🚀 go-pugleaf

    I got it to grow from about 720 to 888 (with a max of 1016) simply
    by moving already existing windows around.

That by itself is not an indication of a memory leak.  Moving windows around,
most particularly when nonrectangular windows are on the screen, is not a free
operation, the server is maintaining various kinds of region descriptions, and
as you move windows those regions can get more complicated.  You also generate
exposure events, which can potentially cause more output buffers to be
allocated (depends on previous history).  If you have backing-store enable
anywhere, that can also cause memory allocation.  I don't see anything
particularly alarming in those numbers, per se.