`bp.grid_scan` *snake_axes* arg does not accept a list of device names

[canismarko]

I'm trying to add the following plan to the queueserver:

{
    'item_type': 'plan', 
    'name': 'grid_scan', 
    'args': [
        ['Ipreslit_v1', 'I0', 'ge_13element', 'Ipreslit_v2', 'Ipreslit_h2', 'Ipreslit_h1', 'Iref', 'It'], 
        'aerotech.vertical', 40475.0, 40725.0, 51,
        'aerotech.horizontal', 23636.0, 23886.0, 51
    ], 
    'kwargs': {
        'snake_axes': ['aerotech.horizontal'],
        'md': {
            'sample_name': 'Calibration target', 
            'scan_name': 'test fly grid scan', 
            'purpose': 'commissioning', 
            'notes': 'Check if we can launch fly scans from Firefly'
        }
    }
}

According to the docstring for this plan:

snake_axes: boolean or iterable, optional
which axes should be snaked, either False (do not snake any axes),
True (snake all axes) or a list of axes to snake. "Snaking" an axis
is defined as following snake-like, winding trajectory instead of a
simple left-to-right trajectory. The elements of the list are motors
that are listed in args. The list must not contain the slowest
(first) motor, since it can't be snaked.

Since "aerotech.horizontal" is listed in args, I would expect that the plan I listed above would snake along that axis. However, I when I try to run this plan, I get the following:

If I do the equivalent scan directly in a REPL where snake_axes is a list of the actual motors, then the scan proceeds as expected. If I replace ['aerotech.horizontal'] with True on the queueserver, it also works correctly.

I suspect the snake_axes argument is not being transformed back into the device object by the queueserver?

[dmgav]

I need to double check, but I suspect that if the annotation for snake_axes parameter is changed to Optional[Union[Iterable[Movable], bool], then the motor names will be converted to objects.

[canismarko]

Thanks @dmgav. I think that makes sense. That would make this an issue with bluesky then, right?