@whale-av Yeah, I was afraid of that.
Thanks for the link. It's basically the same use case. LFOs are relatively straightforward because you expect them to be changing continuously. Envelopes are not so straightforward, because they might fall to a zero level and stay there for some time until triggered again. As you suggested, you could fall to "almost 0" but it still seems an awkward workaround (especially for students who are having trouble remembering the medium-sized print without facing fine print like this).
Brainstorm: What if, in a future version of Pd, [inlet~] had a right outlet that would output a control message 0 for unconnected and 1 for connected? Control message because it would be wasteful to run a signal for that -- although then, I suppose you would need a "bang" inlet to poll the connection state.