[BUG] Bedrock: session title generation fails silently — output_config rejected with 'Extra inputs are not permitted'

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Environment

• Claude Code version: 2.1.138
• Backend: AWS Bedrock
• Model: us.anthropic.claude-sonnet-4-6 (main), Haiku used for title generation
• Platform: WSL2 on Windows, Linux
• Environment variables:

``
CLAUDE_CODE_USE_BEDROCK=1
AWS_PROFILE=<profile with Bedrock access>
``

Describe the bug

Session title generation silently fails on Bedrock. Claude Code sends output_config (with json_schema format) in the title generation request to Haiku, but Bedrock rejects this field:

ValidationException: output: Extra inputs are not permitted

The terminal tab title stays as "⠂ Claude Code" permanently instead of being updated with an auto-generated session name.

This is the same root cause as #52312 (fixed for Vertex AI in v2.1.122), but the fix was not applied to Bedrock. On v2.1.138, Bedrock still receives and rejects output_config.

Reproduction confirmation

I confirmed Haiku is accessible on the same Bedrock profile (direct invocation works), and that the output_config field is what causes the rejection:

# This works:
echo '{"anthropic_version":"bedrock-2023-05-31","max_tokens":50,"messages":[{"role":"user","content":"Say hi"}]}' | \
aws bedrock-runtime invoke-model --model-id us.anthropic.claude-haiku-4-5-20251001-v1:0 ...
# ✓ Success

# This fails (adding output_config):
echo '{"anthropic_version":"bedrock-2023-05-31","max_tokens":100,...,"output_config":{"format":{"type":"json_schema","schema":{...}}}}' | \
aws bedrock-runtime invoke-model --model-id us.anthropic.claude-haiku-4-5-20251001-v1:0 ...
# ✗ ValidationException: output: Extra inputs are not permitted

Actual behavior

Title generation fails silently. The pane title remains "⠂ Claude Code" for the entire session. No error is shown to the user. /rename updates the internal session label but not the terminal title (#55197).

What Should Happen?

When CLAUDE_CODE_USE_BEDROCK=1 is set, Claude Code should not include output_config in requests sent to Bedrock (same fix as was applied for Vertex in v2.1.122). JSON output for title generation should be enforced via prompt instructions instead, or use a Bedrock-compatible structured output format.

Error Messages/Logs

The error is swallowed internally. Confirmed via direct API testing:

ValidationException: output: Extra inputs are not permitted

Steps to Reproduce

1. Set CLAUDE_CODE_USE_BEDROCK=1 and configure a valid AWS profile with Bedrock access
2. Start a new claude session
3. Send any message
4. Observe the terminal tab title — it stays as "⠂ Claude Code" and never updates

Claude Model

claude-sonnet-4-6 (Haiku for title generation)

Is this a regression?

Yes — this is the Bedrock equivalent of #52312, which was fixed for Vertex AI in v2.1.122 but not for Bedrock.

Last Working Version

Never worked on Bedrock (structured output has never been supported on Bedrock's InvokeModel API).

Claude Code Version

2.1.138

Platform

Amazon Bedrock

Operating System

Linux (WSL2)

Terminal/Shell

Windows Terminal + tmux + zsh

Additional Information

Related issues:

• #52312 — Same bug on Vertex AI (fixed in v2.1.122)
• #55197 — /rename doesn't update terminal title (separate but compounding issue)
• #54224 — PostToolUse hooks also hit this on Vertex