Introducing new entry-points that can be used from both Driver and Frontend clients, using an intermediary new type: `DetailedMessagePayload`, when needed.
Starting at a crude -1000, each invocation primary input will get its own unique quasi-Pid.
Invocations with only one primary (non-batch) will get a real OS Pid.
The selection of the constant starting point matches what the driver does when outputting its parseable output.
