User should be able to get positions of devices from the REST client.

[DiamondJoseph]

We expose the move stub, which takes a mapping of device to value to move them to. But we don't expose what type value should be per device, and for those devices with a JSONable value (which is probably only those that are Movable) we currently do not have any way of getting the location of those devices without running a count plan.

There should be a REST endpoint that can be called to:
If there is a running task, return 503: Server Busy
Otherwise:
Create a task to read either a selection or all of the Movable devices
Return those values as a JSON blob {"device_name": device_value}.

[callumforrester]

Yes, I've been wondering exactly what form this should take, and whether it should work while a plan is running...
On the one hand, making plans as atomic as possible is a good thing, on the other hand asynchronous monitoring would give feature parity with GDA

[DiamondJoseph]

Now that the RunEngine is in its own subprocess, can you call device.locate() while a plan is in progress?

[callumforrester]

Devices are also in the subprocess, see #371

[stan-dot]

what if the ophyd devices stream kafka events?