Pattern Proposal: Swappable Provider Adapter

Summary

Isolates external client interfaces behind interchangeable client implementations, enabling mock substitution for tests and offline runs.

Candidate Pattern

• ID: swappable-provider-adapter
• Classification: architectural
• Maturity: established
• Type: implemented

Observed Signals

No specific signals listed.

Evidence

Supporting Evidence

• src/cas_runner/llm/litellm_client.py (LiteLLMClient) - Live external provider implementation.
• src/cas_runner/llm/mock_client.py (MockLLMClient) - Deterministic mock provider implementation for offline or test scenarios.

Scope Assessment

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

Rationale

• Intent: Decouple application services from concrete external API clients to facilitate offline development and unit testing.
• Context: External integrations (like LiteLLM) incur costs, latency, and require API keys that may not be present in CI environments.
• Force: Automated CI testing requires deterministic responses without network calls.
• Force: Production runtime requires real remote API invocation.

Traceability

Artifact source: proposed-patterns