[FEATURE]: /compact should be configurable to use OpenAI Responses API 'compaction'

[ddbaron]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

For OpenAI models using Responses API, there is a /compact API:
https://cookbook.openai.com/examples/gpt-5/gpt-5-1-codex-max_prompting_guide#compaction
https://platform.openai.com/docs/api-reference/responses/compact

OC should allow configurable use of this API when utilizing the OC /compact command so the user can either use the OC compact (default) or configure their model to use the OpenAI compact instead.

[github-actions]

This issue relates to several existing discussions around OpenAI Responses API configuration. While not direct duplicates, you may want to check these related issues:

• Model in @ai-sdk/openai sdk fails on the 2nd request #5104: Model configuration with Responses API parameters (store, include, reasoningEffort)
• Using GPT 5.1 Codex via OpenAI fails on the 2nd request #4445: GPT 5.1 Codex requiring model-specific Responses API configuration
• [FEATURE] Sliding window context management for long-running sessions #4659: Alternative compaction strategies for context management

These issues show similar requests for configurable API-specific features and behaviors. Your feature request for a configurable /compact command aligns with this broader need for model/provider-specific configurability in OpenCode.