feat: add OpenAI API integration support

[xuzhongpeng]

Add comprehensive OpenAI API adapter to support OpenAI-compatible API endpoints, enabling users to use OpenAI models alongside Claude models.

Changes:

• Add OpenAI API adapter with streaming support and tool calling
• Add OpenAI integration documentation with usage examples
• Update model configuration system to support OpenAI models
• Enhance authentication flow to handle OpenAI API keys
• Add model provider detection and routing logic

Closes #48

Summary by CodeRabbit

• New Features

  • Added OpenAI API compatibility mode, allowing use of OpenAI-compatible providers through environment variable configuration without code changes.
  • Support for multiple providers including DeepSeek, Azure OpenAI, and advanced models (o1/o3).

• Documentation

  • Added comprehensive configuration guide for OpenAI API mode, covering both JSON and command-line setup across all platforms.

• Improvements

  • Enhanced message normalization and null-safety handling.

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

This PR implements OpenAI-compatible API mode support, allowing users to configure and use OpenAI API endpoints instead of Anthropic's. It introduces environment variable configuration, an adapter translating Anthropic message format to OpenAI, model identifier mappings, and comprehensive documentation for multi-platform setup.

Changes

Cohort / File(s)	Summary
Documentation & Setup README.md, docs/features/openai.mdx, package.json	Added README checklist entry and comprehensive documentation for OpenAI mode configuration via ~/.claude/settings.json or shell environment variables (macOS/Linux/Windows), with examples for DeepSeek, Azure OpenAI, and large output models. Added openai ^6.0.0 SDK dependency.
Core API Integration src/services/api/client.ts, src/services/api/openaiAdapter.ts	Updated client factory to conditionally import and return OpenAI adapter when CLAUDE_CODE_USE_OPENAI is set. New adapter file implements Anthropic-compatible API surface by translating message formats, tool schemas, streaming deltas, and stop-reason mappings between OpenAI Chat Completions and Anthropic message protocols.
Model Configuration src/utils/model/configs.ts, src/utils/model/deprecation.ts, src/utils/model/providers.ts	Added OpenAI model identifier field (e.g., openai: 'claude-3-5-sonnet') to 11 model config constants; added deprecation tracking for OpenAI provider; extended APIProvider type union to include 'openai' and added detection logic in getAPIProvider().
Utility Functions src/services/api/claude.ts, src/utils/auth.ts, src/utils/messages.ts	Updated max output token resolution to read from OPENAI_MAX_TOKENS when OpenAI mode is active; short-circuit authentication when OpenAI API key is present; added defensive null/undefined guard in message processing and fallback for unrecognized message types.

Sequence Diagram

sequenceDiagram
    actor User
    participant CodeClient as Code Client<br/>(CLAUDE_CODE_USE_OPENAI=true)
    participant Adapter as OpenAI Adapter
    participant OpenAI as OpenAI API

    User->>CodeClient: Call message creation
    CodeClient->>CodeClient: Check CLAUDE_CODE_USE_OPENAI env
    CodeClient->>Adapter: Instantiate adapter with<br/>apiKey & baseURL
    
    CodeClient->>Adapter: createMessage(messages, tools, etc)
    Adapter->>Adapter: Convert Anthropic message<br/>format to OpenAI format
    Adapter->>Adapter: Map tool schemas &<br/>system prompts
    
    Adapter->>OpenAI: POST /chat/completions<br/>(with stream or non-stream)
    OpenAI-->>Adapter: Response deltas/completion
    
    Adapter->>Adapter: Convert OpenAI response<br/>to Anthropic message
    Adapter->>Adapter: Map stop reasons &<br/>assemble content blocks
    Adapter-->>CodeClient: Anthropic-compatible<br/>message object
    CodeClient-->>User: Processed result

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related PRs

• Feature/computer use/mac support #108: Both implement OpenAI compatibility layer using CLAUDE_CODE_USE_OPENAI gating and OpenAI-backed adapter in src/services/api/.
• 支持 OpenAI Chat 兼容协议 #99: Directly related as both add complete OpenAI provider integration with adapter, model mappings, provider enum, and documentation.

Suggested reviewers

• KonghaYao

Poem

🐰 A rabbit bounces through code so neat,
OpenAI doors now open sweet!
From Anthropic's path to broader ways,
New adapters bridge through API maze.
Configuration dances—settings dance too,
Multi-platform magic, fresh and new! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 38.89% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the main change: adding OpenAI API integration support to the project.
Linked Issues check	✅ Passed	The PR successfully implements the core requirement from issue #48: enabling support for non-Anthropic model providers via API key integration, specifically with OpenAI-compatible APIs.
Out of Scope Changes check	✅ Passed	All changes are directly related to the OpenAI API integration feature. Minor defensive improvements (null guards, default cases) are reasonable quality-of-life enhancements supporting the feature's robustness.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

⚔️ Resolve merge conflicts

• Resolve merge conflict in branch feat/support-openai-api

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[xuzhongpeng]

前天提交了一半忘提pr了，看到最新代码以及已经更新该功能了，快得离谱，现关闭pr