An instance is created at the start of a Gradle invocation and discarded at the end of that invocation.

The build session state also includes "cross session" state that is shared with any "nested" sessions that need to be created.
This only happens when the `GradleBuild` task is used. You can mostly ignore the distinction between "cross session" and "build session" state.

### Build tree state

"Build tree" is another name for the build definition.