I find that my test audience expect the "grabbing an item and moving it" to work like a smartphone and so they try to pickup by holding the mouse button pressed and releasing by releasing the mouse button. Rather than explaining the issue of "click the mouse to pick up, click again to release", I'll instead try to conform the game to the audience.
This calls for AGS to recognize in repeatedly_execute that a mouse button is pressed. Sort of like a bastard between IsKeyPressed and on_mouse_click.
Is this possible?
Maybe mouse.IsButtonDown(e[...]) is what you are looking for?
That's the baby :-D