Security hardening: log redaction + 5 trust-boundary fixes (S10, T1/T2/T5/T6/T7)

Codex (gpt-5.5) implementer branch, senior-reviewed.

- S10 (High): redact capabilities/chat from logs; create log 0600 + chmod
  existing; rotate at 5 MiB. New short_id/short_bytes_hex/redact_for_log seams.
- T1 (P2): friends-ALPN authorizes (handler(from)) before reading any peer
  bytes; unauthorized conns closed pre-read (DoS relief).
- T2 (P2): per-(author,kind) replay gate on state-changing gossip (Announce/
  Leave) only; Chat bypasses it, preserving the S2 no-monotonic-ts decision.
- T5 (P2): cap inbound Opus datagrams at 4 + MAX_OPUS_PAYLOAD (4000).
- T6 (P2): bind friend-Pong room ticket host to the authenticated responder
  (interpret_pong/probe now thread the remote id) — blocks Join-button
  redirect/phishing. Non-regressive given the W7 P3 restamp design.
- T7 (P3): sanitize_ticket caps/validates PeerState.sharing at gossip ingest
  so invalid offers never render a Watch button.

302 lib tests pass (was 291), clippy --all-targets clean, release builds.
Tests-green only; DoS relief + 2-machine replay/redirect behavior want a
field test. W7 P7 (n0 DNS privacy) reviewed read-only — findings to triage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/presence.rs

@@ -110,26 +110,32 @@ pub enum FriendPresence {
     InRoom { name: String, ticket: String },
 }
 
-/// Interpret a peer's reply defensively. Only a `Pong` is a reply (a `Ping` is
-/// not, so it yields `None`). When the peer reports a room, we **sanitize the
-/// peer-supplied name** and **only surface it as joinable if the ticket actually
-/// parses** as a [`crate::network::PeerSpeakTicket`] — a garbage or hostile
-/// ticket downgrades the friend to plain `Online` rather than offering a dead /
-/// dangerous Join button. (We still never auto-join; the user clicks.)
-pub fn interpret_pong(msg: &ControlMsg) -> Option<FriendPresence> {
+/// Interpret a peer's reply defensively. `from` must be the connection's
+/// authenticated remote id, not any value carried in the payload. Only a `Pong`
+/// is a reply (a `Ping` is not, so it yields `None`). When the peer reports a
+/// room, we **sanitize the peer-supplied name** and **only surface it as joinable
+/// if the ticket actually parses** as a [`crate::network::PeerSpeakTicket`] and
+/// points back at the replying friend. A garbage/redirect ticket downgrades the
+/// friend to plain `Online` rather than offering a dead or attacker-controlled
+/// Join button. (We still never auto-join; the user clicks.)
+pub fn interpret_pong(msg: &ControlMsg, from: EndpointId) -> Option<FriendPresence> {
     match msg {
         ControlMsg::Ping => None,
         ControlMsg::Pong { room: None } => Some(FriendPresence::Online),
         ControlMsg::Pong { room: Some(r) } => {
-            if r.ticket.parse::<crate::network::PeerSpeakTicket>().is_ok() {
-                Some(FriendPresence::InRoom {
-                    name: crate::sanitize::sanitize_name(&r.name),
-                    ticket: r.ticket.clone(),
-                })
-            } else {
+            let Ok(ticket) = r.ticket.parse::<crate::network::PeerSpeakTicket>() else {
                 // Online, but the advertised room is unusable — don't offer Join.
-                Some(FriendPresence::Online)
+                return Some(FriendPresence::Online);
+            };
+            if ticket.host_addr.id != from {
+                // Online, but the advertised room redirects away from the friend
+                // who authenticated this Pong — don't offer a phishing Join.
+                return Some(FriendPresence::Online);
             }
+            Some(FriendPresence::InRoom {
+                name: crate::sanitize::sanitize_name(&r.name),
+                ticket: r.ticket.clone(),
+            })
         }
     }
 }
@@ -206,21 +212,22 @@ mod tests {
 
     #[test]
     fn interpret_ping_is_not_a_reply() {
-        assert_eq!(interpret_pong(&ControlMsg::Ping), None);
+        assert_eq!(interpret_pong(&ControlMsg::Ping, id()), None);
     }
 
     #[test]
     fn interpret_pong_online_and_inroom() {
+        let friend = id();
         // No room -> Online.
         assert_eq!(
-            interpret_pong(&ControlMsg::Pong { room: None }),
+            interpret_pong(&ControlMsg::Pong { room: None }, friend),
             Some(FriendPresence::Online)
         );
         // Valid ticket -> InRoom with a sanitized name.
-        let t = valid_ticket(id());
+        let t = valid_ticket(friend);
         let got = interpret_pong(&ControlMsg::Pong {
             room: Some(RoomPresence { name: "HangOut".into(), ticket: t.clone() }),
-        });
+        }, friend);
         assert_eq!(got, Some(FriendPresence::InRoom { name: "HangOut".into(), ticket: t }));
     }
 
@@ -230,17 +237,29 @@ mod tests {
         // Online — no dead/hostile Join button is surfaced.
         let got = interpret_pong(&ControlMsg::Pong {
             room: Some(RoomPresence { name: "Trap".into(), ticket: "not-a-ticket".into() }),
-        });
+        }, id());
+        assert_eq!(got, Some(FriendPresence::Online));
+    }
+
+    #[test]
+    fn interpret_pong_rejects_ticket_for_a_different_host() {
+        let friend = id();
+        let attacker = id();
+        let t = valid_ticket(attacker);
+        let got = interpret_pong(&ControlMsg::Pong {
+            room: Some(RoomPresence { name: "Redirect".into(), ticket: t }),
+        }, friend);
         assert_eq!(got, Some(FriendPresence::Online));
     }
 
     #[test]
     fn interpret_pong_sanitizes_a_hostile_room_name() {
         // Control/bidi characters in a peer-supplied name are stripped.
-        let t = valid_ticket(id());
+        let friend = id();
+        let t = valid_ticket(friend);
         let got = interpret_pong(&ControlMsg::Pong {
             room: Some(RoomPresence { name: "Hang\u{202e}Out\u{0007}".into(), ticket: t.clone() }),
-        });
+        }, friend);
         match got {
             Some(FriendPresence::InRoom { name, .. }) => {
                 assert!(!name.contains('\u{202e}'), "bidi override must be stripped");