WorkflowHostAgent was initially implemented before Checkpointing was available. This meant that in order to support resuming, the WorkflowHostAgent needed to keep the runs around, which broke it when stricter rules about concurrent sharing of workflows during execution were introduced.
This change updates the hosting logic to release the underlying StreamingRun when the RunStreamingAsync or RunAsync are invoked, in favour of keeping the checkpointing information in the WorkflowThread to enable resumption.