When the user leaves the 'label format' blank, and pops out or closes the embedded app, the plugin becomes 'transparent' on the panel. Essentially invisible. In such cases it would help if it had a handle, in the style of Windows Buttons. This could also be provided as an option in the Display section of the Embed Properties.
How about setting the label format to a single space, or to "..."?
I did try putting a space, but the plugin stays as invisible as ever: You really have to look hard to find where it is supposed to be when no app is embedded. Putting a ... or what else feels hacky. I think a handle would be a useful addition.
I'll look into adding it at some point, but in the meantime, try unicode: ▫ (character 0x25AB).
Added to master. Try it out.
Looks excellent. Thanks.