Which annotation exposes an Apex class as a RESTful web service?

Universal Containers implemented a private sharing model for the Account object. A custom Account search tool was developed with Apex to help sales representatives find accounts that match multiple criteria they specify. Since its release, users of the tool report they can see Accounts they do not own. What should the developer use to enforce sharing permission for the currently logged-in user while using the custom search tool?

What are two ways for a developer to execute tests in an org?

When using SalesforceDX, what does a developer need to enable to create and manage scratch orgs?

A workflow updates the value of a custom field for an existing Account.
How can a developer access the updated custom field value from a trigger?