Pattern Proposal: Adapter-Based Client Substitution

Summary

Provide interchangeable client implementations using a shared interface to allow seamless switching between live external dependencies and local mocks.

Candidate Pattern

• ID: adapter-based-client-substitution
• 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 client adapter wrapping the third-party LiteLLM library.
• src/cas_runner/llm/mock_client.py (MockLLMClient) - Deterministic mock client adapter enabling test harness and offline runs.

Scope Assessment

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

Rationale

• Intent: Decouple external provider communications from internal execution flow and enable deterministic offline unit testing.
• Context: The system depends on external LLM inference providers via litellm, but must also be able to run offline, during automated CI, or in unit tests.
• Force: External API calls are non-deterministic, network-dependent, and introduce cost
• Force: Testing pipeline execution without external credentials requires deterministic mocking

Traceability

Artifact source: proposed-patterns