity);
+    let installation_id = resolve_installation_id(&args.config.codex_home).await?;
 
     let runtime_handle = tokio::spawn(async move {
         let (outgoing_tx, mut outgoing_rx) = mpsc::channel::<OutgoingEnvelope>(channel_capacity);
@@ -427,6 +429,7 @@ fn start_uninitialized(args: InProcessStartArgs) -> InProcessClientHandle {
                 config_warnings: args.config_warnings,
                 session_source: args.session_source,
                 auth_manager,
+                installation_id,
                 rpc_transport: AppServerRpcTransport::InProcess,
                 remote_control_handle: None,
                 plugin_startup_tasks: crate::PluginStartupTasks::Start,
@@ -719,13 +722,13 @@ fn start_uninitialized(args: InProcessStartArgs) -> InProcessClientHandle {
         }
     });
 
-    InProcessClientHandle {
+    Ok(InProcessClientHandle {
         client: InProcessClientSender { client_tx },
         event_rx,
         runtime_handle,
         #[cfg(test)]
         _test_codex_home: None,
-    }
+    })
 }
 
 #[cfg(test)]
diff --git a/codex-rs/app-server/src/lib.rs b/codex-rs/app-server/src/lib.rs
index 4b1723d88c..838287a7d8 100644
--- a/codex-rs/app-server/src/lib.rs
+++ b/codex-rs/app-server/src/lib.rs
@@ -7,6 +7,7 @@ use codex_config::NoopThreadConfigLoader;
 use codex_config::RemoteThreadConfigLoader;
 use codex_config::ThreadConfigLoader;
 use codex_core::config::Config;
+use codex_core::resolve_installation_id;
 use codex_exec_server::EnvironmentManagerArgs;
 use codex_features::Feature;
 use codex_login::AuthManager;
@@ -754,6 +755,7 @@ pub async fn run_main_with_transport_options(
             AuthManager::shared_from_config(&config, /*enable_codex_api_key_env*/ false).await;
         let analytics_events_client =
             analytics_events_client_from_config(Arc::clone(&auth_manager), &config);
+        let installation_id = resolve_installation_id(&config.codex_home).await?;
         let outgoing_message_sender = Arc::new(OutgoingMessageSender::new(
             outgoing_tx,
             analytics_events_client.clone(),
@@ -773,6 +775,7 @@ pub async fn run_main_with_transport_options(
             config_warnings,
             session_source,
             auth_manager,
+            installation_id,
             rpc_transport: analytics_rpc_transport(&transport),
             remote_control_handle: Some(remote_control_handle.clone()),
             plugin_startup_tasks: runtime_options.plugin_startup_tasks,
diff --git a/codex-rs/app-server/src/message_processor.rs b/codex-rs/app-server/src/message_processor.rs
index 308fd8f1e6..b60c10ef00 100644
--- a/codex-rs/app-server/src/message_processor.rs
+++ b/codex-rs/app-server/src/message_processor.rs
@@ -258,6 +258,7 @@ pub(crate) struct MessageProcessorArgs {
     pub(crate) config_warnings: Vec<ConfigWarningNotification>,
     pub(crate) session_source: SessionSource,
     pub(crate) auth_manager: Arc<AuthManager>,
+    pub(crate) installation_id: String,
     pub(crate) rpc_transport: AppServerRpcTransport,
     pub(crate) remote_control_handle: Option<RemoteControlHandle>,
     pub(crate) plugin_startup_tasks: crate::PluginStartupTasks,
@@ -280,6 +281,7 @@ impl MessageProcessor {
             config_warnings,
             session_source,
             auth_manager,
+            installation_id,
             rpc_transport,
             remote_control_handle,
             plugin_startup_tasks,
@@ -299,6 +301,7 @@ impl MessageProcessor {
             Some(analytics_events_client.clone()),
             Arc::clone(&thread_store),
             state_db.clone(),
+            installation_id,
         ));
         thread_manager
             .plugins_manager()
diff --git a/codex-rs/app-server/src/message_processor_tracing_tests.rs b/codex-rs/app-server/src/message_processor_tracing_tests.rs
index 45ea709180..0d4ef8279b 100644
--- a/codex-rs/app-server/src/message_processor_tracing_tests.rs
+++ b/codex-rs/app-server/src/message_processor_tracing_tests.rs
@@ -294,6 +294,7 @@ async fn build_test_processor(
         config_warnings: Vec::new(),
         session_source: SessionSource::VSCode,
         auth_manager,
+        installation_id: "11111111-1111-4111-8111-111111111111".to_string(),
         rpc_transport: AppServerRpcTransport::Stdio,
         remote_control_handle: None,
         plugin_startup_tasks: crate::PluginStartupTasks::Start,
diff --git a/codex-rs/core-api/src/lib.rs b/codex-rs/core-api/src/lib.rs
index aa68656d1b..995de1c650 100644
--- a/codex-rs/core-api/src/lib.rs
+++ b/codex-rs/core-api/src/lib.rs
@@ -39,6 +39,7 @@ pub use codex_core::config::TerminalResizeReflowConfig;
 pub use codex_core::config::ThreadStoreConfig;
 pub use codex_core::config::find_codex_home;
 pub use codex_core::init_state_db;
+pub use codex_core::resolve_installation_id;
 pub use codex_core::skills::SkillsManager;
 pub use codex_core::thread_store_from_config;
 pub use codex_exec_server::EnvironmentManager;
diff --git a/codex-rs/core/src/codex_delegate.rs b/codex-rs/core/src/codex_delegate.rs
index 1aeb125091..866a34ce35 100644
--- a/codex-rs/core/src/codex_delegate.rs
+++ b/codex-rs/core/src/codex_delegate.rs
@@ -75,6 +75,7 @@ pub(crate) async fn run_codex_thread_interactive(
     let (tx_ops, rx_ops) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
     let CodexSpawnOk { codex, .. } = Box::pin(Codex::spawn(CodexSpawnArgs {
         config,
+        installation_id: parent_session.installation_id.clone(),
         auth_manager,
         models_manager,
         environment_manager: Arc::clone(&parent_session.services.environment_manager),
diff --git a/codex-rs/core/src/prompt_debug.rs b/codex-rs/core/src/prompt_debug.rs
index 7c6144c10e..8717427afe 100644
--- a/codex-rs/core/src/prompt_debug.rs
+++ b/codex-rs/core/src/prompt_debug.rs
@@ -13,6 +13,7 @@ use codex_protocol::user_input::UserInput;
 use tokio_util::sync::CancellationToken;
 
 use crate::config::Config;
+use crate::resolve_installation_id;
 use crate::session::session::Session;
 use crate::session::turn::build_prompt;
 use crate::session::turn::built_tools;
@@ -38,6 +39,7 @@ pub async fn build_prompt_input(
     )?;
 
     let thread_store = thread_store_from_config(&config, state_db.clone());
+    let installation_id = resolve_installation_id(&config.codex_home).await?;
     let thread_manager = ThreadManager::new(
         &config,
         Arc::clone(&auth_manager),
@@ -46,6 +48,7 @@ pub async fn build_prompt_input(
         /*analytics_events_client*/ None,
         thread_store,
         state_db.clone(),
+        installation_id,
     );
     let thread = thread_manager.start_thread(config).await?;
 
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index 0da9968149..b5dd7af23b 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -32,7 +32,6 @@ use crate::context::PersonalitySpecInstructions;
 use crate::default_skill_metadata_budget;
 use crate::environment_selection::ResolvedTurnEnvironments;
 use crate::exec_policy::ExecPolicyManager;
-use crate::installation_id::resolve_installation_id;
 use crate::parse_turn_item;
 use crate::path_utils::normalize_for_native_workdir;
 use crate::realtime_conversation::RealtimeConversationManager;
@@ -388,6 +387,7 @@ pub struct CodexSpawnOk {
 
 pub(crate) struct CodexSpawnArgs {
     pub(crate) config: Config,
+    pub(crate) installation_id: String,
     pub(crate) auth_manager: Arc<AuthManager>,
     pub(crate) models_manager: SharedModelsManager,
     pub(crate) environment_manager: Arc<EnvironmentManager>,
@@ -449,6 +449,7 @@ impl Codex {
     async fn spawn_internal(args: CodexSpawnArgs) -> CodexResult<CodexSpawnOk> {
         let CodexSpawnArgs {
             mut config,
+            installation_id,
             auth_manager,
             models_manager,
             environment_manager,
@@ -637,6 +638,7 @@ impl Codex {
         let session = Session::new(
             session_configuration,
             config.clone(),
+            installation_id,
             auth_manager.clone(),
             models_manager.clone(),
             exec_policy,
diff --git a/codex-rs/core/src/session/session.rs b/codex-rs/core/src/session/session.rs
index 2444ded83f..02a1f1ee3f 100644
--- a/codex-rs/core/src/session/session.rs
+++ b/codex-rs/core/src/session/session.rs
@@ -11,6 +11,7 @@ use tokio::sync::Semaphore;
 /// A session has at most 1 running task at a time, and can be interrupted by user input.
 pub(crate) struct Session {
     pub(crate) conversation_id: ThreadId,
+    pub(crate) installation_id: String,
     pub(super) tx_event: Sender<Event>,
     pub(super) agent_status: watch::Sender<AgentStatus>,
     pub(super) out_of_band_elicitation_paused: watch::Sender<bool>,
@@ -330,6 +331,7 @@ impl Session {
     pub(crate) async fn new(
         mut session_configuration: SessionConfiguration,
         config: Arc<Config>,
+        installation_id: String,
         auth_manager: Arc<AuthManager>,
         models_manager: SharedModelsManager,
         exec_policy: Arc<ExecPolicyManager>,
@@ -815,7 +817,6 @@ impl Session {
                 });
             }
 
-            let installation_id = resolve_installation_id(&config.codex_home).await?;
             let analytics_events_client = analytics_events_client.unwrap_or_else(|| {
                 AnalyticsEventsClient::new(
                     Arc::clone(&auth_manager),
@@ -868,7 +869,7 @@ impl Session {
                 model_client: ModelClient::new(
                     Some(Arc::clone(&auth_manager)),
                     conversation_id,
-                    installation_id,
+                    installation_id.clone(),
                     session_configuration.provider.clone(),
                     session_configuration.session_source.clone(),
                     config.model_verbosity,
@@ -888,6 +889,7 @@ impl Session {
             let (mailbox, mailbox_rx) = Mailbox::new();
             let sess = Arc::new(Session {
                 conversation_id,
+                installation_id,
                 tx_event: tx_event.clone(),
                 agent_status,
                 out_of_band_elicitation_paused,
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index 0a8ea46f81..0b79c2865b 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -3476,6 +3476,7 @@ async fn session_new_fails_when_zsh_fork_enabled_without_zsh_path() {
     let result = Session::new(
         session_configuration,
         Arc::clone(&config),
+        "11111111-1111-4111-8111-111111111111".to_string(),
         auth_manager,
         models_manager,
         Arc::new(ExecPolicyManager::default()),
@@ -3695,6 +3696,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
     let (mailbox, mailbox_rx) = crate::agent::Mailbox::new();
     let session = Session {
         conversation_id,
+        installation_id: "11111111-1111-4111-8111-111111111111".to_string(),
         tx_event,
         agent_status: agent_status_tx,
         out_of_band_elicitation_paused: watch::channel(false).0,
@@ -3796,6 +3798,7 @@ async fn make_session_with_config_and_rx(
     let session = Session::new(
         session_configuration,
         Arc::clone(&config),
+        "11111111-1111-4111-8111-111111111111".to_string(),
         auth_manager,
         models_manager,
         Arc::new(ExecPolicyManager::default()),
@@ -5223,6 +5226,7 @@ where
     let (mailbox, mailbox_rx) = crate::agent::Mailbox::new();
     let session = Arc::new(Session {
         conversation_id,
+        installation_id: "11111111-1111-4111-8111-111111111111".to_string(),
         tx_event,
         agent_status: agent_status_tx,
         out_of_band_elicitation_paused: watch::channel(false).0,
diff --git a/codex-rs/core/src/session/tests/guardian_tests.rs b/codex-rs/core/src/session/tests/guardian_tests.rs
index ad7dbb1054..d03d4368a4 100644
--- a/codex-rs/core/src/session/tests/guardian_tests.rs
+++ b/codex-rs/core/src/session/tests/guardian_tests.rs
@@ -736,6 +736,7 @@ async fn guardian_subagent_does_not_inherit_parent_exec_policy_rules() {
 
     let CodexSpawnOk { codex, .. } = Codex::spawn(CodexSpawnArgs {
         config,
+        installation_id: "11111111-1111-4111-8111-111111111111".to_string(),
         auth_manager,
         models_manager,
         environment_manager: Arc::new(EnvironmentManager::default_for_tests()),
diff --git a/codex-rs/core/src/thread_manager.rs b/codex-rs/core/src/thread_manager.rs
index d4e36ab3c8..0cd88e26da 100644
--- a/codex-rs/core/src/thread_manager.rs
+++ b/codex-rs/core/src/thread_manager.rs
@@ -248,6 +248,7 @@ pub(crate) struct ThreadManagerState {
     skills_watcher: Arc<SkillsWatcher>,
     thread_store: Arc<dyn ThreadStore>,
     session_source: SessionSource,
+    installation_id: String,
     analytics_events_client: Option<AnalyticsEventsClient>,
     state_db: Option<StateDbHandle>,
     // Captures submitted ops for testing purpose when test mode is enabled.
@@ -280,6 +281,7 @@ pub fn thread_store_from_config(
 }
 
 impl ThreadManager {
+    #[allow(clippy::too_many_arguments)]
     pub fn new(
         config: &Config,
         auth_manager: Arc<AuthManager>,
@@ -288,6 +290,7 @@ impl ThreadManager {
         analytics_events_client: Option<AnalyticsEventsClient>,
         thread_store: Arc<dyn ThreadStore>,
         state_db: Option<StateDbHandle>,
+        installation_id: String,
     ) -> Self {
         let codex_home = config.codex_home.clone();
         let restriction_product = session_source.restriction_product();
@@ -316,6 +319,7 @@ impl ThreadManager {
                 thread_store,
                 auth_manager,
                 session_source,
+                installation_id,
                 analytics_events_client,
                 state_db,
                 ops_log: should_use_test_thread_manager_behavior()
@@ -415,6 +419,7 @@ impl ThreadManager {
                 thread_store,
                 auth_manager,
                 session_source: SessionSource::Exec,
+                installation_id: uuid::Uuid::new_v4().to_string(),
                 analytics_events_client: None,
                 state_db,
                 ops_log: should_use_test_thread_manager_behavior()
@@ -1152,6 +1157,7 @@ impl ThreadManagerState {
             codex, thread_id, ..
         } = Codex::spawn(CodexSpawnArgs {
             config,
+            installation_id: self.installation_id.clone(),
             auth_manager,
             models_manager: Arc::clone(&self.models_manager),
             environment_manager: Arc::clone(&self.environment_manager),
diff --git a/codex-rs/core/src/thread_manager_tests.rs b/codex-rs/core/src/thread_manager_tests.rs
index d50a3ae8f9..5d2832fe6c 100644
--- a/codex-rs/core/src/thread_manager_tests.rs
+++ b/codex-rs/core/src/thread_manager_tests.rs
@@ -1,6 +1,7 @@
 use super::*;
 use crate::config::test_config;
 use crate::init_state_db;
+use crate::installation_id::INSTALLATION_ID_FILENAME;
 use crate::rollout::RolloutRecorder;
 use crate::session::session::SessionSettingsUpdate;
 use crate::session::tests::make_session_and_context;
@@ -26,6 +27,8 @@ use std::time::Duration;
 use tempfile::tempdir;
 use wiremock::MockServer;
 
+const TEST_INSTALLATION_ID: &str = "11111111-1111-4111-8111-111111111111";
+
 fn user_msg(text: &str) -> ResponseItem {
     ResponseItem::Message {
         id: None,
@@ -392,6 +395,7 @@ async fn resume_and_fork_do_not_restore_thread_environments_from_rollout() {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, /*state_db*/ None),
         /*state_db*/ None,
+        TEST_INSTALLATION_ID.to_string(),
     );
     let selected_cwd =
         AbsolutePathBuf::try_from(config.cwd.as_path().join("selected")).expect("absolute path");
@@ -484,6 +488,44 @@ async fn resume_and_fork_do_not_restore_thread_environments_from_rollout() {
     );
 }
 
+#[tokio::test]
+async fn explicit_installation_id_skips_codex_home_file() {
+    let temp_dir = tempdir().expect("tempdir");
+    let mut config = test_config().await;
+    config.codex_home = temp_dir.path().join("codex-home").abs();
+    config.cwd = config.codex_home.abs();
+    std::fs::create_dir_all(&config.codex_home).expect("create codex home");
+
+    let auth_manager =
+        AuthManager::from_auth_for_testing(CodexAuth::create_dummy_chatgpt_auth_for_testing());
+    let installation_id = uuid::Uuid::new_v4().to_string();
+    let manager = ThreadManager::new(
+        &config,
+        auth_manager,
+        SessionSource::Exec,
+        Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
+        /*analytics_events_client*/ None,
+        thread_store_from_config(&config, /*state_db*/ None),
+        /*state_db*/ None,
+        installation_id.clone(),
+    );
+
+    let thread = manager
+        .start_thread(config.clone())
+        .await
+        .expect("start thread with explicit installation id");
+
+    assert!(!config.codex_home.join(INSTALLATION_ID_FILENAME).exists());
+    assert_eq!(thread.thread.codex.session.installation_id, installation_id);
+
+    thread
+        .thread
+        .shutdown_and_wait()
+        .await
+        .expect("shutdown thread");
+    let _ = manager.remove_thread(&thread.thread_id).await;
+}
+
 #[tokio::test]
 async fn resume_active_thread_from_rollout_returns_running_thread() {
     let temp_dir = tempdir().expect("tempdir");
@@ -502,6 +544,7 @@ async fn resume_active_thread_from_rollout_returns_running_thread() {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, /*state_db*/ None),
         /*state_db*/ None,
+        TEST_INSTALLATION_ID.to_string(),
     );
 
     let source = manager
@@ -556,6 +599,7 @@ async fn resume_stopped_thread_from_rollout_spawns_new_thread() {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, /*state_db*/ None),
         /*state_db*/ None,
+        TEST_INSTALLATION_ID.to_string(),
     );
 
     let source = manager
@@ -620,6 +664,7 @@ async fn new_uses_active_provider_for_model_refresh() {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, /*state_db*/ None),
         /*state_db*/ None,
+        TEST_INSTALLATION_ID.to_string(),
     );
 
     let _ = manager.list_models(RefreshStrategy::Online).await;
@@ -833,6 +878,7 @@ async fn interrupted_fork_snapshot_does_not_synthesize_turn_id_for_legacy_histor
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, state_db.clone()),
         state_db.clone(),
+        TEST_INSTALLATION_ID.to_string(),
     );
 
     let source = manager
@@ -937,6 +983,7 @@ async fn interrupted_fork_snapshot_preserves_explicit_turn_id() {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, state_db.clone()),
         state_db.clone(),
+        TEST_INSTALLATION_ID.to_string(),
     );
 
     let source = manager
@@ -1030,6 +1077,7 @@ async fn interrupted_fork_snapshot_uses_persisted_mid_turn_history_without_live_
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, state_db.clone()),
         state_db.clone(),
+        TEST_INSTALLATION_ID.to_string(),
     );
 
     let source = manager
@@ -1168,6 +1216,7 @@ async fn resumed_thread_keeps_paused_goal_paused() -> anyhow::Result<()> {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, state_db.clone()),
         state_db.clone(),
+        TEST_INSTALLATION_ID.to_string(),
     );
 
     let source = manager
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 88c1698d8f..6f44673f13 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
@@ -3166,6 +3166,7 @@ async fn tool_handlers_cascade_close_and_resume_and_keep_explicitly_closed_subtr
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, state_db.clone()),
         state_db.clone(),
+        "11111111-1111-4111-8111-111111111111".to_string(),
     );
 
     let parent = manager
diff --git a/codex-rs/core/tests/common/test_codex.rs b/codex-rs/core/tests/common/test_codex.rs
index 14f652f58b..ded994dbdb 100644
--- a/codex-rs/core/tests/common/test_codex.rs
+++ b/codex-rs/core/tests/common/test_codex.rs
@@ -16,6 +16,7 @@ use codex_config::CloudRequirementsLoader;
 use codex_core::CodexThread;
 use codex_core::ThreadManager;
 use codex_core::config::Config;
+use codex_core::resolve_installation_id;
 use codex_core::shell::Shell;
 use codex_core::shell::get_shell_by_model_provided_path;
 use codex_core::thread_store_from_config;
@@ -424,25 +425,18 @@ impl TestCodexBuilder {
     ) -> anyhow::Result<TestCodex> {
         let auth = self.auth.clone();
         let state_db = codex_core::init_state_db(&config).await;
-        let thread_manager = if config.model_catalog.is_some() {
-            ThreadManager::new(
-                &config,
-                codex_core::test_support::auth_manager_from_auth(auth.clone()),
-                SessionSource::Exec,
-                Arc::clone(&environment_manager),
-                /*analytics_events_client*/ None,
-                thread_store_from_config(&config, state_db.clone()),
-                state_db.clone(),
-            )
-        } else {
-            codex_core::test_support::thread_manager_with_models_provider_home_and_state(
-                auth.clone(),
-                config.model_provider.clone(),
-                config.codex_home.to_path_buf(),
-                Arc::clone(&environment_manager),
-                state_db.clone(),
-            )
-        };
+        codex_core::test_support::set_thread_manager_test_mode(true);
+        let installation_id = resolve_installation_id(&config.codex_home).await?;
+        let thread_manager = ThreadManager::new(
+            &config,
+            codex_core::test_support::auth_manager_from_auth(auth.clone()),
+            SessionSource::Exec,
+            Arc::clone(&environment_manager),
+            /*analytics_events_client*/ None,
+            thread_store_from_config(&config, state_db.clone()),
+            state_db.clone(),
+            installation_id,
+        );
         let thread_manager = Arc::new(thread_manager);
         let user_shell_override = self.user_shell_override.clone();
 
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index afa586a158..cf91b5ebfb 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -5,6 +5,7 @@ use codex_core::NewThread;
 use codex_core::Prompt;
 use codex_core::ResponseEvent;
 use codex_core::ThreadManager;
+use codex_core::resolve_installation_id;
 use codex_core::thread_store_from_config;
 use codex_features::Feature;
 use codex_login::AuthManager;
@@ -1106,6 +1107,9 @@ async fn prefers_apikey_when_config_prefers_apikey_even_with_chatgpt_tokens() {
         Ok(None) => panic!("No CodexAuth found in codex_home"),
         Err(e) => panic!("Failed to load CodexAuth: {e}"),
     };
+    let installation_id = resolve_installation_id(&config.codex_home)
+        .await
+        .expect("resolve installation id");
     let thread_manager = ThreadManager::new(
         &config,
         auth_manager,
@@ -1114,6 +1118,7 @@ async fn prefers_apikey_when_config_prefers_apikey_even_with_chatgpt_tokens() {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, /*state_db*/ None),
         /*state_db*/ None,
+        installation_id,
     );
     let NewThread { thread: codex, .. } = thread_manager
         .start_thread(config.clone())
diff --git a/codex-rs/core/tests/suite/skills.rs b/codex-rs/core/tests/suite/skills.rs
index add1ee6ea7..78bb3bcac7 100644
--- a/codex-rs/core/tests/suite/skills.rs
+++ b/codex-rs/core/tests/suite/skills.rs
@@ -248,6 +248,7 @@ async fn list_skills_skips_cwd_roots_when_environment_disabled() -> Result<()> {
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, /*state_db*/ None),
         /*state_db*/ None,
+        "11111111-1111-4111-8111-111111111111".to_string(),
     );
     let new_thread = thread_manager.start_thread(config.clone()).await?;
     let cwd = config.cwd.to_path_buf();
diff --git a/codex-rs/mcp-server/src/lib.rs b/codex-rs/mcp-server/src/lib.rs
index 75372c6e7c..ea77013046 100644
--- a/codex-rs/mcp-server/src/lib.rs
+++ b/codex-rs/mcp-server/src/lib.rs
@@ -114,6 +114,16 @@ pub async fn run_main(
     let (incoming_tx, mut incoming_rx) = mpsc::channel::<IncomingMessage>(CHANNEL_CAPACITY);
     let (outgoing_tx, mut outgoing_rx) = mpsc::unbounded_channel::<OutgoingMessage>();
 
+    let outgoing_message_sender = OutgoingMessageSender::new(outgoing_tx);
+    let mut processor = MessageProcessor::new(
+        outgoing_message_sender,
+        arg0_paths,
+        Arc::new(config),
+        environment_manager,
+        state_db,
+    )
+    .await?;
+
     // Task: read from stdin, push to `incoming_tx`.
     let stdin_reader_handle = tokio::spawn({
         async move {
@@ -138,28 +148,17 @@ pub async fn run_main(
     });
 
     // Task: process incoming messages.
-    let processor_handle = tokio::spawn({
-        let outgoing_message_sender = OutgoingMessageSender::new(outgoing_tx);
-        let mut processor = MessageProcessor::new(
-            outgoing_message_sender,
-            arg0_paths,
-            Arc::new(config),
-            environment_manager,
-            state_db,
-        )
-        .await;
-        async move {
-            while let Some(msg) = incoming_rx.recv().await {
-                match msg {
-                    JsonRpcMessage::Request(r) => processor.process_request(r).await,
-                    JsonRpcMessage::Response(r) => processor.process_response(r).await,
-                    JsonRpcMessage::Notification(n) => processor.process_notification(n).await,
-                    JsonRpcMessage::Error(e) => processor.process_error(e),
-                }
+    let processor_handle = tokio::spawn(async move {
+        while let Some(msg) = incoming_rx.recv().await {
+            match msg {
+                JsonRpcMessage::Request(r) => processor.process_request(r).await,
+                JsonRpcMessage::Response(r) => processor.process_response(r).await,
+                JsonRpcMessage::Notification(n) => processor.process_notification(n).await,
+                JsonRpcMessage::Error(e) => processor.process_error(e),
             }
-
-            info!("processor task exited (channel closed)");
         }
+
+        info!("processor task exited (channel closed)");
     });
 
     // Task: write outgoing messages to stdout.
diff --git a/codex-rs/mcp-server/src/message_processor.rs b/codex-rs/mcp-server/src/message_processor.rs
index 9ce46dfeda..a024406689 100644
--- a/codex-rs/mcp-server/src/message_processor.rs
+++ b/codex-rs/mcp-server/src/message_processor.rs
@@ -5,6 +5,7 @@ use codex_arg0::Arg0DispatchPaths;
 use codex_core::StateDbHandle;
 use codex_core::ThreadManager;
 use codex_core::config::Config;
+use codex_core::resolve_installation_id;
 use codex_core::thread_store_from_config;
 use codex_exec_server::EnvironmentManager;
 use codex_login::AuthManager;
@@ -55,13 +56,14 @@ impl MessageProcessor {
         config: Arc<Config>,
         environment_manager: Arc<EnvironmentManager>,
         state_db: Option<StateDbHandle>,
-    ) -> Self {
+    ) -> std::io::Result<Self> {
         let outgoing = Arc::new(outgoing);
         let auth_manager = AuthManager::shared_from_config(
             config.as_ref(),
             /*enable_codex_api_key_env*/ false,
         )
         .await;
+        let installation_id = resolve_installation_id(&config.codex_home).await?;
         let thread_manager = Arc::new(ThreadManager::new(
             config.as_ref(),
             auth_manager,
@@ -70,14 +72,15 @@ impl MessageProcessor {
             /*analytics_events_client*/ None,
             thread_store_from_config(config.as_ref(), state_db.clone()),
             state_db.clone(),
+            installation_id,
         ));
-        Self {
+        Ok(Self {
             outgoing,
             initialized: false,
             arg0_paths,
             thread_manager,
             running_requests_id_to_codex_uuid: Arc::new(Mutex::new(HashMap::new())),
-        }
+        })
     }
 
     pub(crate) async fn process_request(&mut self, request: JsonRpcRequest<ClientRequest>) {
diff --git a/codex-rs/thread-manager-sample/src/main.rs b/codex-rs/thread-manager-sample/src/main.rs
index 7064d9e4ce..58ace9d00b 100644
--- a/codex-rs/thread-manager-sample/src/main.rs
+++ b/codex-rs/thread-manager-sample/src/main.rs
@@ -56,6 +56,7 @@ use codex_core_api::built_in_model_providers;
 use codex_core_api::find_codex_home;
 use codex_core_api::init_state_db;
 use codex_core_api::item_event_to_server_notification;
+use codex_core_api::resolve_installation_id;
 use codex_core_api::set_default_originator;
 use codex_core_api::thread_store_from_config;
 
@@ -114,6 +115,7 @@ async fn run_main(arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
     let thread_store = thread_store_from_config(&config, state_db.clone());
     let environment_manager =
         Arc::new(EnvironmentManager::new(EnvironmentManagerArgs::new(local_runtime_paths)).await);
+    let installation_id = resolve_installation_id(&config.codex_home).await?;
     let thread_manager = ThreadManager::new(
         &config,
         auth_manager,
@@ -122,6 +124,7 @@ async fn run_main(arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
         /*analytics_events_client*/ None,
         Arc::clone(&thread_store),
         state_db,
+        installation_id,
     );
 
     let NewThread {