Table not found in AddRuleToTopology

Question

The following code works as expected in an ArcGIS Notebook (2.9.x):

# variables
arcpy.env.workspace = r"\\foo\Staging\NG911.gdb\ESINET"
staging = r"\\foo\Staging\NG911.gdb\ESINET"
ng_pb = os.path.join(staging, "NG911_PB")
topology = os.path.join(staging, "ESI_topology")
fcs = arcpy.ListFeatureClasses()

# create topology
arcpy.management.CreateTopology(staging, "ESI_topology")
print('topology created')
for fc in fcs:
    arcpy.management.AddFeatureClassToTopology(topology, fc, 1,1)
    print(arcpy.GetMessages())

# rules for polygon layers
topoRules = ["Must Be Covered By Feature Class Of (Area-Area)", "Must Be Properly Inside 
(Point-Area)", "Must Be Inside (Line-Area)"]
boundaries = fcs[0:3]
sitepts = fcs[4]
centerline = fcs[5]

# add rules
for fc in boundaries:
    arcpy.management.AddRuleToTopology(topology, topoRules[0], fc, '', ng_pb, '')
    arcpy.management.AddRuleToTopology(topology, topoRules[0], ng_pb, '', fc, '')
    print(arcpy.GetMessages())

But when I run it as a standalone script in Python 3.7.x shell I get the following error:

Traceback (most recent call last):


File "C:\ESINET\Python\esinet_2.py", line 96, in <module>
    arcpy.management.AddRuleToTopology(topology, topoRules[0], fc, '', ng_pb, '')
File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\management.py", line 22746, in AddRuleToTopology
    raise e
File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\management.py", line 22743, in AddRuleToTopology
    retval = convertArcObjectToPythonObject(gp.AddRuleToTopology_management(*gp_fixargs((in_topology, rule_type, in_featureclass, subtype, in_featureclass2, subtype2), True)))
File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\geoprocessing\_base.py", line 512, in <lambda>
    return lambda *args: val(*gp_fixargs(args, True))
arcgisscripting.ExecuteError: ERROR 999999: Something unexpected caused the tool to fail. Contact Esri Technical Support (http://esriurl.com/support) to Report a Bug, and refer to the error help for potential solutions or workarounds.
The table was not found. [ESI_topology]
The table was not found. [ESI_topology]
Failed to execute (AddRuleToTopology).

I've tried a few different ways of declaring the ESI_topology table (full path rather than using os.join, plain text rather than a variable since my workspace is set to the Feature Dataset) but I'm really at a loss for why this isn't working outside of ArcGIS Pro. Error 999999 of course isn't helpful at all, so I'm hoping someone will recognize something out of place.