feat: update Bedrock Mantle endpoint and GPT-5.4 model ID (#20109)

## Summary

Amazon Bedrock Mantle's OpenAI-compatible endpoint now lives under
`/openai/v1`, and the GPT-5.4 Mantle model ID no longer uses the `-cmb`
suffix. This updates Codex's built-in Bedrock provider configuration so
generated providers and the static Bedrock catalog use the current
endpoint and model ID.

## Changes

- Update the Bedrock Mantle base URL from
`https://bedrock-mantle.{region}.api.aws/v1` to
`https://bedrock-mantle.{region}.api.aws/openai/v1`.
- Update the Amazon Bedrock default base URL in
`codex-model-provider-info`.
- Change the Bedrock GPT-5.4 catalog slug from `openai.gpt-5.4-cmb` to
`openai.gpt-5.4`.
- Align provider and catalog tests with the new URL and model ID.

## Test Plan

- Manual smoke test:

  ```shell
  target/debug/codex \
      -m openai.gpt-5.4 \
      -c 'model_provider="amazon-bedrock"' \
      -c 'model_providers.amazon-bedrock.aws.region="us-west-2"'
  ```

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

@@ -15,7 +15,7 @@ use codex_protocol::openai_models::WebSearchToolType;
 const GPT_OSS_CONTEXT_WINDOW: i64 = 128_000;
 const GPT_5_4_CONTEXT_WINDOW: i64 = 272_000;
 const GPT_5_4_MAX_CONTEXT_WINDOW: i64 = 1_000_000;
-const GPT_5_4_CMB_MODEL_ID: &str = "openai.gpt-5.4-cmb";
+const GPT_5_4_CMB_MODEL_ID: &str = "openai.gpt-5.4";
 
 pub(crate) fn static_model_catalog() -> ModelsResponse {
     ModelsResponse {

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

@@ -37,7 +37,7 @@ pub(super) fn region_from_config(aws: &ModelProviderAwsAuthInfo) -> Option<Strin
 
 pub(super) fn base_url(region: &str) -> Result<String> {
     if BEDROCK_MANTLE_SUPPORTED_REGIONS.contains(&region) {
-        Ok(format!("https://bedrock-mantle.{region}.api.aws/v1"))
+        Ok(format!("https://bedrock-mantle.{region}.api.aws/openai/v1"))
     } else {
         Err(CodexErr::Fatal(format!(
             "Amazon Bedrock Mantle does not support region `{region}`"
@@ -55,7 +55,7 @@ mod tests {
     fn base_url_uses_region_endpoint() {
         assert_eq!(
             base_url("ap-northeast-1").expect("supported region"),
-            "https://bedrock-mantle.ap-northeast-1.api.aws/v1"
+            "https://bedrock-mantle.ap-northeast-1.api.aws/openai/v1"
         );
     }
 

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

@@ -122,7 +122,7 @@ mod tests {
 
         assert_eq!(
             api_provider.base_url,
-            "https://bedrock-mantle.eu-central-1.api.aws/v1"
+            "https://bedrock-mantle.eu-central-1.api.aws/openai/v1"
         );
     }
 

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

@@ -461,7 +461,7 @@ mod tests {
         assert_eq!(
             model_ids,
             vec![
-                "openai.gpt-5.4-cmb",
+                "openai.gpt-5.4",
                 "openai.gpt-oss-120b",
                 "openai.gpt-oss-20b"
             ]
@@ -474,7 +474,7 @@ mod tests {
             .find(|preset| preset.is_default)
             .expect("Bedrock catalog should have a default model");
 
-        assert_eq!(default_model.model, "openai.gpt-5.4-cmb");
+        assert_eq!(default_model.model, "openai.gpt-5.4");
     }
 
     #[tokio::test]