I decided I could wait to use the facilities until after I'd snapped a pic and moved the critter outside. I don't know what it is, and don't know how to begin to find out. It climbed onto my hand fairly willingly for a ride to the great outdoors--where it sat on the doormat until I came out again and moved it to the garden.
I have a feeling it might be some species of assassin bug--but that might be entirely wrong. I'll ask the folks at What's that bug?, if I can't find it on their site, and report.