Pattern Proposal: Polymorphic Client Adapter

Summary

Provide interchangeable production and mock implementations conforming to a shared client interface.

Candidate Pattern

• ID: polymorphic-client-adapter
• Classification: architectural
• Maturity: strategic_direction
• Type: emerging

Observed Signals

No specific signals listed.

Evidence

Supporting Evidence

• src/cas_runner/llm/litellm_client.py (LiteLLMClient) - Production implementation interfacing with litellm library.
• src/cas_runner/llm/mock_client.py (MockLLMClient) - Mock test double implementing the client contract for offline/deterministic runs.

Scope Assessment

• Evidence Strength: high
• Confidence: high
• Applies to: ideas-to-life-cas

Rationale

• Intent: Enable offline testing, deterministic CI runs, and swappable backends without coupling core workflows to live external network services.
• Context: System relies on external model providers via LiteLLM during normal runs, but CI/test pipelines need deterministic execution without external API keys.
• Force: Network-dependent client invocations make automated test suites flaky and expensive.
• Force: Business logic should not know whether it is communicating with a live model or a mock provider.

Traceability

Artifact source: proposed-patterns