automated stop for PS-2 or PS-3 engine and restart to previous speed

If you drop voltage down to about 8,the engine will stall and remain in command. Stall voltage varies somewhat between engines. Some say this can damage the electronics so do it at your own risk. I made up a circuit for a guy who wanted to stop 2 trolleys at a crossover so they did not collide,he experienced no ill effects.  To drop voltage,you can use a string of bridge rectifiers or in some instances a separate transformer tap if they car separated with relay contacts to avoid paralleling the 8 volts with the 18 volt track circuit.

Dropping voltage with diodes is described here. Do not use a rheostat.

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In some cases you may have to install some diodes in the engine to raise stall voltage. Described here

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Crossover protection is described here. The stall voltage can be left on the unused NO contacts.

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Dale H

Does Fwd/Fwd mean Conventional locked-direction mode? Or is this DCS Command mode?

Do you have a spare transformer/controller lying around or a source of fixed AC voltage such as accessory power?  It might be easier to derive a suitable voltage from a separate source than from mainline track voltage.