When allocating the workspace using exwsAllocate step, provide a unique workspace for each Pull Request. So the allocated workspace path on the disk shall be like: $physicalPathOnDisk/$jobName/$pullRequestNumber/$buildNumber

Additional details.

• The relative path is configurable within Build DSL
• [Nice2have]: Be able to specify path in the template. Maybe complicated, because for template we may need to resolve build environment variables
• Workspace cleanup should work properly with such workspaces
• Plugin should prevent workspace collisions (for example $physicalPathOnDisk/$jobName/A and $physicalPathOnDisk/$jobName/A/B)

Reference: https://github.com/martinda/external-workspace-manager/blob/master/README.md#advanced-usage-git-pull-request