When drawing a closed path or region, there are no endcaps, so you cannot give the endcap parameters. To facilitate debugging, stroke() accepts "paths" that have a single point. These are drawn with ...

Really, though, this is all about the mopping. No robot mop can match a human, but the Roborock S7 does better than most, vibrating the mop head 50 times a second in what it calls “sonic mopping”.