ANTHROPIC_DEFAULT_OPUS_MODEL env var not honored when selecting Opus 4.5 from /model list

Bug Description

When specifying the ANTHROPIC_DEFAULT_OPUS_MODEL environment variable pointing to Claude Opus 4.5 (via AWS Bedrock), selecting "Opus 4.5" from the /model list does not honor the environment variable. Instead, it results in an AWS Bedrock error.

However, when selecting "Opus 4.1" from the /model list, Claude Opus 4.5 is correctly used (as specified in the env var).

Steps to Reproduce

1. Set ANTHROPIC_DEFAULT_OPUS_MODEL environment variable to a Claude Opus 4.5 Bedrock inference profile ARN
2. Start Claude Code
3. Run /model and select "Opus 4.5"
4. Observe: AWS Bedrock error occurs (env var not honored)

Expected Behavior

Selecting "Opus 4.5" from the /model list should use the model specified in ANTHROPIC_DEFAULT_OPUS_MODEL environment variable.

Actual Behavior

• Selecting "Opus 4.5" ignores the ANTHROPIC_DEFAULT_OPUS_MODEL env var and causes an error
• Selecting "Opus 4.1" correctly uses the Opus 4.5 model specified in the env var

Environment

• Using AWS Bedrock as the model provider
• ANTHROPIC_DEFAULT_OPUS_MODEL set to Opus 4.5 inference profile ARN