Which two key mechanisms turn an ordinary Apex class into an invocable action?

For an Apex class to be recognized as an invocable action within Salesforce, it must incorporate specific mechanisms that enable it to be invoked by other processes, such as Process Builder or Flow.

The correct answer emphasizes the addition of the InvocableMethod interface to the class, which is essential for marking methods as invocable actions. This interface allows the class to expose methods that can be called from within flows or Process Builder. Additionally, it is crucial to define input and output variables to ensure that the invocable method can receive data appropriately and return results after execution. This structured input-output configuration is what facilitates communication between the invoked action and the process that calls it.

This approach provides a seamless integration of Apex processes with Salesforce's declarative tools, creating a much more flexible automation environment. Thus, having the InvocableMethod interface along with well-defined input and output parameters is what distinguishes an ordinary Apex class as an invocable action.