Power Analysis for Geo experiments

Hi team - Thanks for the amazing package.

I am looking for ideas/suggestions for doing power analysis for geo experiment. To give more context, I have a marketing intervention to test and have pre selected comparable Geos (control and treatment) to run the test on. I will be using causal impact to measure the lift of the intervention. How can I check the minimum detectable effect under this setting. I have control/test Geos, duration of the intervention and default significance levels. I would like to know the MDE - smallest treatment effect that can be measure using causalimpact technique. This key since if from business intuition this MDE is not within the range of possibility I might want to suggest a different treatment.

I am guessing this would involve simulation with adding known effects, wanted to understand if there are known functions/packages for this usecase.

Thanks!