Nevermind. The answer is "EwmhBaseStruts", and the behavior I'm seeing is because I recently increased the size of all my buttons. So there was still a reserved area -- it just wasn't big enough.
BTW, I'm amused that I found the answer by asking ChatGPT: > I use fvwm as my window manager. How do I tell it that some areas > of the screen are off-limits for window placement? I use > "CleverPlacement". It gave a perfectly reasonable answer, and I knew right where to look. paul I wrote: > I feel like I used to know how to do this, or maybe I didn't, and it > worked properly in the past and I've changed something unknowingly. > > How do I tell CleverPlacement that some areas of the screen are off > limits? As things are, windows often end up on top of my FvwmButtons, > and my launcher buttons. > > (fvwm 2.6.8) > > paul > =---------------------- > paul fox, p...@foxharp.boston.ma.us (arlington, ma, where it's 43.0 degrees) > > =---------------------- paul fox, p...@foxharp.boston.ma.us (arlington, ma, where it's 43.4 degrees)