feat: finalize encryption and voting provider contracts

docs/DEPLOYMENT_OPERATOR_GUIDE.md

@@ -36,7 +36,7 @@ set +a
 | Setting | Required outside dev | Purpose |
 | --- | --- | --- |
 | `APP_ENV` | yes | Runtime profile. Use `prod`, `staging`, or a deployment-specific value outside local development. |
-| `MASTER_KEY_B64` | yes | Fernet key or base64 encoded 32-byte key used for encrypted module secrets. Rotate through an explicit operator plan. |
+| `MASTER_KEY_B64` | yes | Fernet key or base64 encoded 32-byte deployment root used for encrypted module secrets and, when enabled, the Encryption module's local server-envelope provider. Rotate only through an explicit provider-aware migration plan. |
 | `DATABASE_URL` | yes | SQLAlchemy database URL for core and installed modules. SQLite is supported for dev/small installs; PostgreSQL is the preferred production target. |
 | `ENABLED_MODULES` | yes | Comma-separated startup module set. Keep `tenancy,access` enabled; keep `admin` enabled for operator UI. |
 
@@ -485,7 +485,7 @@ checks, catalog trust, signing, keyring, replay, and license operation.
 ## Operator Checklist
 
 - Runtime secrets are injected outside git.
-- `MASTER_KEY_B64` is set and backed up securely.
+- `MASTER_KEY_B64` is set and backed up securely; restores of locally encrypted content fail closed without the exact matching key.
 - Database backup and restore commands are tested.
 - File/object storage is durable and backed up.
 - `CORS_ORIGINS` and cookie settings match the deployed WebUI origin.