feat(appd): add WebSocket UI endpoint for Servo shell integration

Implements the weft-appd WebSocket server that allows the system-ui.html
page running inside Servo to send requests and receive push notifications
without requiring custom SpiderMonkey bindings.

ws.rs — WebSocket connection handler:
- Accepts a tokio TcpStream, performs WebSocket handshake via
  tokio-tungstenite accept_async.
- Reads JSON Text frames, deserializes as Request (serde_json), calls
  dispatch(), sends Response as JSON Text.
- Subscribes to a broadcast::Receiver<Response> for server-push
  notifications (APP_READY, etc.); forwards to client via select!.
- Handles close frames, partial errors, and lagged broadcast gracefully.

main.rs — server changes:
- broadcast::channel(16) created at startup; WebSocket handlers
  subscribe for push delivery.
- TcpListener bound on 127.0.0.1:7410 (default) or WEFT_APPD_WS_PORT.
- ws_port() / write_ws_port(): port written to
  XDG_RUNTIME_DIR/weft/appd.wsport for runtime discovery.
- WS accept branch added to the main select! loop alongside Unix socket.

ipc.rs — Response and AppStateKind now derive Clone (required by
broadcast::Sender<Response>).

system-ui.html — appd WebSocket client:
- appdConnect(): opens ws://127.0.0.1:<port>/appd with exponential
  backoff reconnect (1s → 16s max).
- On open: sends QUERY_RUNNING to populate taskbar with live sessions.
- handleAppdMessage(): maps LAUNCH_ACK and RUNNING_APPS to taskbar
  entries; APP_READY shows a timed notification; APP_STATE::stopped
  removes the taskbar entry.
- WEFT_APPD_WS_PORT window global overrides the default port.

New deps: tokio-tungstenite 0.24, futures-util 0.3 (sink+std),
serde_json 1.

Cargo.lock

@@ -158,6 +158,12 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "byteorder"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fd0f2584146f6f2ef48085050886acf353beff7305ebd1ae69500e27c67f64b"
+
 [[package]]
 name = "bytes"
 version = "1.11.1"
@@ -343,6 +349,12 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f27ae1dd37df86211c42e150270f82743308803d90a6f6e6651cd730d5e1732f"
 
+[[package]]
+name = "data-encoding"
+version = "2.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7a1e2f27636f116493b8b860f5546edb47c8d8f8ea73e1d2a20be88e28d1fea"
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -488,6 +500,12 @@ version = "0.3.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7e3450815272ef58cec6d564423f6e755e25379b217b0bc688e295ba24df6b1d"
 
+[[package]]
+name = "futures-sink"
+version = "0.3.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c39754e157331b013978ec91992bde1ac089843443c49cbc7f46150b0fad0893"
+
 [[package]]
 name = "futures-task"
 version = "0.3.32"
@@ -501,6 +519,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "389ca41296e6190b48053de0321d02a77f32f8a5d2461dd38762c0593805c6d6"
 dependencies = [
  "futures-core",
+ "futures-sink",
  "futures-task",
  "pin-project-lite",
  "slab",
@@ -550,6 +569,17 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff2abc00be7fca6ebc474524697ae276ad847ad0a6b3faa4bcb027e9a4614ad0"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.3.4"
@@ -619,6 +649,22 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc0fef456e4baa96da950455cd02c081ca953b141298e41db3fc7e36b1da849c"
 
+[[package]]
+name = "http"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3ba2a386d7f85a81f119ad7498ebe444d2e22c2af0b86b069416ace48b3311a"
+dependencies = [
+ "bytes",
+ "itoa",
+]
+
+[[package]]
+name = "httparse"
+version = "1.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6dbf3de79e51f3d586ab4cb9d5c3e2c14aa28ed23d180cf89b4df0454a69cc87"
+
 [[package]]
 name = "id-arena"
 version = "2.3.0"
@@ -1325,14 +1371,35 @@ version = "6.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
 
+[[package]]
+name = "rand"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+dependencies = [
+ "libc",
+ "rand_chacha 0.3.1",
+ "rand_core 0.6.4",
+]
+
 [[package]]
 name = "rand"
 version = "0.9.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6db2770f06117d490610c7488547d543617b21bfa07796d7a12f6f1bd53850d1"
 dependencies = [
- "rand_chacha",
+ "rand_chacha 0.9.0",
- "rand_core",
+ "rand_core 0.9.5",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
+ "rand_core 0.6.4",
 ]
 
 [[package]]
@@ -1342,7 +1409,16 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d3022b5f1df60f26e1ffddd6c66e8aa15de382ae63b3a0c1bfc0e4d3e3f325cb"
 dependencies = [
  "ppv-lite86",
- "rand_core",
+ "rand_core 0.9.5",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+dependencies = [
+ "getrandom 0.2.17",
 ]
 
 [[package]]
@@ -1528,6 +1604,17 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "sha1"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3bf829a2d51ab4a5ddf1352d8470c140cadc8301b2ae1789db023f01cedd6ba"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "digest",
+]
+
 [[package]]
 name = "sha2"
 version = "0.10.9"
@@ -1604,7 +1691,7 @@ dependencies = [
  "libseat",
  "pkg-config",
  "profiling",
- "rand",
+ "rand 0.9.2",
  "rustix 1.1.4",
  "sha2",
  "smallvec",
@@ -1798,6 +1885,18 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "tokio-tungstenite"
+version = "0.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "edc5f74e248dc973e0dbb7b74c7e0d6fcc301c694ff50049504004ef4d0cdcd9"
+dependencies = [
+ "futures-util",
+ "log",
+ "tokio",
+ "tungstenite",
+]
+
 [[package]]
 name = "toml"
 version = "0.9.12+spec-1.1.0"
@@ -1920,6 +2019,24 @@ dependencies = [
  "tracing-log",
 ]
 
+[[package]]
+name = "tungstenite"
+version = "0.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "18e5b8366ee7a95b16d32197d0b2604b43a0be89dc5fac9f8e96ccafbaedda8a"
+dependencies = [
+ "byteorder",
+ "bytes",
+ "data-encoding",
+ "http",
+ "httparse",
+ "log",
+ "rand 0.8.5",
+ "sha1",
+ "thiserror 1.0.69",
+ "utf-8",
+]
+
 [[package]]
 name = "typenum"
 version = "1.19.0"
@@ -1956,6 +2073,12 @@ version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
 
+[[package]]
+name = "utf-8"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09cc8ee72d2a9becf2f2febe0205bbed8fc6615b7cb429ad062dc7b7ddd036a9"
+
 [[package]]
 name = "valuable"
 version = "0.1.1"
@@ -2275,10 +2398,13 @@ name = "weft-appd"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "futures-util",
  "rmp-serde",
  "sd-notify",
  "serde",
+ "serde_json",
  "tokio",
+ "tokio-tungstenite",
  "tracing",
  "tracing-subscriber",
 ]

crates/weft-appd/Cargo.toml

@@ -14,5 +14,8 @@ sd-notify = "0.4"
 tokio = { version = "1", features = ["rt-multi-thread", "macros", "net", "io-util", "signal", "sync"] }
 serde = { version = "1", features = ["derive"] }
 rmp-serde = "1"
+serde_json = "1"
+tokio-tungstenite = "0.24"
+futures-util = { version = "0.3", default-features = false, features = ["sink", "std"] }
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }

crates/weft-appd/src/ipc.rs

@@ -10,7 +10,7 @@ pub enum Request {
     QueryAppState { session_id: u64 },
 }
 
-#[derive(Debug, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(tag = "type", rename_all = "SCREAMING_SNAKE_CASE")]
 pub enum Response {
     LaunchAck {

crates/weft-appd/src/main.rs

@@ -6,10 +6,11 @@ use tokio::io::AsyncWriteExt;
 use tokio::sync::Mutex;
 
 mod ipc;
+mod ws;
 
 use ipc::{AppStateKind, Request, Response};
 
-type Registry = Arc<Mutex<SessionRegistry>>;
+pub(crate) type Registry = Arc<Mutex<SessionRegistry>>;
 
 #[derive(Default)]
 struct SessionRegistry {
@@ -65,9 +66,18 @@ async fn run() -> anyhow::Result<()> {
         .with_context(|| format!("bind {}", socket_path.display()))?;
     tracing::info!(path = %socket_path.display(), "IPC socket listening");
 
-    let _ = sd_notify::notify(false, &[sd_notify::NotifyState::Ready]);
-
     let registry: Registry = Arc::new(Mutex::new(SessionRegistry::default()));
+    let (broadcast_tx, _) = tokio::sync::broadcast::channel::<Response>(16);
+
+    let ws_port = ws_port();
+    let ws_addr: std::net::SocketAddr = format!("127.0.0.1:{ws_port}").parse()?;
+    let ws_listener = tokio::net::TcpListener::bind(ws_addr)
+        .await
+        .with_context(|| format!("bind WebSocket {ws_addr}"))?;
+    tracing::info!(addr = %ws_addr, "WebSocket listener ready");
+    write_ws_port(ws_port)?;
+
+    let _ = sd_notify::notify(false, &[sd_notify::NotifyState::Ready]);
 
     let mut shutdown = std::pin::pin!(tokio::signal::ctrl_c());
 
@@ -78,7 +88,17 @@ async fn run() -> anyhow::Result<()> {
                 let reg = Arc::clone(&registry);
                 tokio::spawn(async move {
                     if let Err(e) = handle_connection(stream, reg).await {
-                        tracing::warn!(error = %e, "connection error");
+                        tracing::warn!(error = %e, "unix connection error");
+                    }
+                });
+            }
+            result = ws_listener.accept() => {
+                let (stream, _) = result.context("ws accept")?;
+                let reg = Arc::clone(&registry);
+                let rx = broadcast_tx.subscribe();
+                tokio::spawn(async move {
+                    if let Err(e) = ws::handle_ws_connection(stream, reg, rx).await {
+                        tracing::warn!(error = %e, "ws connection error");
                     }
                 });
             }
@@ -93,6 +113,23 @@ async fn run() -> anyhow::Result<()> {
     Ok(())
 }
 
+fn ws_port() -> u16 {
+    std::env::var("WEFT_APPD_WS_PORT")
+        .ok()
+        .and_then(|s| s.parse().ok())
+        .unwrap_or(7410)
+}
+
+fn write_ws_port(port: u16) -> anyhow::Result<()> {
+    let runtime_dir = std::env::var("XDG_RUNTIME_DIR").context("XDG_RUNTIME_DIR not set")?;
+    let path = PathBuf::from(runtime_dir).join("weft/appd.wsport");
+    if let Some(parent) = path.parent() {
+        std::fs::create_dir_all(parent)?;
+    }
+    std::fs::write(&path, port.to_string())?;
+    Ok(())
+}
+
 async fn handle_connection(
     stream: tokio::net::UnixStream,
     registry: Registry,
@@ -110,7 +147,7 @@ async fn handle_connection(
     Ok(())
 }
 
-async fn dispatch(req: Request, registry: &Registry) -> Response {
+pub(crate) async fn dispatch(req: Request, registry: &Registry) -> Response {
     match req {
         Request::LaunchApp {
             app_id,

crates/weft-appd/src/ws.rs

@@ -0,0 +1,54 @@
+use futures_util::{SinkExt, StreamExt};
+use tokio::sync::broadcast;
+use tokio_tungstenite::{accept_async, tungstenite::Message};
+
+use crate::{Registry, dispatch, ipc::Request, ipc::Response};
+
+pub async fn handle_ws_connection(
+    stream: tokio::net::TcpStream,
+    registry: Registry,
+    broadcast_rx: broadcast::Receiver<Response>,
+) -> anyhow::Result<()> {
+    let ws_stream = accept_async(stream).await?;
+    let (mut ws_write, mut ws_read) = ws_stream.split();
+    let mut broadcast_rx = broadcast_rx;
+
+    loop {
+        tokio::select! {
+            msg = ws_read.next() => {
+                match msg {
+                    Some(Ok(Message::Text(text))) => {
+                        let req: Request = match serde_json::from_str(&text) {
+                            Ok(r) => r,
+                            Err(e) => {
+                                tracing::warn!(error = %e, "invalid WS request");
+                                continue;
+                            }
+                        };
+                        tracing::debug!(?req, "ws request");
+                        let resp = dispatch(req, &registry).await;
+                        let json = serde_json::to_string(&resp)?;
+                        ws_write.send(Message::Text(json)).await?;
+                    }
+                    Some(Ok(Message::Close(_))) | None => break,
+                    Some(Ok(_)) => {}
+                    Some(Err(e)) => {
+                        tracing::warn!(error = %e, "ws error");
+                        break;
+                    }
+                }
+            }
+            notification = broadcast_rx.recv() => {
+                match notification {
+                    Ok(resp) => {
+                        let json = serde_json::to_string(&resp)?;
+                        ws_write.send(Message::Text(json)).await?;
+                    }
+                    Err(broadcast::error::RecvError::Lagged(_)) => {}
+                    Err(broadcast::error::RecvError::Closed) => break,
+                }
+            }
+        }
+    }
+    Ok(())
+}

infra/shell/system-ui.html

@@ -161,6 +161,99 @@
           launcher.setAttribute('hidden', '');
         }
       });
+
+      var APPD_WS_PORT = window.WEFT_APPD_WS_PORT || 7410;
+      var ws = null;
+      var wsReconnectDelay = 1000;
+
+      function appdConnect() {
+        try {
+          ws = new WebSocket('ws://127.0.0.1:' + APPD_WS_PORT + '/appd');
+        } catch (e) {
+          scheduleReconnect();
+          return;
+        }
+
+        ws.addEventListener('open', function () {
+          wsReconnectDelay = 1000;
+          ws.send(JSON.stringify({ type: 'QUERY_RUNNING' }));
+        });
+
+        ws.addEventListener('message', function (ev) {
+          var msg;
+          try { msg = JSON.parse(ev.data); } catch (e) { return; }
+          handleAppdMessage(msg);
+        });
+
+        ws.addEventListener('close', function () {
+          ws = null;
+          scheduleReconnect();
+        });
+
+        ws.addEventListener('error', function () {
+          ws = null;
+        });
+      }
+
+      function scheduleReconnect() {
+        setTimeout(appdConnect, wsReconnectDelay);
+        wsReconnectDelay = Math.min(wsReconnectDelay * 2, 16000);
+      }
+
+      function handleAppdMessage(msg) {
+        if (msg.type === 'APP_READY') {
+          showNotification('App ready (session ' + msg.session_id + ')');
+        } else if (msg.type === 'APP_STATE') {
+          if (msg.state === 'stopped') {
+            removeTaskbarEntry(msg.session_id);
+          }
+        } else if (msg.type === 'RUNNING_APPS') {
+          msg.session_ids.forEach(function (id) {
+            ensureTaskbarEntry(id);
+          });
+        } else if (msg.type === 'LAUNCH_ACK') {
+          ensureTaskbarEntry(msg.session_id);
+        }
+      }
+
+      function ensureTaskbarEntry(sessionId) {
+        var id = 'task-' + sessionId;
+        if (document.getElementById(id)) { return; }
+        var el = document.createElement('weft-taskbar-app');
+        el.id = id;
+        el.dataset.sessionId = sessionId;
+        el.textContent = '● ' + sessionId;
+        el.style.cssText = 'font-size:12px;color:var(--text-secondary);padding:0 6px;cursor:pointer;';
+        el.title = 'Session ' + sessionId;
+        var taskbar = document.querySelector('weft-taskbar');
+        var clock = document.getElementById('clock');
+        taskbar.insertBefore(el, clock);
+      }
+
+      function removeTaskbarEntry(sessionId) {
+        var el = document.getElementById('task-' + sessionId);
+        if (el) { el.remove(); }
+      }
+
+      function showNotification(text) {
+        var center = document.getElementById('notifications');
+        var note = document.createElement('div');
+        note.textContent = text;
+        note.style.cssText = [
+          'background:var(--surface-bg)',
+          'border:1px solid var(--surface-border)',
+          'border-radius:8px',
+          'padding:10px 14px',
+          'font-size:13px',
+          'color:var(--text-primary)',
+          'pointer-events:auto',
+          'backdrop-filter:blur(20px)',
+        ].join(';');
+        center.appendChild(note);
+        setTimeout(function () { note.remove(); }, 4000);
+      }
+
+      appdConnect();
     }());
   </script>
 </body>