The job execution engine is driven by Hangfire. It's a job library for .NET that provides the ability to schedule jobs, retry jobs and scale horizontally with multiple agents. Eventually, UA will take more advantage of the features of Hangfire.
Jobs in UA are run in an out-of-process PowerShell host. Depending on the version of PowerShell that is run, either PowerShell.exe or Pwsh.exe will be run. A custom PowerShell host is loaded into the PowerShell process to listen for output, input requests and to provide the ability to interact with the host from the job engine.
Using gRPC, the job engine can communicate between the job scheduling process and the independent PowerShell hosts. By keeping the processes isolated, they will not conflict with each other.