fix(maestro): serialize structured shutdown

Cargo.lock

@@ -1558,6 +1558,7 @@ version = "0.1.0"
 dependencies = [
  "chrono",
  "futures-util",
+ "libc",
  "maestro-protocol",
  "maestro-testing",
  "maestro-tui",

crates/maestro-acp/tests/fake_acp_agent.py

@@ -17,6 +17,8 @@ Environment knobs, all optional:
                             signal SIGTERM
   FAKE_ACP_ECHO_ENV       name of one env var to log at start
   FAKE_ACP_INIT_FAIL=1    answer `initialize` with a JSON-RPC error
+  FAKE_ACP_DELAY_SESSION_NEW_MS=n  wait n milliseconds before answering
+                             `session/new`
   FAKE_ACP_EXIT_AFTER_NEW=1  exit 0 right after answering `session/new`
   FAKE_ACP_EXIT_ON_CANCEL=1  exit 0 on `session/cancel` (default: keep running
                              so the SIGTERM path is exercised)
@@ -36,6 +38,7 @@ import json
 import os
 import signal
 import sys
+import time
 
 LOG = os.environ.get("FAKE_ACP_LOG")
 
@@ -113,6 +116,7 @@ for raw in sys.stdin:
             "authMethods": [],
         }})
     elif method == "session/new":
+        time.sleep(int(os.environ.get("FAKE_ACP_DELAY_SESSION_NEW_MS", "0")) / 1000)
         send({"jsonrpc": "2.0", "id": rid, "result": {"sessionId": session_id}})
         send(chunk("hello from fake"))
         if os.environ.get("FAKE_ACP_EXIT_AFTER_NEW") == "1":

crates/maestro-daemon/src/cli.rs

@@ -122,21 +122,23 @@ async fn run(config_override: Option<PathBuf>) -> Result<(), Box<dyn Error>> {
     // shutdown, and both must reach the adapter children below (#134). The
     // unit's `KillMode=process` signals only the daemon, so nothing else
     // would end them.
-    let shutdown = async {
+    let shutdown_manager = manager.clone();
+    let shutdown = async move {
         let mut sigterm = tokio::signal::unix::signal(tokio::signal::unix::SignalKind::terminate())
             .expect("install SIGTERM handler");
         tokio::select! {
             _ = tokio::signal::ctrl_c() => tracing::info!("ctrl-c received — shutting down"),
             _ = sigterm.recv() => tracing::info!("SIGTERM received — shutting down"),
         }
+        // Axum waits for upgraded WebSockets to drain. Structured children
+        // must be settled before that wait, while the signal path still owns
+        // the shutdown order (#179).
+        shutdown_manager.shutdown().await;
     };
 
     axum::serve(listener, router)
         .tcp_nodelay(true)
         .with_graceful_shutdown(shutdown)
         .await?;
-    // tmux sessions outlive the daemon by design; structured sessions'
-    // adapter children do not (#134).
-    manager.shutdown().await;
     Ok(())
 }

crates/maestro-daemon/src/local_api.rs

@@ -170,6 +170,7 @@ fn session_error_status(code: &str) -> StatusCode {
         // The session outlived its pane: nothing to type into, and nothing
         // the daemon can do about it.
         "not_running" => StatusCode::CONFLICT,
+        "shutting_down" => StatusCode::SERVICE_UNAVAILABLE,
         _ => StatusCode::BAD_GATEWAY,
     }
 }

crates/maestro-daemon/src/session.rs

@@ -7,7 +7,7 @@
 
 use std::collections::{HashMap, HashSet};
 use std::path::PathBuf;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -127,6 +127,8 @@ pub enum SessionError {
     /// a stray keystroke on an attach socket, which is dropped.
     #[error("session is no longer running: {0}")]
     NotRunning(Uuid),
+    #[error("daemon is shutting down")]
+    ShuttingDown,
     /// The kill was refused (#79): the session's worktree holds unsaved work.
     /// Nothing happened — the session keeps running and the tree is untouched,
     /// so it stays the operator's handle on their own unfinished work.
@@ -144,6 +146,7 @@ impl SessionError {
             SessionError::NotFound(_) => "not_found",
             SessionError::InvalidEnv(_) => "invalid_env",
             SessionError::NotRunning(_) => "not_running",
+            SessionError::ShuttingDown => "shutting_down",
             SessionError::KillGuarded(_) => "kill_guarded",
         };
         let unsaved_work = match self {
@@ -195,6 +198,12 @@ struct Inner {
     /// client that reconnects never collides with the registration its
     /// previous socket has not finished releasing.
     next_viewport: AtomicU64,
+    /// Once daemon shutdown starts, it owns structured-session finalization.
+    /// Background passes must not classify those deliberate exits as natural.
+    shutting_down: AtomicBool,
+    /// Serializes structured creation with shutdown so every adapter child is
+    /// either rejected or included in shutdown's final drain.
+    structured_lifecycle: Mutex<()>,
 }
 
 impl SessionManager {
@@ -237,6 +246,8 @@ impl SessionManager {
                 events,
                 viewports: Mutex::new(Viewports::new()),
                 next_viewport: AtomicU64::new(0),
+                shutting_down: AtomicBool::new(false),
+                structured_lifecycle: Mutex::new(()),
             }),
         }
     }
@@ -349,13 +360,18 @@ impl SessionManager {
     /// is on disk after the restart is truthful. tmux sessions are left
     /// alone — surviving a restart is what they are for.
     pub async fn shutdown(&self) {
+        if self.inner.shutting_down.swap(true, Ordering::AcqRel) {
+            return;
+        }
+        let _lifecycle = self.inner.structured_lifecycle.lock().await;
         let children: Vec<(Uuid, Arc<AcpSession>, Option<watch::Receiver<bool>>)> = {
             let sessions = self.inner.sessions.lock().await;
             sessions
                 .iter()
                 .filter_map(|(id, r)| {
-                    r.acp
+                    (r.session.status == SessionStatus::Running)
-                        .clone()
+                        .then_some(())
+                        .and_then(|()| r.acp.clone())
                         .map(|acp| (*id, acp, r.acp_event_pump.clone()))
                 })
                 .collect()
@@ -374,7 +390,7 @@ impl SessionManager {
             .map(wait_for_event_pump);
         futures_util::future::join_all(drains).await;
         for (id, _, _) in children {
-            mark_session_dead(&self.inner, id).await;
+            mark_session_dead_after_shutdown(&self.inner, id).await;
         }
     }
 
@@ -457,6 +473,17 @@ impl SessionManager {
 
     /// Spawn a new session. On success returns the freshly-created `Session`.
     pub async fn create(&self, req: CreateSessionRequest) -> Result<Session, SessionError> {
+        if req.view == SessionView::Structured {
+            let _lifecycle = self.inner.structured_lifecycle.lock().await;
+            if self.inner.shutting_down.load(Ordering::Acquire) {
+                return Err(SessionError::ShuttingDown);
+            }
+            return self.create_inner(req).await;
+        }
+        self.create_inner(req).await
+    }
+
+    async fn create_inner(&self, req: CreateSessionRequest) -> Result<Session, SessionError> {
         let (effective_cwd, worktree_path, worktree_base_repo) = match &req.worktree {
             Some(spec) => {
                 let WorktreeSpec {
@@ -1438,6 +1465,9 @@ async fn probe_worktree(
 /// One pass of the liveness watcher: diff the in-memory session set against
 /// the tmux-reported one, and reap anything we still track but tmux has lost.
 async fn run_liveness_pass(inner: &Arc<Inner>) {
+    if inner.shutting_down.load(Ordering::Acquire) {
+        return;
+    }
     // Snapshot the in-memory ids first; if we own no sessions there is
     // nothing to reap and no reason to spawn a tmux subprocess (this also
     // avoids racing with the very first `new-session` that would otherwise
@@ -1497,6 +1527,9 @@ async fn run_liveness_pass(inner: &Arc<Inner>) {
 /// `SessionUpdated` only when `activity` or `foreground` actually changes — so a
 /// steady state produces no diffs. Runs on the existing liveness tick.
 async fn run_activity_pass(inner: &Arc<Inner>) {
+    if inner.shutting_down.load(Ordering::Acquire) {
+        return;
+    }
     let ids: Vec<Uuid> = {
         let sessions = inner.sessions.lock().await;
         if sessions.is_empty() {
@@ -1539,6 +1572,9 @@ async fn run_activity_pass(inner: &Arc<Inner>) {
 
         let updated = {
             let mut sessions = inner.sessions.lock().await;
+            if inner.shutting_down.load(Ordering::Acquire) {
+                return;
+            }
             let Some(rec) = sessions.get_mut(&id) else {
                 continue;
             };
@@ -1613,6 +1649,9 @@ async fn run_activity_pass(inner: &Arc<Inner>) {
 /// error must not read as "nothing blocks". Like the activity pass, this only
 /// emits `SessionUpdated` when the value actually changed.
 async fn run_blocked_work_pass(inner: &Arc<Inner>) {
+    if inner.shutting_down.load(Ordering::Acquire) {
+        return;
+    }
     let targets: Vec<(Uuid, (PathBuf, PathBuf))> = {
         let sessions = inner.sessions.lock().await;
         sessions
@@ -1640,6 +1679,9 @@ async fn run_blocked_work_pass(inner: &Arc<Inner>) {
         };
         let updated = {
             let mut sessions = inner.sessions.lock().await;
+            if inner.shutting_down.load(Ordering::Acquire) {
+                return;
+            }
             let Some(rec) = sessions.get_mut(&id) else {
                 continue;
             };
@@ -1656,7 +1698,7 @@ async fn run_blocked_work_pass(inner: &Arc<Inner>) {
     }
 }
 
-/// Mark a session whose tmux session has disappeared as [`SessionStatus::Dead`]
+/// Mark a session whose backing process has disappeared as [`SessionStatus::Dead`]
 /// and settle its worktree per the natural-exit rule (#82).
 ///
 /// The record, its [`PtyBridge`] and its sidecar all survive, so a client can
@@ -1668,9 +1710,27 @@ async fn run_blocked_work_pass(inner: &Arc<Inner>) {
 /// alone and stays attached to the dead record for a later forced dismissal
 /// (#81), which leaves it on disk too.
 ///
-/// Dead sessions do not survive a daemon restart: [`SessionManager::recover`]
+/// Terminal sessions that die naturally do not survive a daemon restart:
-/// adopts only what tmux still holds.
+/// [`SessionManager::recover`] adopts only what tmux still holds. Structured
+/// sessions stopped for daemon shutdown retain their sidecars for ACP recovery.
 async fn mark_session_dead(inner: &Arc<Inner>, id: Uuid) {
+    if inner.shutting_down.load(Ordering::Acquire) {
+        return;
+    }
+    mark_session_dead_with_worktree_settlement(inner, id, true).await;
+}
+
+/// A daemon restart terminates ACP children, but it is not a natural adapter
+/// exit: the sidecar is the recovery inventory, including its worktree.
+async fn mark_session_dead_after_shutdown(inner: &Arc<Inner>, id: Uuid) {
+    mark_session_dead_with_worktree_settlement(inner, id, false).await;
+}
+
+async fn mark_session_dead_with_worktree_settlement(
+    inner: &Arc<Inner>,
+    id: Uuid,
+    settle_worktree: bool,
+) {
     let flipped = {
         let mut sessions = inner.sessions.lock().await;
         match sessions.get_mut(&id) {
@@ -1694,17 +1754,19 @@ async fn mark_session_dead(inner: &Arc<Inner>, id: Uuid) {
     };
     tracing::info!(%id, "session process gone — marking dead");
 
-    if let Some(wt) = &worktree {
+    if settle_worktree {
-        if settle_worktree_on_exit(inner, id, wt).await {
+        if let Some(wt) = &worktree {
-            // The tree is settled (removed); a stale "in the way" would
+            if settle_worktree_on_exit(inner, id, wt).await {
-            // describe something the session no longer holds.
+                // The tree is settled (removed); a stale "in the way" would
-            session.blocked_work = None;
+                // describe something the session no longer holds.
-            let mut sessions = inner.sessions.lock().await;
+                session.blocked_work = None;
-            if let Some(record) = sessions.get_mut(&id) {
+                let mut sessions = inner.sessions.lock().await;
-                record.session.worktree = None;
+                if let Some(record) = sessions.get_mut(&id) {
-                record.session.blocked_work = None;
+                    record.session.worktree = None;
-                record.worktree_path = None;
+                    record.session.blocked_work = None;
-                record.worktree_base_repo = None;
+                    record.worktree_path = None;
+                    record.worktree_base_repo = None;
+                }
             }
         }
     }

crates/maestro-daemon/tests/acp.rs

@@ -9,13 +9,15 @@ use std::path::{Path, PathBuf};
 use std::sync::Arc;
 use std::time::{Duration, Instant};
 
-use common::{wait_for_async, DaemonFixture};
+use common::{init_bare_repo, init_repo, push_all_to_origin, wait_for_async, DaemonFixture};
 use maestro_acp::schema::{ContentBlock, SessionUpdate};
 use maestro_acp::{ADAPTER_BIN, INSTALL_COMMAND};
 use maestro_daemon::sidecar::{EventCursor, SidecarStore};
 use maestro_daemon::worktree::WorktreeManager;
 use maestro_daemon::SessionManager;
-use maestro_protocol::{ActivityState, CreateSessionRequest, SessionStatus, SessionView};
+use maestro_protocol::{
+    ActivityState, CreateSessionRequest, SessionStatus, SessionView, WorktreeSpec,
+};
 use tempfile::TempDir;
 
 fn fake_agent() -> PathBuf {
@@ -285,6 +287,76 @@ async fn recovery_loads_the_acp_session_without_duplicating_history() {
     revived.kill(session.id, false).await.expect("kill");
 }
 
+#[tokio::test]
+async fn shutdown_preserves_a_pristine_structured_worktree_for_recovery() {
+    let fx = DaemonFixture::new();
+    let fake = Fake::new();
+    let repo = TempDir::new().unwrap();
+    init_repo(repo.path());
+    let origin = TempDir::new().unwrap();
+    init_bare_repo(origin.path());
+
+    let branch = "feature/restart";
+    let worktree = repo
+        .path()
+        .join("worktrees")
+        .join("feature")
+        .join("restart");
+    let session = fx
+        .manager
+        .create(CreateSessionRequest {
+            view: SessionView::Structured,
+            cwd: repo.path().to_path_buf(),
+            command: "claude".into(),
+            env: fake.env(),
+            metadata: HashMap::new(),
+            worktree: Some(WorktreeSpec {
+                base_repo: repo.path().to_path_buf(),
+                branch: branch.into(),
+                create_branch: true,
+            }),
+        })
+        .await
+        .expect("create");
+    assert_eq!(session.cwd, worktree);
+    push_all_to_origin(repo.path(), origin.path());
+
+    fx.manager.shutdown().await;
+
+    assert!(
+        worktree.is_dir(),
+        "shutdown must not settle a pristine worktree"
+    );
+    let sidecar: maestro_protocol::Session = serde_json::from_slice(
+        &std::fs::read(fx.sidecar_dir().join(format!("{}.json", session.id))).unwrap(),
+    )
+    .unwrap();
+    assert_eq!(
+        sidecar.worktree.as_ref().map(|wt| &wt.path),
+        Some(&worktree)
+    );
+
+    let revived = SessionManager::new(
+        Arc::new(fx.tmux.tmux.clone()),
+        SidecarStore::new(fx.sidecar_dir()),
+        WorktreeManager::new(None),
+        fx.fifo_dir(),
+    );
+    assert_eq!(revived.recover().await.expect("recover"), 1);
+    assert_eq!(
+        revived.status(session.id).await,
+        Some(SessionStatus::Running)
+    );
+    assert!(fake.log().contains("recv session/load"), "{}", fake.log());
+    assert!(worktree.is_dir(), "recovery must retain the worktree");
+
+    revived.kill(session.id, false).await.expect("dismiss");
+    assert!(
+        !worktree.exists(),
+        "operator dismissal still cleans a pristine tree"
+    );
+}
+
 #[tokio::test]
 async fn failed_recovery_cleans_its_fifo() {
     let fx = DaemonFixture::new();
@@ -426,6 +498,50 @@ async fn shutdown_reaps_every_adapter_child() {
     assert_eq!(sidecar.status, SessionStatus::Dead);
 }
 
+#[tokio::test]
+async fn shutdown_waits_for_structured_creation_and_rejects_new_creates() {
+    let fx = DaemonFixture::new();
+    let fake = Fake::new();
+    let cwd = TempDir::new().unwrap();
+    let mut env = fake.env();
+    env.insert("FAKE_ACP_DELAY_SESSION_NEW_MS".into(), "500".into());
+
+    let create_cwd = cwd.path().to_path_buf();
+    let manager = fx.manager.clone();
+    let create = tokio::spawn(async move { manager.create(structured(&create_cwd, env)).await });
+    wait_for_async(Duration::from_secs(5), || async {
+        fake.log().contains("recv session/new")
+    })
+    .await;
+
+    let manager = fx.manager.clone();
+    let shutdown = tokio::spawn(async move { manager.shutdown().await });
+    tokio::time::sleep(Duration::from_millis(50)).await;
+    assert!(
+        !shutdown.is_finished(),
+        "shutdown returned before create finished"
+    );
+
+    let session = create.await.expect("create task").expect("create");
+    let pid = fake.pid();
+    shutdown.await.expect("shutdown task");
+
+    wait_for_exit(pid).await;
+    assert!(fake.log().contains("signal SIGTERM"), "{}", fake.log());
+    assert_eq!(
+        fx.manager.status(session.id).await,
+        Some(SessionStatus::Dead)
+    );
+    assert!(matches!(
+        fx.manager.create(structured(cwd.path(), fake.env())).await,
+        Err(maestro_daemon::SessionError::ShuttingDown)
+    ));
+
+    // A repeated signal must not attempt to terminate the child again.
+    fx.manager.shutdown().await;
+    assert_eq!(fake.log().matches("signal SIGTERM").count(), 1);
+}
+
 #[tokio::test]
 async fn shutdown_drains_final_notifications_to_the_log() {
     let fx = DaemonFixture::new();

crates/maestro-e2e/Cargo.toml

@@ -13,6 +13,7 @@ path = "src/lib.rs"
 [dependencies]
 chrono.workspace = true
 futures-util.workspace = true
+libc.workspace = true
 maestro-protocol = { workspace = true, features = ["client"] }
 maestro-testing.workspace = true
 serde.workspace = true

crates/maestro-e2e/src/daemon.rs

@@ -87,6 +87,14 @@ impl Daemon {
         }
     }
 
+    /// Send the daemon the same SIGTERM systemd uses, without waiting for its
+    /// graceful HTTP shutdown to finish.
+    pub fn send_sigterm(&self) {
+        let child = self.child.as_ref().expect("daemon is running");
+        let result = unsafe { libc::kill(child.id() as libc::pid_t, libc::SIGTERM) };
+        assert_eq!(result, 0, "send SIGTERM to daemon");
+    }
+
     /// Re-spawn the daemon on the same port + state. The previous tmux
     /// server (under `TMUX_TMPDIR`) is left running so `recover()` can adopt
     /// its sessions.

crates/maestro-e2e/tests/e2e.rs

@@ -15,7 +15,7 @@ use std::time::{Duration, Instant};
 use futures_util::{SinkExt, StreamExt};
 use maestro_e2e::util::wait_for_async;
 use maestro_e2e::{Daemon, TestClient};
-use maestro_protocol::{CreateSessionRequest, WorktreeSpec};
+use maestro_protocol::{CreateSessionRequest, SessionStatus, SessionView, WorktreeSpec};
 use tempfile::TempDir;
 use tokio_tungstenite::tungstenite::Message as WsMessage;
 
@@ -36,6 +36,61 @@ fn create_req(cwd: &std::path::Path, command: &str) -> CreateSessionRequest {
     }
 }
 
+struct FakeAcp {
+    _dir: TempDir,
+    env: HashMap<String, String>,
+}
+
+fn fake_acp(log: &std::path::Path) -> FakeAcp {
+    let dir = tempfile::tempdir().expect("fake adapter dir");
+    let adapter = dir.path().join("claude-code-acp");
+    std::fs::copy(
+        concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/../maestro-acp/tests/fake_acp_agent.py"
+        ),
+        &adapter,
+    )
+    .expect("copy fake adapter");
+    let mut permissions = std::fs::metadata(&adapter)
+        .expect("adapter metadata")
+        .permissions();
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::PermissionsExt;
+        permissions.set_mode(0o755);
+    }
+    std::fs::set_permissions(&adapter, permissions).expect("make fake adapter executable");
+    let env = HashMap::from([
+        (
+            "PATH".into(),
+            format!(
+                "{}:{}",
+                dir.path().display(),
+                std::env::var("PATH").unwrap_or_default()
+            ),
+        ),
+        ("FAKE_ACP_LOG".into(), log.to_string_lossy().into_owned()),
+    ]);
+    FakeAcp { _dir: dir, env }
+}
+
+fn fake_acp_pid(log: &std::path::Path) -> Option<u32> {
+    std::fs::read_to_string(log).ok()?.lines().find_map(|line| {
+        line.strip_prefix("start pid=")?
+            .split(' ')
+            .next()?
+            .parse()
+            .ok()
+    })
+}
+
+fn pid_alive(pid: u32) -> bool {
+    std::fs::read_to_string(format!("/proc/{pid}/stat"))
+        .map(|stat| !stat.contains(") Z "))
+        .unwrap_or(false)
+}
+
 /// A worktree spec built through its wire shape. The daemon and clients ship
 /// together (#87 dropped `cleanup_on_kill` from the struct), so the JSON
 /// object carries only the fields the lifecycle actually honours.
@@ -995,6 +1050,66 @@ async fn daemon_restart_recovers_session() {
     client.kill_session(s.id).await.expect("kill");
 }
 
+#[tokio::test(flavor = "multi_thread")]
+async fn sigterm_stops_structured_child_before_events_ws_drains() {
+    let (mut daemon, client) = bring_up().await;
+    let cwd = TempDir::new().unwrap();
+    let log = cwd.path().join("fake-acp.log");
+    let fake = fake_acp(&log);
+    let session = client
+        .spawn_session(&CreateSessionRequest {
+            view: SessionView::Structured,
+            cwd: cwd.path().to_path_buf(),
+            command: "claude".into(),
+            env: fake.env.clone(),
+            metadata: HashMap::new(),
+            worktree: None,
+        })
+        .await
+        .expect("spawn structured session");
+    let ws_url = daemon.client().events_url().expect("events URL");
+    let (_events_ws, _) = tokio_tungstenite::connect_async(ws_url)
+        .await
+        .expect("events WS handshake");
+    wait_for_async("fake ACP starts", Duration::from_secs(5), || {
+        let log = log.clone();
+        async move { fake_acp_pid(&log).is_some() }
+    })
+    .await;
+    let pid = fake_acp_pid(&log).expect("fake ACP pid");
+
+    daemon.send_sigterm();
+
+    wait_for_async(
+        "fake ACP exits after SIGTERM",
+        Duration::from_secs(5),
+        || async { !pid_alive(pid) },
+    )
+    .await;
+    let sidecar_path = daemon
+        .state_dir()
+        .join("sessions")
+        .join(format!("{}.json", session.id));
+    wait_for_async(
+        "dead structured session sidecar",
+        Duration::from_secs(5),
+        || {
+            let sidecar_path = sidecar_path.clone();
+            async move {
+                std::fs::read(&sidecar_path)
+                    .ok()
+                    .and_then(|json| {
+                        serde_json::from_slice::<maestro_protocol::Session>(&json).ok()
+                    })
+                    .is_some_and(|saved| saved.status == SessionStatus::Dead)
+            }
+        },
+    )
+    .await;
+
+    daemon.stop();
+}
+
 #[tokio::test(flavor = "multi_thread")]
 async fn concurrent_spawns_each_get_unique_ids() {
     let (_daemon, client) = bring_up().await;

docs/INSTALL.md

@@ -208,8 +208,10 @@ When the adapter is missing the spawn still creates the session, marked dead
 with the install command above as its activity detail, so the sidebar says
 what to run. The adapter is a child of the daemon: it ends with a `DELETE
 /api/sessions/:id` (`session/cancel`, then `SIGTERM`) and with the daemon
-itself. Terminal sessions keep surviving restarts through tmux; structured
+itself. A daemon restart ends an in-flight structured turn, but preserves its
-ones do not yet.
+worktree, session record, and event-log transcript. The replacement daemon
+starts a new adapter, resumes it with `session/load`, and replays the
+transcript. Terminal sessions keep surviving restarts through tmux.
 
 ## The browser UI