docs: mark W7 P4 pure core done (presence protocol + auth gate)

docs/contacts-plan.md

@@ -115,16 +115,20 @@ address book), though a lightweight mutual-add is optional polish.
   needs a ticket struct change) and tighter ticket encoding (drop JSON/base64 fat,
   index the relay URL; lossless ~halving).
 
-### P4 — Friends-only idle listener + presence — Medium (the new primitive)
-A long-lived endpoint while the app is open (own ALPN, e.g. `peerspeak/friends/0`),
-**outside** the room-session lifecycle, that:
-- answers a ping only if `remote_id()` ∈ friends list;
-- replies with online + (if in a gathering) a fresh member-issued ticket + the
-  cosmetic room name;
-- is governed by the invisible/normal/discoverable state.
-On app open (and a slow rate-limited refresh), ping each friend; render their
-status in the friends list. If a friend reports a gathering, show a small
-**room-name tag + Join** entry; clicking bootstraps off their ticket.
+### P4 — Friends-only idle listener + presence — pure core DONE 2026-06-15 (`a897f5c`)
+- **Pure protocol + policy DONE** (`src/presence.rs`, +8 tests): `ControlMsg`
+  {Ping, Pong{room: Option<RoomPresence>}} (tagged JSON, unknown tags rejected);
+  `should_answer(from, friends, mode)` — the friends-only + not-invisible auth gate
+  (the anti-stranger-surface whitelist; `from` = authenticated `remote_id`);
+  `PresenceMode` {Invisible, Normal(default), Discoverable} persisted in
+  `AppConfig`; `interpret_pong` — defensive (sanitizes peer room name, only
+  surfaces a joinable room if the ticket parses, never auto-joins).
+- **Deferred to a 2-machine session (the I/O edges):** bind the live control
+  endpoint on its own ALPN (e.g. `peerspeak/friends/0`) **outside** the room
+  session lifecycle; its accept loop (gated by `should_answer`); the rate-limited
+  outbound ping scheduler (on app open + slow refresh); reporting our current
+  gathering as a member-issued ticket (reuse `restamp`); rendering friend status +
+  a **room-name tag + Join** entry in the friends list (overlaps P5).
 
 ### P5 — Recents + UI — Medium
 Local recents list (cosmetic room tags). Friends-list UI with status dots