diff --git a/codex-rs/model-provider/src/shared_state_test_support.rs b/codex-rs/model-provider/src/shared_state_test_support.rs
index 38bc88b709..5a6d1fdafa 100644
--- a/codex-rs/model-provider/src/shared_state_test_support.rs
+++ b/codex-rs/model-provider/src/shared_state_test_support.rs
@@ -1,4 +1,4 @@
-//! Seeds encrypted gateway credentials for provider and agent integration tests.
+//! Seeds gateway credentials in the configured store for provider and agent integration tests.
 
 #![allow(clippy::expect_used)] // Fixture setup failures should fail the calling test immediately.
 
@@ -11,13 +11,12 @@ use codex_login::AuthManager;
 use codex_login::GatewayAuthConfig;
 use codex_login::GatewayAuthManager;
 use codex_model_provider_info::ModelProviderInfo;
+use codex_model_provider_info::OAuthCredentialsStore;
 use codex_secrets::LocalSecretsNamespace;
 use codex_secrets::SecretName;
 use codex_secrets::SecretScope;
 use codex_secrets::SecretsBackendKind;
 use codex_secrets::SecretsManager;
-use sha2::Digest;
-use sha2::Sha256;
 
 use super::process_shared_state;
 
@@ -59,7 +58,7 @@ impl KeyringStore for TestKeyring {
     }
 }
 
-/// Seeds a provider's encrypted gateway store with a test-only keyring passphrase.
+/// Seeds a provider's configured gateway store, using a test passphrase for the keyring backend.
 /// Keep the returned manager alive while requests use this fixture.
 pub fn seed_gateway_auth(
     info: &ModelProviderInfo,
@@ -85,43 +84,51 @@ pub fn seed_gateway_auth(
     let keyring = Arc::new(TestKeyring(Mutex::new(Some(
         "gateway-test-passphrase".to_string(),
     ))));
-    let secrets = SecretsManager::new_with_keyring_store_and_namespace(
-        runtime.codex_home.clone(),
-        SecretsBackendKind::Local,
-        keyring.clone(),
-        LocalSecretsNamespace::GatewayOAuth,
-    );
-    // Match the credential identity used by GatewayAuthManager's encrypted store.
-    let mut digest = Sha256::new();
-    digest.update(runtime.codex_home.to_string_lossy().as_bytes());
-    digest.update([0]);
-    for value in [
-        oauth.authorization_url.as_str(),
-        oauth.token_url.as_str(),
-        oauth.client_id.as_str(),
-        oauth.resource.as_deref().unwrap_or_default(),
-    ] {
-        digest.update(value.as_bytes());
-        digest.update([0]);
-    }
-    for scope in &oauth.scopes {
-        digest.update(scope.as_bytes());
-        digest.update([0]);
-    }
-    let name = SecretName::new(&format!("PROVIDER_OAUTH_{:X}", digest.finalize()))
-        .expect("gateway test credential name");
-    secrets
-        .set(&SecretScope::Global, &name, &token.to_string())
-        .expect("seed encrypted gateway credentials");
     let manager = Arc::new(
         GatewayAuthManager::new(
             oauth.clone(),
             runtime.codex_home.clone(),
             runtime.auth_route_config.http_client_factory(),
-            keyring,
+            keyring.clone(),
         )
         .expect("gateway test HTTP client"),
     );
+    let credential_id = manager.credential_id();
+    match oauth.credentials_store {
+        OAuthCredentialsStore::Keyring => {
+            let secrets = SecretsManager::new_with_keyring_store_and_namespace(
+                runtime.codex_home.clone(),
+                SecretsBackendKind::Local,
+                keyring,
+                LocalSecretsNamespace::GatewayOAuth,
+            );
+            let digest = credential_id
+                .strip_prefix("provider-oauth|")
+                .expect("gateway credential ID");
+            let name = SecretName::new(&format!("PROVIDER_OAUTH_{}", digest.to_ascii_uppercase()))
+                .expect("gateway test credential name");
+            secrets
+                .set(&SecretScope::Global, &name, &token.to_string())
+                .expect("seed encrypted gateway credentials");
+        }
+        OAuthCredentialsStore::File => {
+            let dir = runtime.codex_home.join("secrets");
+            std::fs::create_dir_all(&dir).expect("create test credentials directory");
+            let file = dir.join("gateway_oauth.json");
+            let mut tokens: std::collections::BTreeMap<String, serde_json::Value> =
+                match std::fs::read(&file) {
+                    Ok(bytes) => serde_json::from_slice(&bytes).expect("parse test gateway tokens"),
+                    Err(err) if err.kind() == std::io::ErrorKind::NotFound => Default::default(),
+                    Err(err) => panic!("read test gateway file: {err}"),
+                };
+            tokens.insert(credential_id, token);
+            std::fs::write(
+                file,
+                serde_json::to_vec(&tokens).expect("serialize test gateway tokens"),
+            )
+            .expect("seed test gateway file");
+        }
+    }
     process_shared_state()
         .gateway_managers
         .lock()
diff --git a/codex-rs/model-provider/src/shared_state_tests.rs b/codex-rs/model-provider/src/shared_state_tests.rs
index 7d06dfea34..3979a9988f 100644
--- a/codex-rs/model-provider/src/shared_state_tests.rs
+++ b/codex-rs/model-provider/src/shared_state_tests.rs
@@ -20,6 +20,7 @@ use codex_login::default_client::ClientRedirectPolicy;
 use codex_login::default_client::create_client_for_route;
 use codex_model_provider_info::GatewayOAuthDelivery;
 use codex_model_provider_info::ModelProviderInfo;
+use codex_model_provider_info::OAuthCredentialsStore;
 use codex_models_manager::manager::RefreshStrategy;
 use codex_protocol::error::CodexErrorDetails;
 use codex_protocol::protocol::CodexErrorInfo;
@@ -408,7 +409,8 @@ async fn models_cache_is_reused_only_for_matching_gateway_configuration() {
             resource: None,
             scopes: vec![],
             redirect_port: None,
-            credentials_store: Default::default(),
+            // Keyring latency is outside the cache behavior under test.
+            credentials_store: OAuthCredentialsStore::File,
             delivery: GatewayOAuthDelivery::Header {
                 name: "x-gateway-auth".into(),
                 scheme: "Bearer".into(),
@@ -672,7 +674,7 @@ async fn gateway_login_required_invalidates_the_last_successful_catalog() {
             resource: None,
             scopes: vec![],
             redirect_port: None,
-            credentials_store: Default::default(),
+            credentials_store: OAuthCredentialsStore::File,
             delivery: GatewayOAuthDelivery::Header {
                 name: "x-gateway-auth".into(),
                 scheme: "Bearer".into(),