I noticed when I put them to bed yesterday that they'd eaten all of their food, which is very unusual. Generally I just need to top it up every other day or so. This morning, someone had clearly been fussing around in the nest box, but the egg itself was over on the other side of the coop. Probably they need a few rounds to figure out what the physical sensations mean and how the timing works.
The egg is small but nicely formed. I will update with a picture when I get back home.
I expect it's Teckla's, since she looks more mature, but these breeds have fairly similar-looking eggs so it will be hard to tell who's done what unless I catch them in the act.
(Next to a store-bought egg, for scale.)