I am not sure what your old joke about the coin has to do with anything we are discussing.
If you deny that we live in a universe of “uniformity of causes in a closed system” which I take to mean an Objective reality then you have abandoned reason and there is no basis for us to continue discussion any further.
By analogy, one may set up an experiment in a chem lab, lock the door, and leave it to run overnight.
The results are assumed to be a fair test, that is, none of the grad students snuck into the lab overnight to retrieve their own glassware, and in doing so, turned off the electricity to your heater for half an hour.
Materialism assumes that there is not, never was, never can be, any external forces which cannot be controlled for (no supernatural).
How does one actually test that *rigorously* ? It is a philosophical assumption hiding behind the cloak of rationality: but it is not justified by the experimental results.
You are over-relying upon Occam's razor, which is useful for eliminating false positives, but isn't so hot at preventing false negatives.
Nice try, though.
Cheers!