Well, maybe the answer is that "pressing any button will cease the dim-down", nothing more. (that way you don't care if you got the WRONG keypress, just so long as you "got one"..if there is enough lead-time involved (a couple seconds), then if it MISSES a keypress, the user can always press again and still have time to deal with it.

Alternatively, it could a "hold-on-poweron" (e.g., hold the left button down at ignition to reset both dimmer settings to 100%)

Thinking out loud...

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