In a multi-agent pipeline, a worker agent returns a tool result claiming it successfully executed a database schema migration. Before the supervisor proceeds to deploy the application code that depends on this schema change, what is the correct validation approach?

A is correct because in critical multi-agent pipelines, an agent's reported outcome should be independently verified before proceeding to dependent steps. Tool execution can succeed partially, report success despite side effects, or return stale cached data. Having the supervisor issue an independent verification query (confirming the schema change exists) converts an unverified claim into a verified state. For irreversible downstream actions like deployment, this validation gate is architecturally essential. B is wrong because agent-to-agent communication is not inherently reliable — worker agents can misinterpret tool results, tools can return false positives, and errors in complex pipelines are common. Blind trust violates defense-in-depth principles. C is wrong because running three independent migrations and voting creates database conflicts and race conditions — it is appropriate for read operations, not destructive write operations like schema migrations. D is wrong because relying on rollback as the primary validation strategy is reactive rather than preventive; failed deployments on top of a bad schema can cause cascading data corruption that rollback cannot fully reverse.