Okay, I diagnosed why nothing was moving: the power supply shipped in the kit was wired to the RAMPS terminal block with polarity reversed. Thankfully, the RAMPS seemed to handle that well — the power supply sunk its little heart into the RAMPS board, and its voltage dropped to half a volt, but the RAMPS didn’t let the smoke out. I swapped the polarity, and Houston: We. Have. Motion!
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