feat: Tauri desktop GUI app with call engine

- New desktop/ directory with Tauri v2 + Vite + TypeScript
- Rust backend: CallEngine wrapping wzp-client audio + transport
- Web frontend: connect screen, in-call screen with participants,
  mic/speaker mute, keyboard shortcuts (m/s/q)
- Dark theme UI, settings persistence via localStorage
- Platform-aware --os-aec: warns on Windows/Linux (not yet implemented)
- Workspace updated to include desktop/src-tauri

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

desktop/src-tauri/src/engine.rs

@@ -0,0 +1,288 @@
+//! Call engine for the desktop app — wraps wzp-client audio + transport
+//! into a clean async interface for Tauri commands.
+
+use std::net::SocketAddr;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+
+use tokio::sync::Mutex;
+use tracing::{error, info};
+
+use wzp_client::audio_io::{AudioCapture, AudioPlayback};
+use wzp_client::call::{CallConfig, CallEncoder};
+use wzp_proto::MediaTransport;
+
+const FRAME_SAMPLES: usize = 960;
+
+pub struct ParticipantInfo {
+    pub fingerprint: String,
+    pub alias: Option<String>,
+}
+
+pub struct EngineStatus {
+    pub mic_muted: bool,
+    pub spk_muted: bool,
+    pub participants: Vec<ParticipantInfo>,
+    pub frames_sent: u64,
+    pub frames_received: u64,
+}
+
+pub struct CallEngine {
+    running: Arc<AtomicBool>,
+    mic_muted: Arc<AtomicBool>,
+    spk_muted: Arc<AtomicBool>,
+    participants: Arc<Mutex<Vec<ParticipantInfo>>>,
+    frames_sent: Arc<std::sync::atomic::AtomicU64>,
+    frames_received: Arc<std::sync::atomic::AtomicU64>,
+    transport: Arc<wzp_transport::QuinnTransport>,
+}
+
+impl CallEngine {
+    pub async fn start<F>(
+        relay: String,
+        room: String,
+        alias: String,
+        _os_aec: bool,
+        event_cb: F,
+    ) -> Result<Self, anyhow::Error>
+    where
+        F: Fn(&str, &str) + Send + Sync + 'static,
+    {
+        let _ = rustls::crypto::ring::default_provider().install_default();
+
+        let relay_addr: SocketAddr = relay.parse()?;
+
+        // Load or generate identity
+        let seed = {
+            let path = {
+                let home = std::env::var("HOME").unwrap_or_else(|_| ".".into());
+                std::path::PathBuf::from(home).join(".wzp").join("identity")
+            };
+            if path.exists() {
+                if let Ok(hex) = std::fs::read_to_string(&path) {
+                    if let Ok(s) = wzp_crypto::Seed::from_hex(hex.trim()) {
+                        s
+                    } else {
+                        wzp_crypto::Seed::generate()
+                    }
+                } else {
+                    wzp_crypto::Seed::generate()
+                }
+            } else {
+                let s = wzp_crypto::Seed::generate();
+                if let Some(p) = path.parent() {
+                    std::fs::create_dir_all(p).ok();
+                }
+                let hex: String = s.0.iter().map(|b| format!("{b:02x}")).collect();
+                std::fs::write(&path, hex).ok();
+                s
+            }
+        };
+
+        let fp = seed.derive_identity().public_identity().fingerprint;
+        info!(%fp, "identity loaded");
+
+        // Connect
+        let bind_addr: SocketAddr = "0.0.0.0:0".parse().unwrap();
+        let endpoint = wzp_transport::create_endpoint(bind_addr, None)?;
+        let client_config = wzp_transport::client_config();
+        let conn = wzp_transport::connect(&endpoint, relay_addr, &room, client_config).await?;
+        let transport = Arc::new(wzp_transport::QuinnTransport::new(conn));
+
+        // Handshake
+        let _session = wzp_client::handshake::perform_handshake(
+            &*transport,
+            &seed.0,
+            Some(&alias),
+        )
+        .await?;
+
+        info!("connected to relay, handshake complete");
+        event_cb("connected", &format!("joined room {room}"));
+
+        // Audio I/O
+        // TODO: support VPIO on macOS when os_aec is true
+        let capture = AudioCapture::start()?;
+        let playback = AudioPlayback::start()?;
+        let capture_ring = capture.ring().clone();
+        let playout_ring = playback.ring().clone();
+        std::mem::forget(capture);
+        std::mem::forget(playback);
+
+        let running = Arc::new(AtomicBool::new(true));
+        let mic_muted = Arc::new(AtomicBool::new(false));
+        let spk_muted = Arc::new(AtomicBool::new(false));
+        let participants: Arc<Mutex<Vec<ParticipantInfo>>> = Arc::new(Mutex::new(vec![]));
+        let frames_sent = Arc::new(std::sync::atomic::AtomicU64::new(0));
+        let frames_received = Arc::new(std::sync::atomic::AtomicU64::new(0));
+
+        // Send task
+        let send_t = transport.clone();
+        let send_r = running.clone();
+        let send_mic = mic_muted.clone();
+        let send_fs = frames_sent.clone();
+        tokio::spawn(async move {
+            let config = CallConfig {
+                noise_suppression: false,
+                suppression_enabled: false,
+                ..CallConfig::default()
+            };
+            let mut encoder = CallEncoder::new(&config);
+            encoder.set_aec_enabled(false); // OS AEC or none
+            let mut buf = vec![0i16; FRAME_SAMPLES];
+
+            loop {
+                if !send_r.load(Ordering::Relaxed) {
+                    break;
+                }
+                if capture_ring.available() < FRAME_SAMPLES {
+                    tokio::time::sleep(std::time::Duration::from_millis(5)).await;
+                    continue;
+                }
+                capture_ring.read(&mut buf);
+                if send_mic.load(Ordering::Relaxed) {
+                    buf.fill(0);
+                }
+                match encoder.encode_frame(&buf) {
+                    Ok(pkts) => {
+                        for pkt in &pkts {
+                            if let Err(e) = send_t.send_media(pkt).await {
+                                error!("send: {e}");
+                                return;
+                            }
+                        }
+                        send_fs.fetch_add(1, Ordering::Relaxed);
+                    }
+                    Err(e) => error!("encode: {e}"),
+                }
+            }
+        });
+
+        // Recv task (direct playout)
+        let recv_t = transport.clone();
+        let recv_r = running.clone();
+        let recv_spk = spk_muted.clone();
+        let recv_fr = frames_received.clone();
+        tokio::spawn(async move {
+            let mut opus_dec = wzp_codec::create_decoder(wzp_proto::QualityProfile::GOOD);
+            let mut agc = wzp_codec::AutoGainControl::new();
+            let mut pcm = vec![0i16; FRAME_SAMPLES];
+
+            loop {
+                if !recv_r.load(Ordering::Relaxed) {
+                    break;
+                }
+                match tokio::time::timeout(
+                    std::time::Duration::from_millis(100),
+                    recv_t.recv_media(),
+                )
+                .await
+                {
+                    Ok(Ok(Some(pkt))) => {
+                        if !pkt.header.is_repair {
+                            if let Ok(n) = opus_dec.decode(&pkt.payload, &mut pcm) {
+                                agc.process_frame(&mut pcm[..n]);
+                                if !recv_spk.load(Ordering::Relaxed) {
+                                    playout_ring.write(&pcm[..n]);
+                                }
+                            }
+                        }
+                        recv_fr.fetch_add(1, Ordering::Relaxed);
+                    }
+                    Ok(Ok(None)) => break,
+                    Ok(Err(e)) => {
+                        error!("recv: {e}");
+                        break;
+                    }
+                    Err(_) => {}
+                }
+            }
+        });
+
+        // Signal task (presence)
+        let sig_t = transport.clone();
+        let sig_r = running.clone();
+        let sig_p = participants.clone();
+        let event_cb = Arc::new(event_cb);
+        let sig_cb = event_cb.clone();
+        tokio::spawn(async move {
+            loop {
+                if !sig_r.load(Ordering::Relaxed) {
+                    break;
+                }
+                match tokio::time::timeout(
+                    std::time::Duration::from_millis(200),
+                    sig_t.recv_signal(),
+                )
+                .await
+                {
+                    Ok(Ok(Some(wzp_proto::SignalMessage::RoomUpdate {
+                        participants: parts,
+                        ..
+                    }))) => {
+                        let mut seen = std::collections::HashSet::new();
+                        let unique: Vec<ParticipantInfo> = parts
+                            .into_iter()
+                            .filter(|p| seen.insert((p.fingerprint.clone(), p.alias.clone())))
+                            .map(|p| ParticipantInfo {
+                                fingerprint: p.fingerprint,
+                                alias: p.alias,
+                            })
+                            .collect();
+                        let count = unique.len();
+                        *sig_p.lock().await = unique;
+                        sig_cb("room-update", &format!("{count} participants"));
+                    }
+                    Ok(Ok(Some(_))) => {}
+                    Ok(Ok(None)) => break,
+                    Ok(Err(_)) => break,
+                    Err(_) => {}
+                }
+            }
+        });
+
+        Ok(Self {
+            running,
+            mic_muted,
+            spk_muted,
+            participants,
+            frames_sent,
+            frames_received,
+            transport,
+        })
+    }
+
+    pub fn toggle_mic(&self) -> bool {
+        let was = self.mic_muted.load(Ordering::Relaxed);
+        self.mic_muted.store(!was, Ordering::Relaxed);
+        !was
+    }
+
+    pub fn toggle_speaker(&self) -> bool {
+        let was = self.spk_muted.load(Ordering::Relaxed);
+        self.spk_muted.store(!was, Ordering::Relaxed);
+        !was
+    }
+
+    pub fn status(&self) -> EngineStatus {
+        let parts = self.participants.blocking_lock();
+        EngineStatus {
+            mic_muted: self.mic_muted.load(Ordering::Relaxed),
+            spk_muted: self.spk_muted.load(Ordering::Relaxed),
+            participants: parts
+                .iter()
+                .map(|p| ParticipantInfo {
+                    fingerprint: p.fingerprint.clone(),
+                    alias: p.alias.clone(),
+                })
+                .collect(),
+            frames_sent: self.frames_sent.load(Ordering::Relaxed),
+            frames_received: self.frames_received.load(Ordering::Relaxed),
+        }
+    }
+
+    pub async fn stop(self) {
+        self.running.store(false, Ordering::SeqCst);
+        self.transport.close().await.ok();
+    }
+}