fix(signal): send PresenceList directly to new client after ack

The broadcast alone wasn't reaching the first client because its
recv loop hadn't started yet when the second client registered.
Now the relay sends PresenceList directly to the new client (right
after RegisterPresenceAck) AND broadcasts to all others.

This guarantees every client gets the full user list:
- New client: via direct send (queued before recv loop starts)
- Existing clients: via broadcast

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-client/src/featherchat.rs

@@ -138,6 +138,7 @@ pub fn signal_to_call_type(signal: &SignalMessage) -> CallSignalType {
         | SignalMessage::UpgradeResponse { .. }
         | SignalMessage::UpgradeConfirm { .. }
         | SignalMessage::QualityCapability { .. } => CallSignalType::Offer, // quality negotiation
+        SignalMessage::PresenceList { .. } => CallSignalType::Offer, // lobby presence
         SignalMessage::QualityDirective { .. } => CallSignalType::Offer, // relay-initiated
     }
 }

crates/wzp-proto/src/lib.rs

@@ -27,7 +27,7 @@ pub use codec_id::{CodecId, QualityProfile};
 pub use error::*;
 pub use packet::{
     CallAcceptMode, HangupReason, MediaHeader, MediaPacket, MiniFrameContext, MiniHeader,
-    QualityReport, RoomParticipant, SignalMessage, TrunkEntry, TrunkFrame, FRAME_TYPE_FULL,
+    PresenceUser, QualityReport, RoomParticipant, SignalMessage, TrunkEntry, TrunkFrame, FRAME_TYPE_FULL,
     FRAME_TYPE_MINI,
 };
 pub use bandwidth::{BandwidthEstimator, CongestionState};

crates/wzp-proto/src/packet.rs

@@ -156,6 +156,14 @@ impl MediaHeader {
     }
 }
 
+/// A user visible in the signal presence list.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct PresenceUser {
+    pub fingerprint: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub alias: Option<String>,
+}
+
 /// Quality report appended to a media packet when Q flag is set (4 bytes).
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct QualityReport {
@@ -1020,6 +1028,16 @@ pub enum SignalMessage {
         reason: Option<String>,
     },
 
+    // ── Signal presence ───────────────────────────────────────────
+
+    /// Relay broadcasts the list of currently registered signal
+    /// users to all connected clients. Sent on every register/
+    /// deregister so clients can maintain a live lobby user list.
+    PresenceList {
+        /// List of online users. Each entry is { fingerprint, alias }.
+        users: Vec<PresenceUser>,
+    },
+
     // ── Quality upgrade negotiation (#28, #29) ──────────────────
 
     /// Peer proposes upgrading to a higher quality profile.

crates/wzp-relay/src/main.rs

@@ -1016,6 +1016,19 @@ async fn main() -> anyhow::Result<()> {
 
                 info!(%addr, fingerprint = %client_fp, alias = ?client_alias, "signal client registered");
 
+                // Send the full presence list directly to the new
+                // client (guaranteed delivery — their recv loop is
+                // about to start). Then broadcast to all OTHER
+                // clients so they learn about the new user.
+                {
+                    let hub = signal_hub.lock().await;
+                    let presence = hub.presence_list();
+                    // Direct send to new client (arrives right after ack)
+                    let _ = transport.send_signal(&presence).await;
+                    // Broadcast to everyone else
+                    hub.broadcast(&presence).await;
+                }
+
                 // Signal recv loop
                 loop {
                     match transport.recv_signal().await {
@@ -1560,6 +1573,9 @@ async fn main() -> anyhow::Result<()> {
                 {
                     let mut hub = signal_hub.lock().await;
                     hub.unregister(&client_fp);
+                    // Broadcast updated presence to remaining clients
+                    let presence_msg = hub.presence_list();
+                    hub.broadcast(&presence_msg).await;
                 }
                 {
                     let mut reg = presence.lock().await;

crates/wzp-relay/src/signal_hub.rs

@@ -86,6 +86,26 @@ impl SignalHub {
     pub fn alias(&self, fp: &str) -> Option<&str> {
         self.clients.get(fp).and_then(|c| c.alias.as_deref())
     }
+
+    /// Build a PresenceList message with all online users.
+    pub fn presence_list(&self) -> SignalMessage {
+        let users: Vec<wzp_proto::PresenceUser> = self
+            .clients
+            .values()
+            .map(|c| wzp_proto::PresenceUser {
+                fingerprint: c.fingerprint.clone(),
+                alias: c.alias.clone(),
+            })
+            .collect();
+        SignalMessage::PresenceList { users }
+    }
+
+    /// Broadcast a message to ALL connected signal clients.
+    pub async fn broadcast(&self, msg: &SignalMessage) {
+        for client in self.clients.values() {
+            let _ = client.transport.send_signal(msg).await;
+        }
+    }
 }
 
 #[cfg(test)]

desktop/src-tauri/src/lib.rs

@@ -1451,6 +1451,20 @@ fn do_register_signal(
                         });
                     }
                 }
+                Ok(Some(SignalMessage::PresenceList { users })) => {
+                    tracing::info!(count = users.len(), "signal: PresenceList received");
+                    // Emit to JS frontend for lobby user list
+                    let user_list: Vec<serde_json::Value> = users.iter().map(|u| {
+                        serde_json::json!({
+                            "fingerprint": u.fingerprint,
+                            "alias": u.alias,
+                        })
+                    }).collect();
+                    let _ = app_clone.emit("signal-event", serde_json::json!({
+                        "type": "presence_list",
+                        "users": user_list,
+                    }));
+                }
                 Ok(Some(SignalMessage::UpgradeProposal { call_id, proposal_id, proposed_profile, local_loss_pct, local_rtt_ms })) => {
                     tracing::info!(%call_id, %proposal_id, ?proposed_profile, "signal: UpgradeProposal from peer");
                     emit_call_debug(&app_clone, "recv:UpgradeProposal", serde_json::json!({