@ckeen whenever some parts of the layout change, the respective changer ought to send #layoutChanged. This is not done in every case, but most relevant. I'm not sure it is done for plain morphs, tho, maybe only for tools. #changed and #changed: are sent more often…

Look at the 'layout' category, there's a lot of stuff happening.

But look at #extent:of Morph. While not always when the layout changes, the size of a morph changes, everytime the size changes, also the layout change is issued.

@ckeen Ah. BTW: have you tried overriding #layoutChanged ?