changes

codex-rs/aws-auth/src/lib.rs

@@ -97,6 +97,11 @@ impl AwsAuthContext {
         &self.service
     }
 
+    pub async fn preload_credentials(&self) -> Result<(), AwsAuthError> {
+        let _ = self.credentials_provider.provide_credentials().await?;
+        Ok(())
+    }
+
     pub async fn sign(&self, request: AwsRequestToSign) -> Result<AwsSignedRequest, AwsAuthError> {
         self.sign_at(request, SystemTime::now()).await
     }
@@ -202,6 +207,14 @@ mod tests {
         assert!(signing::header_value(&signed.headers, "x-amz-date").is_some());
     }
 
+    #[tokio::test]
+    async fn preload_credentials_resolves_provider() {
+        test_context(/*session_token*/ None)
+            .preload_credentials()
+            .await
+            .expect("static credentials should resolve");
+    }
+
     #[test]
     fn credentials_provider_failures_are_retryable() {
         assert!(

codex-rs/core/src/client.rs

@@ -673,6 +673,15 @@ impl ModelClient {
         true
     }
 
+    /// Resolves provider credentials during session startup when the provider requests it.
+    pub(crate) async fn prewarm_provider_auth(&self) -> Result<()> {
+        if !self.state.provider.prewarms_auth_on_startup() {
+            return Ok(());
+        }
+
+        self.state.provider.prewarm_auth().await
+    }
+
     /// Returns auth + provider configuration resolved from the current session auth state.
     ///
     /// This centralizes setup used by both prewarm and normal request paths so they stay in

codex-rs/core/src/lib.rs

@@ -82,6 +82,7 @@ pub(crate) mod mentions {
 mod sandbox_tags;
 pub mod sandboxing;
 mod session_prefix;
+mod session_startup_auth_prewarm;
 mod session_startup_prewarm;
 mod shell_detect;
 pub mod skills;

codex-rs/core/src/session/session.rs

@@ -980,6 +980,7 @@ impl Session {
                     anyhow::bail!("required MCP servers failed to initialize: {details}");
                 }
             }
+            sess.schedule_startup_auth_prewarm().await;
             sess.schedule_startup_prewarm(session_configuration.base_instructions.clone())
                 .await;
             let session_start_source = match &initial_history {

codex-rs/core/src/session_startup_auth_prewarm.rs

@@ -0,0 +1,16 @@
+use std::sync::Arc;
+
+use tracing::debug;
+
+use crate::session::session::Session;
+
+impl Session {
+    pub(crate) async fn schedule_startup_auth_prewarm(self: &Arc<Self>) {
+        let model_client = self.services.model_client.clone();
+        tokio::spawn(async move {
+            if let Err(err) = model_client.prewarm_provider_auth().await {
+                debug!("startup provider auth prewarm failed: {err:#}");
+            }
+        });
+    }
+}

codex-rs/model-provider/src/amazon_bedrock/auth.rs

@@ -22,6 +22,7 @@ use super::mantle::region_from_config;
 const AWS_BEARER_TOKEN_BEDROCK_ENV_VAR: &str = "AWS_BEARER_TOKEN_BEDROCK";
 const LEGACY_SESSION_ID_HEADER: &str = "session_id";
 
+#[derive(Clone, Debug)]
 pub(super) enum BedrockAuthMethod {
     EnvBearerToken { token: String, region: String },
     AwsSdkAuth { context: AwsAuthContext },
@@ -42,17 +43,25 @@ pub(super) async fn resolve_auth_method(
     Ok(BedrockAuthMethod::AwsSdkAuth { context })
 }
 
-pub(super) async fn resolve_provider_auth(
-    aws: &ModelProviderAwsAuthInfo,
-) -> Result<SharedAuthProvider> {
-    match resolve_auth_method(aws).await? {
-        BedrockAuthMethod::EnvBearerToken { token, .. } => Ok(Arc::new(BearerAuthProvider {
+pub(super) async fn prewarm_credentials(auth_method: &BedrockAuthMethod) -> Result<()> {
+    match auth_method {
+        BedrockAuthMethod::EnvBearerToken { .. } => Ok(()),
+        BedrockAuthMethod::AwsSdkAuth { context } => context
+            .preload_credentials()
+            .await
+            .map_err(aws_auth_error_to_codex_error),
+    }
+}
+
+pub(super) fn provider_auth_from_method(auth_method: BedrockAuthMethod) -> SharedAuthProvider {
+    match auth_method {
+        BedrockAuthMethod::EnvBearerToken { token, .. } => Arc::new(BearerAuthProvider {
             token: Some(token),
             account_id: None,
             is_fedramp_account: false,
-        })),
+        }),
         BedrockAuthMethod::AwsSdkAuth { context } => {
-            Ok(Arc::new(BedrockMantleSigV4AuthProvider::new(context)))
+            Arc::new(BedrockMantleSigV4AuthProvider::new(context))
         }
     }
 }

codex-rs/model-provider/src/amazon_bedrock/mantle.rs

@@ -4,7 +4,6 @@ use codex_protocol::error::CodexErr;
 use codex_protocol::error::Result;
 
 use super::auth::BedrockAuthMethod;
-use super::auth::resolve_auth_method;
 
 const BEDROCK_MANTLE_SERVICE_NAME: &str = "bedrock-mantle";
 const BEDROCK_MANTLE_SUPPORTED_REGIONS: [&str; 12] = [
@@ -48,16 +47,15 @@ pub(super) fn base_url(region: &str) -> Result<String> {
     }
 }
 
-pub(super) async fn runtime_base_url(aws: &ModelProviderAwsAuthInfo) -> Result<String> {
-    let region = resolve_region(aws).await?;
-    base_url(&region)
+pub(super) fn region_from_auth_method(auth_method: &BedrockAuthMethod) -> String {
+    match auth_method {
+        BedrockAuthMethod::EnvBearerToken { region, .. } => region.clone(),
+        BedrockAuthMethod::AwsSdkAuth { context } => context.region().to_string(),
+    }
 }
 
-async fn resolve_region(aws: &ModelProviderAwsAuthInfo) -> Result<String> {
-    match resolve_auth_method(aws).await? {
-        BedrockAuthMethod::EnvBearerToken { region, .. } => Ok(region),
-        BedrockAuthMethod::AwsSdkAuth { context } => Ok(context.region().to_string()),
-    }
+pub(super) fn runtime_base_url_from_auth_method(auth_method: &BedrockAuthMethod) -> Result<String> {
+    base_url(&region_from_auth_method(auth_method))
 }
 
 #[cfg(test)]

codex-rs/model-provider/src/amazon_bedrock/mod.rs

@@ -16,20 +16,26 @@ use codex_models_manager::manager::StaticModelsManager;
 use codex_protocol::account::ProviderAccount;
 use codex_protocol::error::Result;
 use codex_protocol::openai_models::ModelsResponse;
+use tokio::sync::OnceCell;
 
 use crate::provider::ModelProvider;
 use crate::provider::ProviderAccountResult;
 use crate::provider::ProviderAccountState;
 use crate::provider::ProviderCapabilities;
-use auth::resolve_provider_auth;
+use auth::BedrockAuthMethod;
+use auth::prewarm_credentials;
+use auth::provider_auth_from_method;
+use auth::resolve_auth_method;
 pub(crate) use catalog::static_model_catalog;
-use mantle::runtime_base_url;
+use mantle::runtime_base_url_from_auth_method;
 
 /// Runtime provider for Amazon Bedrock's OpenAI-compatible Mantle endpoint.
 #[derive(Clone, Debug)]
 pub(crate) struct AmazonBedrockModelProvider {
     pub(crate) info: ModelProviderInfo,
     pub(crate) aws: ModelProviderAwsAuthInfo,
+    auth_method: Arc<OnceCell<BedrockAuthMethod>>,
+    credentials_prewarmed: Arc<OnceCell<()>>,
 }
 
 impl AmazonBedrockModelProvider {
@@ -44,8 +50,25 @@ impl AmazonBedrockModelProvider {
         Self {
             info: provider_info,
             aws,
+            auth_method: Arc::new(OnceCell::new()),
+            credentials_prewarmed: Arc::new(OnceCell::new()),
         }
     }
+
+    async fn auth_method(&self) -> Result<BedrockAuthMethod> {
+        self.auth_method
+            .get_or_try_init(|| resolve_auth_method(&self.aws))
+            .await
+            .cloned()
+    }
+
+    async fn prewarm_bedrock_credentials(&self) -> Result<()> {
+        let auth_method = self.auth_method().await?;
+        self.credentials_prewarmed
+            .get_or_try_init(|| async move { prewarm_credentials(&auth_method).await })
+            .await?;
+        Ok(())
+    }
 }
 
 #[async_trait::async_trait]
@@ -70,6 +93,14 @@ impl ModelProvider for AmazonBedrockModelProvider {
         None
     }
 
+    fn prewarms_auth_on_startup(&self) -> bool {
+        true
+    }
+
+    async fn prewarm_auth(&self) -> Result<()> {
+        self.prewarm_bedrock_credentials().await
+    }
+
     fn account_state(&self) -> ProviderAccountResult {
         Ok(ProviderAccountState {
             account: Some(ProviderAccount::AmazonBedrock),
@@ -79,16 +110,20 @@ impl ModelProvider for AmazonBedrockModelProvider {
 
     async fn api_provider(&self) -> Result<Provider> {
         let mut api_provider_info = self.info.clone();
-        api_provider_info.base_url = Some(runtime_base_url(&self.aws).await?);
+        api_provider_info.base_url = Some(runtime_base_url_from_auth_method(
+            &self.auth_method().await?,
+        )?);
         api_provider_info.to_api_provider(/*auth_mode*/ None)
     }
 
     async fn runtime_base_url(&self) -> Result<Option<String>> {
-        Ok(Some(runtime_base_url(&self.aws).await?))
+        Ok(Some(runtime_base_url_from_auth_method(
+            &self.auth_method().await?,
+        )?))
     }
 
     async fn api_auth(&self) -> Result<SharedAuthProvider> {
-        resolve_provider_auth(&self.aws).await
+        Ok(provider_auth_from_method(self.auth_method().await?))
     }
 
     fn models_manager(

codex-rs/model-provider/src/provider.rs

@@ -96,6 +96,16 @@ pub trait ModelProvider: fmt::Debug + Send + Sync {
     /// Returns the current provider-scoped auth value, if one is configured.
     async fn auth(&self) -> Option<CodexAuth>;
 
+    /// Returns whether this provider should resolve request credentials during session startup.
+    fn prewarms_auth_on_startup(&self) -> bool {
+        false
+    }
+
+    /// Resolves provider credentials before the first model request when startup prewarm is enabled.
+    async fn prewarm_auth(&self) -> codex_protocol::error::Result<()> {
+        Ok(())
+    }
+
     /// Returns the current app-visible account state for this provider.
     fn account_state(&self) -> ProviderAccountResult;