As described in the source of gradle: The ID of a single build invocation.

Here, the term "build" is used to represent the overall invocation. For example, buildSrc shares the same build scope ID as the overall build. All composite participants also share the same build scope ID. That is, all “nested” builds (in terms of GradleLauncher etc.) share the same build ID.

This ID is, by definition, not persistent.