Well, in case of a one shot, just make the box only for that row, but in a different colour, solved. If the user fails to set the sample as one-shot in the sample settings, but still uses it as one, then there is of course nothing you can do about it.
Oh wait, I totally forgot that one-shot mode has this bug: https://forum.renoise.com/t/new-note-columns-created-when-recording-one-shot-samples/41722. That makes things more tricky of course, as users use very long envelopes as a workaround for one-shot mode. And if this would be shown as very long notes in the pattern editor, it would again not reflect what is actually happening.