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Hello Jason,
I know you are busy 'waging battles on all fronts' so just to clarify: Inertial mass and gravitational mass must be identical to satisfy the Equivalence Principle, and so they are ASSUMED to be identical in General Relativity.
Before I continue, I should perhaps mention that where SR and GR have been compared and empirically tested, GR has always shown to be correct. The big question in GR with respect to 'foundations' is described below.
The Equivalence Principle basically asserts that small, freely falling frames in the presence of gravity are equivalent to inertial frames in the absence of gravity. So as you fall freely, towards say a black hole, you are weightless, and it seems as if there is no gravity in your vicinity. But the Equivalence Principle ignores tidal gravity, which also stretches you from head to foot and squeezes you from the sides (spaghetification). However, if you were the size of an ant you would experience less tidal gravity, than if you were the size of a whale. The question is, then, just how small must a freely falling frame of reference have to be, to justify ignoring tidal gravity completely? Or is the existence of inertial (gravity-free) frames never justified?
I hope that answers your question.
Robert