Continuation-based runtime callback invocation

Activity callbacks in a continuation-based runtime. At framework-definition time, a framework activity is authored. The framework activity may have an environmental logic portion the processes input or output parameters whose values will be supplied to and/or received from an activity callback. The framework activity also includes a callback invocation portion that, during execution time, will actually provide parameter value(s) to and/or receive parameter value(s) from the activity callback. The framework activity serves as a framework that operates with any activity callback that has one or more characteristics. Such activity callbacks may not even be defined at framework-definition time. Instead, the framework activity may be used multiple times in the same applications, or in different applications to thereby provide core framework functionality, while allowing application developers to plug in activity callbacks that meet the custom needs of the application.