0002-provider-abstraction-and-model-routing.md

ADR 0002: Provider Abstraction and Model Routing

• Status: accepted
• Date: 2026-02-13

Context

Agent must support multiple LLM vendors while keeping core execution logic provider-agnostic.

Decision

Introduce Agent::Providers with a single provider contract:

generate_code(model:, system_prompt:, user_prompt:, tool_schema:) -> String

Routing strategy:

• Default provider: Anthropic.
• Auto-route OpenAI-compatible models by prefix (gpt-, o1-, o3-, o4-, chatgpt-).
• Allow explicit provider: override.
• Lazily load provider gems only when instantiated.

Consequences

• Positive: core logic stays stable while providers evolve independently.
• Positive: easier testability via provider doubles.
• Tradeoff: routing rules require periodic updates as model naming conventions change.