Currently I see no way to determine if a build was triggered by a commit to the PR target branch versus a commit to the base branch.

In both cases the reason for trigger was "Branch Indexing".

The only work around I found was to pull both branches and compare the change sets to it - which is tedious and requires a heavy worker to run since I need repos.

Proposed - either add a new trigger cause to expand upon Branch Indexing or create an environment variable that states why the build is being run.