A SaaS vendor runs a Claude assistant for 30 enterprise tenants. Each tenant has a hand-edited copy of the system prompt. A policy correction had to be applied 30 times, four copies were missed, and one tenant's copy now contradicts the base rules. What is the best long-term fix?

Answer: D — Render prompts from a versioned base template plus small tenant modules, gated by a regression eval

(d) is right: composing a base template with scoped modules removes the duplication, version control makes changes reviewable, and the regression eval catches breakage before release. (a) keeps the forks and relies on manual diffing. (b) creates a contradictory monolith that every tenant sees. (c) multiplies uncontrolled edits and loses the shared policy baseline.