Summary

Add support for all three OpenAI API paths in openab-agent, matching Pi coding agent's multi-provider architecture.

Checklist

• openai — Responses API → api.openai.com/v1/responses — Auth: OPENAI_API_KEY
• openai-codex — Codex Responses → chatgpt.com/backend-api/codex/responses — Auth: OAuth token (subscription)
• Third-party — Chat Completions → Various /v1/chat/completions — Auth: Various API keys

Current State

Only openai-codex is implemented today.

Why

• Users with OPENAI_API_KEY (pay-per-token) cannot use openab-agent without a ChatGPT subscription
• The Responses API (/v1/responses) is OpenAI's latest for their own models — reasoning, structured output, tool use
• Chat Completions (/v1/chat/completions) enables third-party OpenAI-compatible services (Groq, Cerebras, DeepSeek, etc.)
• Pi supports all three paths

Prior Art

• Pi openai-responses: https://github.com/earendil-works/pi/blob/main/packages/ai/src/providers/openai-responses.ts
• Pi openai-codex-responses: https://github.com/earendil-works/pi/blob/main/packages/ai/src/providers/openai-codex-responses.ts
• Pi openai-completions: https://github.com/earendil-works/pi/blob/main/packages/ai/src/providers/openai-completions.ts

Discussion

Thread: 1513356640072499221