Implementing Vault Transit Engine for Data-at-Rest Encryption

Act as a Cryptography Expert and Backend Developer. Architect and implement an 'Encryption-as-a-Service' (EaaS) perimeter utilizing HashiCorp Vault’s highly performant Transit Secrets Engine. You must provide a flawless, production-ready [APPLICATION_LANGUAGE] (e.g., Java, Go, Node.js) implementation that completely offloads all heavy cryptographic encoding and decoding operations directly to Vault's REST API utilizing the strict [ENCRYPTION_ALGORITHM] (e.g., `aes256-gcm96`). Define a merciless, automated [ROTATION_POLICY] for the underlying Transit encryption keys (e.g., auto-rotating every 30 days). Most critically, provide a deeply technical explanation detailing exactly how to configure and utilize 'Convergent Encryption' within the Transit engine to allow the application database to perform encrypted-data deduplication and exact-match querying without ever exposing the plaintext payload to the database layer, satisfying absolute Zero Trust requirements.