Row 50 asks which WRAM reading tells a battle menu that is accepting input
from one that is only drawn, and the honest way to answer it is to press.
FLY_PROBE_CATCH=accept drives real battles, and on every battle frame it
exports the emulator state, issues one directional pulse, reads
wCurrentMenuItem and puts the state straight back -- so the run is not
perturbed by the measurement and every frame gets a ground truth.
Beside that it asks every byte of WRAM and HRAM whether its values on
accepting frames are disjoint from its values on refusing ones, so a
reading is found rather than nominated.
The pulse releases the buttons before it presses: JoypadLowSensitivity acts
on a key's edge, so a direction the fly is already holding reads as refused
for the measurement's reason and not the cartridge's.
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