So Windlanes are magical thread-like things that go in and out of words and connect other words together.
The Shadow-Web is basically the Spiral but in the shape of a spider web.
Morganthe wanted to completely destroy the Spiral and create the Shadow-Web, but is the Shadow-Web already here? In the Khrysalis history quest Old Cob says "The Shadow-Web hums and stretches beyond the starts, touching all the Spiral, with Spider's welcoming arms." This kind of sounds like the Shadow-Web is already in the Spiral. If you look at the picture in that quest, it shows the Shadow-Web AND the Spiral, not just one. This makes me think that Windlanes are the Shadow-Web. Just a thought.