Task tool model:'opus' resolves to stale claude-opus-4-1 on Bedrock EU region

Bug Description

When spawning subagents via the Task tool with model: "opus", the model alias resolves to eu.anthropic.claude-opus-4-1-20250805-v1:0 instead of the current claude-opus-4-6 model. This causes a 400 API error on AWS Bedrock in the EU region, as that model identifier is invalid/unavailable.

Environment

• Claude Code version: Latest (as of 2026-02-28)
• Backend: AWS Bedrock (CLAUDE_CODE_USE_BEDROCK=1)
• Region: eu-west-1
• Parent session model: eu.anthropic.claude-opus-4-6-v1 (set via /model and settings.json)
• OS: macOS (Darwin 25.3.0)

Steps to Reproduce

1. Configure Claude Code to use Bedrock in EU region
2. Set model to eu.anthropic.claude-opus-4-6-v1 via /model
3. Spawn a subagent using the Task tool with model: "opus":

``
Task({
subagent_type: "general-purpose",
model: "opus",
prompt: "Do something",
run_in_background: true
})
``

1. The subagent fails immediately with:

``
API Error (eu.anthropic.claude-opus-4-1-20250805-v1:0): 400 The provided model identifier is invalid.
Run /model to pick a different model.
``

Expected Behavior

model: "opus" should resolve to the same model as the parent session (eu.anthropic.claude-opus-4-6-v1), or at minimum to the latest available Opus model in the configured region.

Actual Behavior

• model: "opus" resolves to the stale eu.anthropic.claude-opus-4-1-20250805-v1:0 identifier
• The subagent cannot make any API calls and enters an infinite idle loop
• The subagent becomes unresponsive to shutdown requests (cannot be terminated gracefully)
• TeamDelete is blocked because the zombie agents remain "active"

Impact

• Subagents using model: "opus" are completely non-functional on Bedrock EU
• Zombie agents that can't be shut down block team cleanup
• No workaround exists other than avoiding model: "opus" entirely (using model: "sonnet" or omitting the parameter works fine)

Workaround

• Don't pass model: "opus" to the Task tool
• Either omit the model parameter (inherits parent session model) or use model: "sonnet"

Additional Notes

• model: "sonnet" resolves correctly and works fine
• model: "haiku" was not tested but may have the same issue
• The settings.json model field is correctly set to eu.anthropic.claude-opus-4-6-v1 — the issue is in the internal alias mapping for the Task tool's model enum, not in user configuration
• The model alias table appears to be hardcoded and not configurable via settings or environment variables