Cool, that was quick! Btw I wasn't the first to use a JSFX to get MIDI, that was eugen2777 with his Retrospective Record script. It's not the same JSFX, but the same kind of thing.
(oh, from the comment in GitHub, the reason for the OR, idx|0x1000000 is that this is the flag set to tell Reaper the idx is an Input Effect)
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