Custom Plugin Development for Vault Zero Trust Integration

Act as a Senior Golang Security Developer. Provide a comprehensive, highly technical architectural framework for developing a bespoke, compiled HashiCorp Vault [PLUGIN_TYPE] plugin (e.g., a custom Secrets Engine or Auth Method) written strictly in Golang. The plugin's sole purpose is to securely interface with an archaic or proprietary [EXTERNAL_SYSTEM] (e.g., a mainframe banking API). The plugin codebase must natively support and enforce absolute Zero Trust principles by executing a rigid [AUTH_MECHANISM] verification before ever returning a byte of data. Explicitly outline the required Golang `logical.Backend` and `logical.Path` struct architectures, detail the precise cryptographic logic required for securely handling the `context.Context` payload during high-concurrency requests, and provide the exact SHA-256 checksum registration process required to safely mount and execute the compiled plugin binary within a live, production Vault server.