Amazon Bedrock Mantle provider uses incorrect /openai/v1 endpoint path

What version of Codex CLI is running?

Built locally from the current openai/codex mainline with a one-commit fix applied.

What issue are you seeing?

The built-in amazon-bedrock provider points Bedrock Mantle requests at:

https://bedrock-mantle.<region>.api.aws/openai/v1

but AWS Bedrock Mantle exposes its OpenAI-compatible APIs directly under:

https://bedrock-mantle.<region>.api.aws/v1

As a result, Codex Responses requests should go to /v1/responses, not /openai/v1/responses.

Root cause

This appears easy to confuse with the separate Bedrock Runtime OpenAI-compatible Chat Completions endpoint, which AWS documents as:

https://bedrock-runtime.<region>.amazonaws.com/openai/v1

Bedrock Mantle is a different endpoint family and uses /v1.

References:

• https://docs.aws.amazon.com/bedrock/latest/userguide/bedrock-mantle.html
• https://docs.aws.amazon.com/bedrock/latest/userguide/model-parameters-openai.html
• https://docs.aws.amazon.com/bedrock/latest/userguide/endpoints.html

Verified fix

I prepared a local fix:

• Branch: toyamarinyon/codex:fix-bedrock-mantle-responses-url
• Commit: 1b5b98213e07d34dddd25e35d9d0129e8e062455

I could not open a PR because this repository currently limits PR creation to collaborators.

Verification

Unit tests run:

cargo fmt
cargo test -p codex-model-provider-info test_create_amazon_bedrock_provider
cargo test -p codex-model-provider base_url_uses_region_endpoint
MACOSX_DEPLOYMENT_TARGET=15.0 CXXFLAGS="..." cargo test -p codex-tui status_model_provider_uses_bedrock_runtime_base_url

I also verified locally with the built artifact:

target/debug/codex \
  -c 'model_provider="amazon-bedrock"' \
  -c 'model="openai.gpt-oss-120b"' \
  -c 'model_providers.amazon-bedrock.aws.profile="codex-bedrock"' \
  -c 'model_providers.amazon-bedrock.aws.region="ap-northeast-1"' \
  exec 'Say hello in one sentence.'

This succeeded through the amazon-bedrock provider and reached:

https://bedrock-mantle.ap-northeast-1.api.aws/v1/responses

Expected behavior

The built-in Amazon Bedrock provider should use:

https://bedrock-mantle.<region>.api.aws/v1

for Bedrock Mantle, so Responses requests are sent to /v1/responses.

Actual behavior

The current default and generated region-specific URLs include /openai/v1, which belongs to the Bedrock Runtime Chat Completions compatibility path, not Bedrock Mantle.