Recursive purge is not recursive

Invoking DurableTaskClient.PurgeInstanceAsync with PurgeInstanceOptions.Recursive = true does not result in sub-orchestrations being purged. The documentation for this method states that sub-orchestrations should be purged when this flag is set.

Example:

var purgeInstanceOptions = new PurgeInstanceOptions
{
    Recursive = true
};

await client.PurgeInstanceAsync("my_instance_id", purgeInstanceOptions);

with rows in the Instances table that have ParentInstanceID=my_instance_id (in addition to the required InstanceID=my_instance_id row that has a RuntimeStatus of Completed, Terminated, or Failed), executes the following SQL:

declare @p1 dt.InstanceIDs
insert into @p1 values('my_instance_id')

exec dt.PurgeInstanceStateByID @InstanceIDs=@p1

(Stored procedure PurgeInstanceStateByID only uses the provided InstanceIDs - it does not perform a recursive CTE.)

Start at DurableTaskClient.PurgeInstanceAsync and PurgeInstanceOptions. Inspect how the recursive instance ID set is passed to dt.PurgeInstanceStateByID, using the Instances rows and ParentInstanceID example as the reproduction. Done means purging a completed, terminated, or failed parent also removes its sub-orchestrations.