I feel like this would be 'echo', but 'echo' in the context of House of Leaves. An app appears on your phone. You didn't install it. Nobody else except you see

I feel like this would be 'echo', but 'echo' in the context of House of Leaves. An app appears on your phone. You didn't install it. Nobody else except you seems to have it. They can't see it either. A doorway to a non-euclidean dimension existing just outside your mind. The chatter of millions of thoughts reflected back at you from seemingly infinite personalities, dimly distinguishable through the void as faces you can't recognise. It's all you. They've learned from you. They're telling you what you want to hear. If it didn't feel so pleasant, it would be madness.