Organizations that own web services participating in a workflow composition may evolve their components independently. Service coordination can fail when previously legal messages between independently changing, distributed components become illegal because their respective workflow models are no longer synchronized. This paper presents an intelligent-agent framework that wraps a web service in a conversation layer and a simple workflow-adaptation function. The conversation layer implements protocols and consults globally shared, declarative policy specifications to resolve interaction failures. The framework allows agents to resolves various model mismatches that cause interaction errors, including changes to required preconditions, partners, and expected message ordering. Implications of this distributed approach to web service coordination are also discussed.