Add a feature flag for Code Mode tool description ordering

[copyberry]

Add a feature flag for Code Mode tool description ordering

What changed

Register code_mode_tool_description_first as an under-development feature, disabled by default, for placing tool descriptions before namespace descriptions in Code Mode. Add the boolean option to the configuration schema.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	🔄 Running since 2026-10-07T13:25:38.675085Z	30c13ee	PR opened

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