Feature: Phase 5 - Provider Layer with LLM and Retriever Adapters

[himanshu231204]

Summary

Implement Phase 5 (Providers) for OpenAgent Eval - a complete provider layer with LLM and Retriever interfaces, adapters for 6 LLM providers and 1 retriever, and comprehensive unit tests.

Motivation

Phase 5 is required to enable the evaluation pipeline to interact with external LLM services and vector databases. The provider layer follows the adapter pattern, allowing the framework to be framework-agnostic while supporting multiple LLM providers and retrieval backends.

Files Modified

New Files

• openagent_eval/providers/base/llm.py - LLMProvider ABC with async generate() and get_token_count()
• openagent_eval/providers/base/retriever.py - Retriever ABC with async retrieve()
• openagent_eval/providers/models.py - LLMResponse, Document, TokenUsage Pydantic v2 models
• openagent_eval/providers/llm/openai.py - OpenAI adapter with tiktoken
• openagent_eval/providers/llm/gemini.py - Gemini adapter with google-genai SDK
• openagent_eval/providers/llm/anthropic.py - Anthropic adapter with anthropic SDK
• openagent_eval/providers/llm/groq.py - Groq adapter with groq SDK
• openagent_eval/providers/llm/openrouter.py - OpenRouter adapter with httpx
• openagent_eval/providers/llm/ollama.py - Ollama adapter with httpx
• openagent_eval/providers/retrievers/chroma.py - ChromaRetriever with chromadb
• 8 test files under ests/unit/test_providers/

Modified Files

• openagent_eval/providers/init.py - Added exports
• openagent_eval/providers/base/init.py - Added exports
• openagent_eval/providers/llm/init.py - Added all LLM provider exports
• openagent_eval/providers/retrievers/init.py - Added ChromaRetriever export

Architectural Decisions

1. Async-first interface - All provider methods are async for parallel evaluation (per D006)
2. Adapter pattern - LLMProvider and Retriever are outbound ports, adapters implement them (per AGENT.md)
3. Dependency injection - All external dependencies injected via constructor
4. Pydantic v2 models - Immutable models with field validators for type safety
5. Token counting - All LLM providers implement get_token_count() for cost tracking

Breaking Changes

None - this is a new module addition.

Testing

• 138 new unit tests (all passing)
• All external dependencies mocked (no real API calls)
• Both success and error paths tested
• ABCs verified to be non-instantiable
• Model validation tests for all Pydantic models

Remaining TODOs

None - Phase 5 is complete.

Assumptions & Limitations

• OpenRouter uses simple whitespace-based token estimation (no tiktoken)
• Ollama token tracking uses API response metadata
• All providers require API keys via constructor or environment variables

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