[BUG] Cowork on Bedrock: subagent spawner hardcodes wrong model ID (missing us.anthropic. prefix and -v1:0 suffix)

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?

Subagent spawner sends: claude-haiku-4-5-20251001
Bedrock requires: us.anthropic.claude-haiku-4-5-20251001-v1:0

Error: API Error (claude-haiku-4-5-20251001): 400
The provided model identifier is invalid.

The Cowork subagent spawning path does not apply the same
model ID prefix/suffix translation used by main session inference.

What Should Happen?

Expected Behavior

Cowork subagent spawner should apply the same model ID
prefix/suffix translation used by the main session
inference path.

Error Messages/Logs

API Error (claude-haiku-4-5-20251001): 400 The provided model identifier is invalid.

Steps to Reproduce

1. Configure Claude Desktop with Cowork 3P Bedrock

(inferenceBedrockProfile, us-east-1)

1. Start a new Cowork conversation
2. Ask Claude to read two files simultaneously using parallel agents
3. Observe subagent launch failure

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Code CLI: 2.1.116 Claude Desktop (Cowork): 1.5354.0 (9a9e3d) 2026-04-29T01:14:34.000Z

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

Other

Additional Information

Attempted workarounds — all failed:

1. inferenceModels plist with full ID
2. CLAUDE_CODE_SUBAGENT_MODEL via launchctl setenv
3. ANTHROPIC_DEFAULT_HAIKU_MODEL via launchctl setenv
4. ANTHROPIC_SMALL_FAST_MODEL via launchctl setenv
5. modelOverrides in plist

Workaround: Parallel tool calls within single session work
but full subagent delegation is broken.

Related: #21235 (fixed for CLI, not Cowork), #25193 (locked)