System rules live in the harness
Tone, forbidden actions, and output shape belong in a versioned system prompt. User messages carry the task. InferentCloud stores prompts next to tools and evals so a change is reviewable.
Structured output
Ask Claude for schema-bound JSON, then validate before any tool write. Failed validation retries with a repair instruction. Unchecked free text is not an API.
Evals over vibes
Golden inputs in CI catch prompt drift. Track business metrics (resolution, cycle time) as well as model scores.
Summary
Prompt engineering for an agency is harness engineering: instructions, schemas, retries, and evals around Claude.
