Thanks for replying. I was able to find a workaround.
On my Mini, the machine believes the gap between its upper Z limit switch and the top part of the wiping pad is less than it truly is. At the very top of the Z axis travel, issuing the M114 command shows a Z coordinate of 158.00. At the top of the wiper pad, the coordinate is -.90. The nominal value at the top of the wiper pad should be 1.8 - so there is a nearly 3mm error.
In this thread from 2018, user ScottW proposes a quick fix: modify Cura’s gcode preamble to add a new offset. Reproducing it here:
G28 ; home all axes
G92 Z161 ; manually set Z position to 161
G0 X0 Y187 Z156 F200 ; move away from endstops
Now my printer homes correctly. What a relief! Of course, this does not actually identify or resolve the root cause of the problem. My total time with this printer is 3 days, so I welcome any suggestions for a better fix.