diff --git a/codex-rs/app-server/tests/common/Cargo.toml b/codex-rs/app-server/tests/common/Cargo.toml
index d91ed4e675..de58509f0d 100644
--- a/codex-rs/app-server/tests/common/Cargo.toml
+++ b/codex-rs/app-server/tests/common/Cargo.toml
@@ -12,7 +12,7 @@ anyhow = { workspace = true }
 base64 = { workspace = true }
 chrono = { workspace = true }
 codex-app-server-protocol = { workspace = true }
-codex-core = { workspace = true, features = ["test-support"] }
+codex-core = { workspace = true }
 codex-protocol = { workspace = true }
 codex-utils-cargo-bin = { workspace = true }
 serde = { workspace = true }
diff --git a/codex-rs/core/BUILD.bazel b/codex-rs/core/BUILD.bazel
index 6e5ce680ae..2ef299c5c0 100644
--- a/codex-rs/core/BUILD.bazel
+++ b/codex-rs/core/BUILD.bazel
@@ -3,10 +3,6 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "core",
     crate_name = "codex_core",
-    # TODO(mbolin): Eliminate the use of features in the version of the
-    # rust_library() that is used by rust_binary() rules for release artifacts
-    # such as the Codex CLI.
-    crate_features = ["test-support"],
     compile_data = glob(
         include = ["**"],
         exclude = [
diff --git a/codex-rs/core/Cargo.toml b/codex-rs/core/Cargo.toml
index 26e7f17cc8..e759072fac 100644
--- a/codex-rs/core/Cargo.toml
+++ b/codex-rs/core/Cargo.toml
@@ -113,10 +113,6 @@ which = { workspace = true }
 wildmatch = { workspace = true }
 zip = { workspace = true }
 
-[features]
-test-support = []
-
-
 [target.'cfg(target_os = "linux")'.dependencies]
 keyring = { workspace = true, features = ["linux-native-async-persistent"] }
 landlock = { workspace = true }
diff --git a/codex-rs/core/src/auth.rs b/codex-rs/core/src/auth.rs
index a6282305ea..198af0bbce 100644
--- a/codex-rs/core/src/auth.rs
+++ b/codex-rs/core/src/auth.rs
@@ -981,8 +981,8 @@ impl AuthManager {
         }
     }
 
-    #[cfg(any(test, feature = "test-support"))]
     /// Create an AuthManager with a specific CodexAuth, for testing only.
+    #[doc(hidden)]
     pub fn from_auth_for_testing(auth: CodexAuth) -> Arc<Self> {
         let cached = CachedAuth {
             auth: Some(auth),
@@ -998,8 +998,8 @@ impl AuthManager {
         })
     }
 
-    #[cfg(any(test, feature = "test-support"))]
     /// Create an AuthManager with a specific CodexAuth and codex home, for testing only.
+    #[doc(hidden)]
     pub fn from_auth_for_testing_with_home(auth: CodexAuth, codex_home: PathBuf) -> Arc<Self> {
         let cached = CachedAuth {
             auth: Some(auth),
diff --git a/codex-rs/core/src/lib.rs b/codex-rs/core/src/lib.rs
index 85095bc5f5..39ea4d34ee 100644
--- a/codex-rs/core/src/lib.rs
+++ b/codex-rs/core/src/lib.rs
@@ -143,9 +143,11 @@ pub use exec_policy::check_execpolicy_for_warnings;
 pub use exec_policy::load_exec_policy;
 pub use file_watcher::FileWatcherEvent;
 pub use safety::get_platform_sandbox;
+#[doc(hidden)]
+pub use thread_manager::set_thread_manager_test_mode_for_tests;
 pub use tools::spec::parse_tool_input_schema;
 pub use turn_metadata::build_turn_metadata_header;
-#[cfg(any(test, feature = "test-support"))]
+#[doc(hidden)]
 pub use unified_exec::set_deterministic_process_ids_for_tests;
 // Re-export the protocol types from the standalone `codex-protocol` crate so existing
 // `codex_core::protocol::...` references continue to work across the workspace.
diff --git a/codex-rs/core/src/models_manager/collaboration_mode_presets.rs b/codex-rs/core/src/models_manager/collaboration_mode_presets.rs
index cdc5134038..393762d8f5 100644
--- a/codex-rs/core/src/models_manager/collaboration_mode_presets.rs
+++ b/codex-rs/core/src/models_manager/collaboration_mode_presets.rs
@@ -13,7 +13,7 @@ pub(super) fn builtin_collaboration_mode_presets() -> Vec<CollaborationModeMask>
     vec![plan_preset(), default_preset()]
 }
 
-#[cfg(any(test, feature = "test-support"))]
+#[doc(hidden)]
 pub fn test_builtin_collaboration_mode_presets() -> Vec<CollaborationModeMask> {
     builtin_collaboration_mode_presets()
 }
diff --git a/codex-rs/core/src/models_manager/manager.rs b/codex-rs/core/src/models_manager/manager.rs
index d3bf497e63..b0e9ff2552 100644
--- a/codex-rs/core/src/models_manager/manager.rs
+++ b/codex-rs/core/src/models_manager/manager.rs
@@ -336,8 +336,8 @@ impl ModelsManager {
         }
     }
 
-    #[cfg(any(test, feature = "test-support"))]
     /// Construct a manager with a specific provider for testing.
+    #[doc(hidden)]
     pub fn with_provider(
         codex_home: PathBuf,
         auth_manager: Arc<AuthManager>,
@@ -355,8 +355,8 @@ impl ModelsManager {
         }
     }
 
-    #[cfg(any(test, feature = "test-support"))]
     /// Get model identifier without consulting remote state or cache.
+    #[doc(hidden)]
     pub fn get_model_offline(model: Option<&str>) -> String {
         if let Some(model) = model {
             return model.to_string();
@@ -370,8 +370,8 @@ impl ModelsManager {
             .unwrap_or_default()
     }
 
-    #[cfg(any(test, feature = "test-support"))]
     /// Build `ModelInfo` without consulting remote state or cache.
+    #[doc(hidden)]
     pub fn construct_model_info_offline(model: &str, config: &Config) -> ModelInfo {
         model_info::with_config_overrides(model_info::model_info_from_slug(model), config)
     }
diff --git a/codex-rs/core/src/models_manager/mod.rs b/codex-rs/core/src/models_manager/mod.rs
index 9527466252..3929ea367f 100644
--- a/codex-rs/core/src/models_manager/mod.rs
+++ b/codex-rs/core/src/models_manager/mod.rs
@@ -4,7 +4,6 @@ pub mod manager;
 pub mod model_info;
 pub mod model_presets;
 
-#[cfg(any(test, feature = "test-support"))]
 pub use collaboration_mode_presets::test_builtin_collaboration_mode_presets;
 
 /// Convert the client version string to a whole version string (e.g. "1.2.3-alpha.4" -> "1.2.3").
diff --git a/codex-rs/core/src/models_manager/model_presets.rs b/codex-rs/core/src/models_manager/model_presets.rs
index a597f7f922..b4c191603b 100644
--- a/codex-rs/core/src/models_manager/model_presets.rs
+++ b/codex-rs/core/src/models_manager/model_presets.rs
@@ -359,7 +359,7 @@ pub(super) fn builtin_model_presets(_auth_mode: Option<AuthMode>) -> Vec<ModelPr
     PRESETS.iter().cloned().collect()
 }
 
-#[cfg(any(test, feature = "test-support"))]
+#[doc(hidden)]
 pub fn all_model_presets() -> &'static Vec<ModelPreset> {
     &PRESETS
 }
diff --git a/codex-rs/core/src/thread_manager.rs b/codex-rs/core/src/thread_manager.rs
index 13f9efafb0..de89275e82 100644
--- a/codex-rs/core/src/thread_manager.rs
+++ b/codex-rs/core/src/thread_manager.rs
@@ -1,7 +1,5 @@
 use crate::AuthManager;
-#[cfg(any(test, feature = "test-support"))]
 use crate::CodexAuth;
-#[cfg(any(test, feature = "test-support"))]
 use crate::ModelProviderInfo;
 use crate::agent::AgentControl;
 use crate::codex::Codex;
@@ -31,25 +29,48 @@ use codex_protocol::protocol::SessionSource;
 use std::collections::HashMap;
 use std::path::PathBuf;
 use std::sync::Arc;
-#[cfg(any(test, feature = "test-support"))]
-use tempfile::TempDir;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
 use tokio::runtime::Handle;
-#[cfg(any(test, feature = "test-support"))]
 use tokio::runtime::RuntimeFlavor;
 use tokio::sync::RwLock;
 use tokio::sync::broadcast;
 use tracing::warn;
 
 const THREAD_CREATED_CHANNEL_CAPACITY: usize = 1024;
+/// Test-only override for enabling thread-manager behaviors used by integration
+/// tests.
+///
+/// In production builds this value should remain at its default (`false`) and
+/// must not be toggled.
+static FORCE_TEST_THREAD_MANAGER_BEHAVIOR: AtomicBool = AtomicBool::new(false);
+
+#[doc(hidden)]
+pub fn set_thread_manager_test_mode_for_tests(enabled: bool) {
+    FORCE_TEST_THREAD_MANAGER_BEHAVIOR.store(enabled, Ordering::Relaxed);
+}
+
+fn should_use_test_thread_manager_behavior() -> bool {
+    FORCE_TEST_THREAD_MANAGER_BEHAVIOR.load(Ordering::Relaxed)
+}
+
+struct TempCodexHomeGuard {
+    path: PathBuf,
+}
+
+impl Drop for TempCodexHomeGuard {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_dir_all(&self.path);
+    }
+}
 
 fn build_file_watcher(codex_home: PathBuf, skills_manager: Arc<SkillsManager>) -> Arc<FileWatcher> {
-    #[cfg(any(test, feature = "test-support"))]
-    if let Ok(handle) = Handle::try_current()
+    if should_use_test_thread_manager_behavior()
+        && let Ok(handle) = Handle::try_current()
         && handle.runtime_flavor() == RuntimeFlavor::CurrentThread
     {
         // The real watcher spins background tasks that can starve the
         // current-thread test runtime and cause event waits to time out.
-        // Integration tests compile with the `test-support` feature.
         warn!("using noop file watcher under current-thread test runtime");
         return Arc::new(FileWatcher::noop());
     }
@@ -95,8 +116,7 @@ pub struct NewThread {
 /// them in memory.
 pub struct ThreadManager {
     state: Arc<ThreadManagerState>,
-    #[cfg(any(test, feature = "test-support"))]
-    _test_codex_home_guard: Option<TempDir>,
+    _test_codex_home_guard: Option<TempCodexHomeGuard>,
 }
 
 /// Shared, `Arc`-owned state for [`ThreadManager`]. This `Arc` is required to have a single
@@ -110,10 +130,8 @@ pub(crate) struct ThreadManagerState {
     skills_manager: Arc<SkillsManager>,
     file_watcher: Arc<FileWatcher>,
     session_source: SessionSource,
-    #[cfg(any(test, feature = "test-support"))]
-    #[allow(dead_code)]
-    // Captures submitted ops for testing purpose.
-    ops_log: Arc<std::sync::Mutex<Vec<(ThreadId, Op)>>>,
+    // Captures submitted ops for testing purpose when test mode is enabled.
+    ops_log: Option<Arc<std::sync::Mutex<Vec<(ThreadId, Op)>>>>,
 }
 
 impl ThreadManager {
@@ -134,33 +152,38 @@ impl ThreadManager {
                 file_watcher,
                 auth_manager,
                 session_source,
-                #[cfg(any(test, feature = "test-support"))]
-                ops_log: Arc::new(std::sync::Mutex::new(Vec::new())),
+                ops_log: should_use_test_thread_manager_behavior()
+                    .then(|| Arc::new(std::sync::Mutex::new(Vec::new()))),
             }),
-            #[cfg(any(test, feature = "test-support"))]
             _test_codex_home_guard: None,
         }
     }
 
-    #[cfg(any(test, feature = "test-support"))]
     /// Construct with a dummy AuthManager containing the provided CodexAuth.
     /// Used for integration tests: should not be used by ordinary business logic.
+    #[doc(hidden)]
     pub fn with_models_provider(auth: CodexAuth, provider: ModelProviderInfo) -> Self {
-        let temp_dir = tempfile::tempdir().unwrap_or_else(|err| panic!("temp codex home: {err}"));
-        let codex_home = temp_dir.path().to_path_buf();
-        let mut manager = Self::with_models_provider_and_home(auth, provider, codex_home);
-        manager._test_codex_home_guard = Some(temp_dir);
+        set_thread_manager_test_mode_for_tests(true);
+        let codex_home = std::env::temp_dir().join(format!(
+            "codex-thread-manager-test-{}",
+            uuid::Uuid::new_v4()
+        ));
+        std::fs::create_dir_all(&codex_home)
+            .unwrap_or_else(|err| panic!("temp codex home dir create failed: {err}"));
+        let mut manager = Self::with_models_provider_and_home(auth, provider, codex_home.clone());
+        manager._test_codex_home_guard = Some(TempCodexHomeGuard { path: codex_home });
         manager
     }
 
-    #[cfg(any(test, feature = "test-support"))]
     /// Construct with a dummy AuthManager containing the provided CodexAuth and codex home.
     /// Used for integration tests: should not be used by ordinary business logic.
+    #[doc(hidden)]
     pub fn with_models_provider_and_home(
         auth: CodexAuth,
         provider: ModelProviderInfo,
         codex_home: PathBuf,
     ) -> Self {
+        set_thread_manager_test_mode_for_tests(true);
         let auth_manager = AuthManager::from_auth_for_testing(auth);
         let (thread_created_tx, _) = broadcast::channel(THREAD_CREATED_CHANNEL_CAPACITY);
         let skills_manager = Arc::new(SkillsManager::new(codex_home.clone()));
@@ -178,8 +201,8 @@ impl ThreadManager {
                 file_watcher,
                 auth_manager,
                 session_source: SessionSource::Exec,
-                #[cfg(any(test, feature = "test-support"))]
-                ops_log: Arc::new(std::sync::Mutex::new(Vec::new())),
+                ops_log: should_use_test_thread_manager_behavior()
+                    .then(|| Arc::new(std::sync::Mutex::new(Vec::new()))),
             }),
             _test_codex_home_guard: None,
         }
@@ -340,13 +363,13 @@ impl ThreadManager {
         AgentControl::new(Arc::downgrade(&self.state))
     }
 
-    #[cfg(any(test, feature = "test-support"))]
+    #[doc(hidden)]
     #[allow(dead_code)]
     pub(crate) fn captured_ops(&self) -> Vec<(ThreadId, Op)> {
         self.state
             .ops_log
-            .lock()
-            .map(|log| log.clone())
+            .as_ref()
+            .and_then(|ops_log| ops_log.lock().ok().map(|log| log.clone()))
             .unwrap_or_default()
     }
 }
@@ -364,11 +387,10 @@ impl ThreadManagerState {
     /// Send an operation to a thread by ID.
     pub(crate) async fn send_op(&self, thread_id: ThreadId, op: Op) -> CodexResult<String> {
         let thread = self.get_thread(thread_id).await?;
-        #[cfg(any(test, feature = "test-support"))]
+        if let Some(ops_log) = &self.ops_log
+            && let Ok(mut log) = ops_log.lock()
         {
-            if let Ok(mut log) = self.ops_log.lock() {
-                log.push((thread_id, op.clone()));
-            }
+            log.push((thread_id, op.clone()));
         }
         thread.submit(op).await
     }
diff --git a/codex-rs/core/src/unified_exec/mod.rs b/codex-rs/core/src/unified_exec/mod.rs
index bbc7790c63..3cd6813dd4 100644
--- a/codex-rs/core/src/unified_exec/mod.rs
+++ b/codex-rs/core/src/unified_exec/mod.rs
@@ -42,7 +42,6 @@ mod head_tail_buffer;
 mod process;
 mod process_manager;
 
-#[cfg(any(test, feature = "test-support"))]
 pub fn set_deterministic_process_ids_for_tests(enabled: bool) {
     process_manager::set_deterministic_process_ids_for_tests(enabled);
 }
diff --git a/codex-rs/core/src/unified_exec/process_manager.rs b/codex-rs/core/src/unified_exec/process_manager.rs
index 6740850092..251a4910ba 100644
--- a/codex-rs/core/src/unified_exec/process_manager.rs
+++ b/codex-rs/core/src/unified_exec/process_manager.rs
@@ -62,28 +62,20 @@ const UNIFIED_EXEC_ENV: [(&str, &str); 10] = [
     ("CODEX_CI", "1"),
 ];
 
-#[cfg(any(test, feature = "test-support"))]
 /// Test-only override for deterministic unified exec process IDs.
 ///
 /// In production builds this value should remain at its default (`false`) and
 /// must not be toggled.
 static FORCE_DETERMINISTIC_PROCESS_IDS: AtomicBool = AtomicBool::new(false);
 
-#[cfg(any(test, feature = "test-support"))]
 pub(super) fn set_deterministic_process_ids_for_tests(enabled: bool) {
     FORCE_DETERMINISTIC_PROCESS_IDS.store(enabled, Ordering::Relaxed);
 }
 
-#[cfg(any(test, feature = "test-support"))]
 fn deterministic_process_ids_forced_for_tests() -> bool {
     FORCE_DETERMINISTIC_PROCESS_IDS.load(Ordering::Relaxed)
 }
 
-#[cfg(not(any(test, feature = "test-support")))]
-fn deterministic_process_ids_forced_for_tests() -> bool {
-    false
-}
-
 fn should_use_deterministic_process_ids() -> bool {
     cfg!(test) || deterministic_process_ids_forced_for_tests()
 }
diff --git a/codex-rs/core/tests/common/Cargo.toml b/codex-rs/core/tests/common/Cargo.toml
index 1fb43bb768..a7d35c0de7 100644
--- a/codex-rs/core/tests/common/Cargo.toml
+++ b/codex-rs/core/tests/common/Cargo.toml
@@ -11,7 +11,7 @@ path = "lib.rs"
 anyhow = { workspace = true }
 assert_cmd = { workspace = true }
 base64 = { workspace = true }
-codex-core = { workspace = true, features = ["test-support"] }
+codex-core = { workspace = true }
 codex-protocol = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
 codex-utils-cargo-bin = { workspace = true }
diff --git a/codex-rs/core/tests/common/lib.rs b/codex-rs/core/tests/common/lib.rs
index 0144eeec5a..e81067d6c3 100644
--- a/codex-rs/core/tests/common/lib.rs
+++ b/codex-rs/core/tests/common/lib.rs
@@ -20,6 +20,7 @@ pub mod test_codex_exec;
 
 #[ctor]
 fn enable_deterministic_unified_exec_process_ids_for_tests() {
+    codex_core::set_thread_manager_test_mode_for_tests(true);
     codex_core::set_deterministic_process_ids_for_tests(true);
 }
 
diff --git a/codex-rs/tui/Cargo.toml b/codex-rs/tui/Cargo.toml
index 1dced39b76..5e313f19b1 100644
--- a/codex-rs/tui/Cargo.toml
+++ b/codex-rs/tui/Cargo.toml
@@ -120,7 +120,7 @@ arboard = { workspace = true }
 
 [dev-dependencies]
 codex-cli = { workspace = true }
-codex-core = { workspace = true, features = ["test-support"] }
+codex-core = { workspace = true }
 codex-utils-cargo-bin = { workspace = true }
 codex-utils-pty = { workspace = true }
 assert_matches = { workspace = true }