fix(grok): strip unsupported reasoning parameters for Composer

[JD13703202]

Summary

• remove unsupported reasoning parameters from Grok Composer Responses requests
• preserve reasoning configuration for Grok models that support it
• add regression coverage for Composer aliases and provider-prefixed model names

Problem

The Anthropic Messages to Responses conversion adds a default reasoning.effort value. grok-composer-2.5-fast does not support this parameter and rejects the request:

400 invalid-argument:
Model grok-composer-2.5-fast does not support parameter reasoningEffort.

This affects /v1/messages requests converted to /v1/responses, including Claude Code Composer side requests.

Fix

Before forwarding a Grok Responses request, remove:

• reasoning
• reasoning_effort
• reasoningEffort

when the effective upstream model is grok-composer-2.5-fast, composer-2.5, or a provider-prefixed equivalent.

Other Grok models retain their reasoning configuration.

Validation

• added regression coverage for the canonical model, alias, and provider-prefixed form
• added regression coverage confirming grok-4.5 preserves reasoning parameters
• git diff --check passed
• focused Go tests were not run locally because the installed Snap Go toolchain lacks the required cap_dac_override capability

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[JD13703202]

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