Add an opt-in feature for subagent model context defaults

[copyberry]

Add an opt-in feature for subagent model context defaults

What changed

Add the disabled-by-default subagent_default_context_limits feature and expose it in the configuration schema. When enabled, shared configuration for spawning and resuming subagents clears inherited model_context_window and model_auto_compact_token_limit overrides so subagents use their model's default context window and auto-compaction threshold.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	🔄 Running since 2026-10-09T17:49:02.180307Z	3e84e1c	PR opened

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