Tracking recent rigify changes? Apparently they decided to change all the pole toggle functions.
They seem to work / require a different signature then previous version - this has broken many plugins - (Why on earth would you ever change the order of a function signature on something that you need to be backwards compatible?)

Is there any way to track down these source changes to identify the new function signature requirements?
Basically, any test I throw into the console shoots out a JSONDecodeError because of one of the values either being empty.

No, the function described within Autocomplete is either Not complete, or inaccurate and produces errors.
Also note that it is Instanced on a per-rig basis through the rig_ui.py
However it doesn't appear (at a cursory overlook) to contain the specific function itself.
So, I ended up modifying limb_rigs.py @ line 1014 with the following prints

print("Dir Result", dir(self.properties))
print("ctrl_bones",self.properties.ctrl_bones)
print("extra_ctrls",self.properties.extra_ctrls)
print("fk_bones",self.properties.fk_bones)
print("ik_bones",self.properties.ik_bones)
print("pole_prop",self.properties.pole_prop)
print("prop_bone",self.properties.prop_bone)
print("use_pole",self.properties.use_pole)


this outputs the results of a signature enough to pinpoint any new bones and variables that need passing.

It seems to me that the current implementation of the function suffers from a bug when variables are left empty as they should be.

fk_bones is always empty. but a value is required for calling the function because of it's type.
As a result you need a call of this sort

bpy.ops.pose.rigify_limb_toggle_pole_wlnrc42c2a6335e5(
prop_bone="upper_arm_parent.L", 
pole_prop="pole_vector", 
fk_bones='[""]',
ik_bones='["upper_arm_ik.L", "MCH-forearm_ik.L", "MCH-upper_arm_ik_target.L"]', 
ctrl_bones='["upper_arm_ik.L", "hand_ik.L", "upper_arm_ik_target.L"]', 
extra_ctrls='[""]', 
use_pole=True)


Glad I sorted it.
Still if someone from the Rigify team eventually spots this I'd like you to consider NOT changing function signatures without documenting and publishing your changes...