diff --git a/ui/src/pages/TerminalPage.tsx b/ui/src/pages/TerminalPage.tsx
index 29182c2..0ee4427 100644
--- a/ui/src/pages/TerminalPage.tsx
+++ b/ui/src/pages/TerminalPage.tsx
@@ -576,7 +576,10 @@ export function TerminalPage({
     });
     resizeObserver.observe(hostRef.current);
     void restoreTerminalSession();
+    let refreshInFlight = false;
     const refreshSessions = () => {
+      if (refreshInFlight) return;
+      refreshInFlight = true;
       void listTerminals()
         .then((listed) => {
           if (!cancelled) {
@@ -588,11 +591,13 @@ export function TerminalPage({
         .catch(() => {
           // The attached terminal transport remains authoritative while a
           // background list refresh is temporarily unavailable.
+        })
+        .finally(() => {
+          refreshInFlight = false;
         });
     };
     refreshSessionsRef.current = refreshSessions;
-    // Session lifecycle only changes at connect/disconnect moments or when the
-    // operator returns to the tab; refresh on those instead of polling.
+    const refreshTimer = window.setInterval(refreshSessions, 15_000);
     window.addEventListener("focus", refreshSessions);
 
     return () => {
@@ -600,6 +605,7 @@ export function TerminalPage({
       input.dispose();
       titleChange.dispose();
       resizeObserver.disconnect();
+      window.clearInterval(refreshTimer);
       window.removeEventListener("focus", refreshSessions);
       refreshSessionsRef.current = () => {};
       window.cancelAnimationFrame(resizeFrame);
diff --git a/wakey-agent/src/terminal.rs b/wakey-agent/src/terminal.rs
index df2802d..619c24b 100644
--- a/wakey-agent/src/terminal.rs
+++ b/wakey-agent/src/terminal.rs
@@ -522,7 +522,7 @@ async fn run_terminal_relay(relay: RelayConnection) -> Result<()> {
     let (stream, _) = tokio_tungstenite::connect_async(ws_url.as_str())
         .await
         .context("failed to connect terminal relay websocket")?;
-    let (mut sink, mut source) = stream.split();
+    let (mut sink, source) = stream.split();
     send_json(
         &mut sink,
         &TerminalAgentHandshake::Auth {
@@ -541,40 +541,61 @@ async fn run_terminal_relay(relay: RelayConnection) -> Result<()> {
         .await
         .map_err(|_| anyhow::anyhow!("terminal worker stopped"))?;
 
-    let mut output = relay.output_rx;
+    relay_loop(source, sink, relay.input, relay.generation, relay.output_rx).await
+}
+
+async fn relay_loop<S, St>(
+    mut source: St,
+    mut sink: S,
+    input: mpsc::Sender<RelayInput>,
+    generation: u64,
+    mut output: mpsc::Receiver<Message>,
+) -> Result<()>
+where
+    S: futures_util::Sink<Message, Error = tokio_tungstenite::tungstenite::Error> + Unpin,
+    St: futures_util::Stream<
+            Item = std::result::Result<Message, tokio_tungstenite::tungstenite::Error>,
+        > + Unpin,
+{
+    let mut worker_stopped = false;
+    let mut worker_stop_deadline: Option<tokio::time::Instant> = None;
+    // Reserve at most one control so a full worker queue cannot block output.
+    let mut pending_input = None;
+    let mut close_after_input = false;
     loop {
         tokio::select! {
             biased;
-            incoming = source.next() => {
+            _ = async {
+                match worker_stop_deadline {
+                    Some(deadline) => tokio::time::sleep_until(deadline).await,
+                    None => std::future::pending().await,
+                }
+            } => break,
+            incoming = source.next(), if !worker_stopped && pending_input.is_none() => {
                 let Some(message) = incoming else { break; };
                 match message.context("terminal relay websocket receive failed")? {
                     Message::Binary(bytes) => {
-                        relay.input.send(RelayInput::Binary {
-                            generation: relay.generation,
+                        pending_input = Some(RelayInput::Binary {
+                            generation,
                             bytes: bytes.to_vec(),
-                        }).await.map_err(|_| anyhow::anyhow!("terminal worker stopped"))?;
+                        });
                     }
                     Message::Text(text) => match serde_json::from_str::<TerminalControl>(&text)
                         .context("invalid terminal control frame")?
                     {
                         TerminalControl::Resize { rows, cols } => {
-                            relay.input.send(RelayInput::Resize {
-                                generation: relay.generation,
+                            pending_input = Some(RelayInput::Resize {
+                                generation,
                                 rows,
                                 cols,
-                            }).await
-                                .map_err(|_| anyhow::anyhow!("terminal worker stopped"))?;
+                            });
                         }
                         TerminalControl::Snapshot => {
-                            relay.input.send(RelayInput::Snapshot {
-                                generation: relay.generation,
-                            }).await.map_err(|_| anyhow::anyhow!("terminal worker stopped"))?;
+                            pending_input = Some(RelayInput::Snapshot { generation });
                         }
                         TerminalControl::Close => {
-                            let _ = relay.input.send(RelayInput::Close {
-                                generation: relay.generation,
-                            }).await;
-                            break;
+                            pending_input = Some(RelayInput::Close { generation });
+                            close_after_input = true;
                         }
                         _ => anyhow::bail!("terminal control frame has invalid direction"),
                     },
@@ -586,9 +607,32 @@ async fn run_terminal_relay(relay: RelayConnection) -> Result<()> {
                     Message::Frame(_) => {}
                 }
             }
+            permit = input.reserve(), if !worker_stopped && pending_input.is_some() => {
+                match permit {
+                    Ok(permit) => {
+                        permit.send(pending_input.take().expect("pending terminal input"));
+                        if close_after_input {
+                            break;
+                        }
+                    }
+                    Err(_) => {
+                        worker_stopped = true;
+                        pending_input = None;
+                        worker_stop_deadline =
+                            Some(tokio::time::Instant::now() + PTY_EXIT_DRAIN_TIMEOUT);
+                    }
+                }
+            }
             outgoing = output.recv() => {
                 let Some(message) = outgoing else { break; };
-                sink.send(message).await.context("failed to send terminal relay output")?;
+                if let Some(deadline) = worker_stop_deadline {
+                    tokio::time::timeout_at(deadline, sink.send(message))
+                        .await
+                        .context("terminal relay output drain timed out")?
+                        .context("failed to send terminal relay output")?;
+                } else {
+                    sink.send(message).await.context("failed to send terminal relay output")?;
+                }
             }
         }
     }
@@ -871,6 +915,58 @@ mod tests {
         }
     }
 
+    #[tokio::test]
+    async fn relay_drains_final_output_after_worker_stops_during_concurrent_controls() {
+        let (input, input_rx) = mpsc::channel(RELAY_INPUT_QUEUE);
+        drop(input_rx);
+        let (output_tx, output_rx) = mpsc::channel(RELAY_OUTPUT_QUEUE);
+        output_tx
+            .send(Message::Binary(vec![1, 2, 3].into()))
+            .await
+            .expect("live output queues");
+        let exit_frame = serde_json::to_string(&TerminalControl::Exited { exit_code: Some(0) })
+            .expect("exit frame encodes");
+        output_tx
+            .send(Message::Text(exit_frame.clone().into()))
+            .await
+            .expect("exit output queues");
+        drop(output_tx);
+
+        let source = futures_util::stream::iter([
+            Ok(Message::Binary(vec![4].into())),
+            Ok(Message::Text(
+                serde_json::to_string(&TerminalControl::Resize {
+                    rows: 30,
+                    cols: 100,
+                })
+                .expect("resize encodes")
+                .into(),
+            )),
+            Ok(Message::Text(
+                serde_json::to_string(&TerminalControl::Snapshot)
+                    .expect("snapshot encodes")
+                    .into(),
+            )),
+        ]);
+        let delivered = Arc::new(Mutex::new(Vec::new()));
+        let sink = futures_util::sink::unfold(delivered.clone(), |delivered, frame| async move {
+            delivered.lock().expect("delivered frames").push(frame);
+            Ok::<_, tokio_tungstenite::tungstenite::Error>(delivered)
+        });
+
+        relay_loop(source, Box::pin(sink), input, 7, output_rx)
+            .await
+            .expect("relay drains after worker completion");
+
+        let delivered = delivered.lock().expect("delivered frames");
+        assert_eq!(delivered.len(), 2);
+        assert_eq!(delivered[0].clone().into_data(), vec![1, 2, 3]);
+        let Message::Text(exit) = &delivered[1] else {
+            panic!("exit control should follow final bytes");
+        };
+        assert_eq!(exit.as_str(), exit_frame);
+    }
+
     #[test]
     fn open_rejects_invalid_initial_size_before_spawning() {
         let mut config = crate::config::DEFAULT_CONFIG.clone();
diff --git a/wakey-control-plane/src/api/alerts.rs b/wakey-control-plane/src/api/alerts.rs
index cd04d7d..4a2c6ac 100644
--- a/wakey-control-plane/src/api/alerts.rs
+++ b/wakey-control-plane/src/api/alerts.rs
@@ -35,6 +35,7 @@ pub struct AlertHistoryQuery {
 }
 
 #[derive(Debug, Clone, Deserialize)]
+#[serde(default)]
 pub struct AlertRuleConfig {
     pub lookback_seconds: Option<u64>,
     pub timeout_threshold: Option<u64>,
@@ -53,6 +54,45 @@ impl Default for AlertRuleConfig {
     }
 }
 
+impl AlertRuleConfig {
+    fn validate(&self) -> Result<(), ApiError> {
+        let defaults = Self::default();
+        let overrides = [
+            (
+                "lookback_seconds",
+                self.lookback_seconds,
+                defaults.lookback_seconds,
+            ),
+            (
+                "timeout_threshold",
+                self.timeout_threshold,
+                defaults.timeout_threshold,
+            ),
+            (
+                "auth_rejected_threshold",
+                self.auth_rejected_threshold,
+                defaults.auth_rejected_threshold,
+            ),
+            (
+                "enroll_rejected_threshold",
+                self.enroll_rejected_threshold,
+                defaults.enroll_rejected_threshold,
+            ),
+        ];
+        if let Some((field, _, _)) = overrides
+            .into_iter()
+            .find(|(_, requested, default)| requested.is_some() && requested != default)
+        {
+            return Err(ApiError::new(
+                StatusCode::BAD_REQUEST,
+                "unsupported_alert_override",
+                format!("custom alert {field} is not supported; omit it or use its default value"),
+            ));
+        }
+        Ok(())
+    }
+}
+
 #[derive(Clone, Default)]
 pub struct AlertsSnapshot {
     pub ts_unix: u64,
@@ -67,8 +107,17 @@ pub struct AlertsHub {
     tx: broadcast::Sender<String>,
     latest_payload: Arc<RwLock<Option<String>>>,
     latest_alerts: Arc<RwLock<Vec<AlertState>>>,
+    evaluator_status: Arc<RwLock<EvaluatorStatus>>,
 }
 
+#[derive(Default)]
+struct EvaluatorStatus {
+    last_success_unix: Option<u64>,
+    failure: Option<String>,
+}
+
+const ALERT_SNAPSHOT_MAX_AGE_SECS: u64 = 15;
+
 impl Default for AlertsHub {
     fn default() -> Self {
         Self::new()
@@ -82,6 +131,7 @@ impl AlertsHub {
             tx,
             latest_payload: Arc::new(RwLock::new(None)),
             latest_alerts: Arc::new(RwLock::new(Vec::new())),
+            evaluator_status: Arc::new(RwLock::new(EvaluatorStatus::default())),
         }
     }
 
@@ -97,6 +147,22 @@ impl AlertsHub {
         self.latest_payload.read().await.clone()
     }
 
+    async fn mark_unavailable(&self, reason: impl Into<String>) {
+        self.evaluator_status.write().await.failure = Some(reason.into());
+    }
+
+    async fn unavailable_reason(&self) -> Option<String> {
+        let status = self.evaluator_status.read().await;
+        if let Some(failure) = &status.failure {
+            return Some(failure.clone());
+        }
+        match status.last_success_unix {
+            Some(ts) if now_unix().saturating_sub(ts) <= ALERT_SNAPSHOT_MAX_AGE_SECS => None,
+            Some(_) => Some("alert evaluator snapshot is stale".into()),
+            None => Some("alert evaluator has not produced a snapshot yet".into()),
+        }
+    }
+
     pub async fn publish(&self, snapshot: AlertsSnapshot) {
         let payload = serde_json::json!({
             "type": "alerts_snapshot",
@@ -110,6 +176,10 @@ impl AlertsHub {
         };
         *self.latest_alerts.write().await = snapshot.alerts;
         *self.latest_payload.write().await = Some(encoded.clone());
+        let mut status = self.evaluator_status.write().await;
+        status.last_success_unix = Some(snapshot.ts_unix);
+        status.failure = None;
+        drop(status);
         let _ = self.tx.send(encoded);
     }
 }
@@ -127,6 +197,7 @@ pub async fn run_alert_evaluator(state: AppState) {
             Ok(alerts) => alerts,
             Err(err) => {
                 warn!(code = %err.code, "failed to evaluate alerts in background task");
+                state.alerts.mark_unavailable(err.message.clone()).await;
                 continue;
             }
         };
@@ -154,7 +225,18 @@ pub async fn run_alert_evaluator(state: AppState) {
     }
 }
 
-pub async fn active_alerts(State(state): State<AppState>) -> Result<impl IntoResponse, ApiError> {
+pub async fn active_alerts(
+    State(state): State<AppState>,
+    Query(config): Query<AlertRuleConfig>,
+) -> Result<impl IntoResponse, ApiError> {
+    config.validate()?;
+    if let Some(reason) = state.alerts.unavailable_reason().await {
+        return Err(ApiError::new(
+            StatusCode::SERVICE_UNAVAILABLE,
+            "alerts_unavailable",
+            reason,
+        ));
+    }
     let alerts = state.alerts.latest_alerts().await;
     Ok((StatusCode::OK, Json(alerts)))
 }
@@ -426,9 +508,11 @@ fn now_unix() -> u64 {
 mod tests {
     use std::collections::HashSet;
 
+    use axum::http::StatusCode;
+
     use crate::state::AuditEvent;
 
-    use super::{AlertBuildContext, build_alerts};
+    use super::{AlertBuildContext, AlertRuleConfig, AlertsHub, AlertsSnapshot, build_alerts};
 
     fn event(agent_id: Option<&str>, event_type: &str, outcome: &str, ts_unix: u64) -> AuditEvent {
         AuditEvent {
@@ -517,4 +601,81 @@ mod tests {
                 .any(|a| a.kind == "enroll_reject_spike" && a.agent_id.is_none())
         );
     }
+
+    #[test]
+    fn alert_rule_config_accepts_omitted_and_default_values() {
+        AlertRuleConfig::default().validate().unwrap();
+        AlertRuleConfig {
+            lookback_seconds: None,
+            timeout_threshold: None,
+            auth_rejected_threshold: None,
+            enroll_rejected_threshold: None,
+        }
+        .validate()
+        .unwrap();
+    }
+
+    #[test]
+    fn alert_rule_config_rejects_custom_overrides() {
+        let configs = [
+            AlertRuleConfig {
+                lookback_seconds: Some(300),
+                ..Default::default()
+            },
+            AlertRuleConfig {
+                timeout_threshold: Some(4),
+                ..Default::default()
+            },
+            AlertRuleConfig {
+                auth_rejected_threshold: Some(4),
+                ..Default::default()
+            },
+            AlertRuleConfig {
+                enroll_rejected_threshold: Some(6),
+                ..Default::default()
+            },
+        ];
+
+        for config in configs {
+            let error = config.validate().unwrap_err();
+            assert_eq!(error.status, StatusCode::BAD_REQUEST);
+            assert_eq!(error.code, "unsupported_alert_override");
+            assert!(error.message.contains("not supported"));
+        }
+    }
+
+    #[tokio::test]
+    async fn alert_hub_reports_initial_failure_and_recovers_on_snapshot() {
+        let hub = AlertsHub::new();
+        assert!(hub.unavailable_reason().await.is_some());
+
+        hub.mark_unavailable("store query failed").await;
+        assert_eq!(
+            hub.unavailable_reason().await.as_deref(),
+            Some("store query failed")
+        );
+
+        hub.publish(AlertsSnapshot {
+            ts_unix: super::now_unix(),
+            alerts: Vec::new(),
+            recent_transitions: Vec::new(),
+        })
+        .await;
+        assert_eq!(hub.unavailable_reason().await, None);
+    }
+
+    #[tokio::test]
+    async fn alert_hub_rejects_stale_snapshots() {
+        let hub = AlertsHub::new();
+        hub.publish(AlertsSnapshot {
+            ts_unix: 0,
+            alerts: Vec::new(),
+            recent_transitions: Vec::new(),
+        })
+        .await;
+        assert_eq!(
+            hub.unavailable_reason().await.as_deref(),
+            Some("alert evaluator snapshot is stale")
+        );
+    }
 }
diff --git a/wakey-control-plane/src/api/control/fleet/mod.rs b/wakey-control-plane/src/api/control/fleet/mod.rs
index e0bace1..fecfc8c 100644
--- a/wakey-control-plane/src/api/control/fleet/mod.rs
+++ b/wakey-control-plane/src/api/control/fleet/mod.rs
@@ -27,7 +27,6 @@ use types::{
     RefreshFleetDevicesResponse, WakeFleetDeviceRequest, WakeFleetDeviceResponse,
 };
 
-const MAX_REFRESH_AGENTS: usize = 128;
 const REFRESH_CONCURRENCY: usize = 8;
 
 pub async fn list_fleet_devices(
@@ -51,22 +50,13 @@ pub async fn refresh_fleet_devices(
     State(state): State<AppState>,
     Json(req): Json<RefreshFleetDevicesRequest>,
 ) -> Result<impl IntoResponse, ApiError> {
-    let mut agent_ids = if req.agent_ids.is_empty() {
+    let agent_ids = if req.agent_ids.is_empty() {
         let sessions = state.sessions.read().await;
         sessions.keys().cloned().collect::<Vec<_>>()
     } else {
         req.agent_ids.clone()
     };
-    agent_ids.sort();
-    agent_ids.dedup();
-    if agent_ids.len() > MAX_REFRESH_AGENTS {
-        warn!(
-            requested = agent_ids.len(),
-            capped = MAX_REFRESH_AGENTS,
-            "capping fleet refresh agent count"
-        );
-        agent_ids.truncate(MAX_REFRESH_AGENTS);
-    }
+    let agent_ids = normalize_refresh_agent_ids(agent_ids);
 
     let results = futures_util::stream::iter(agent_ids.into_iter().map(|agent_id| {
         let state = state.clone();
@@ -105,6 +95,12 @@ pub async fn refresh_fleet_devices(
     ))
 }
 
+fn normalize_refresh_agent_ids(mut agent_ids: Vec<String>) -> Vec<String> {
+    agent_ids.sort();
+    agent_ids.dedup();
+    agent_ids
+}
+
 async fn refresh_fleet_agent_result(
     state: &AppState,
     agent_id: &str,
diff --git a/wakey-control-plane/src/api/control/fleet/tests.rs b/wakey-control-plane/src/api/control/fleet/tests.rs
index a611de8..c3dd62e 100644
--- a/wakey-control-plane/src/api/control/fleet/tests.rs
+++ b/wakey-control-plane/src/api/control/fleet/tests.rs
@@ -8,9 +8,23 @@ use super::build::{
     AgentRuntimeStatus, FleetBuildContext, build_fleet_devices, filter_fleet_devices,
     known_device_summary,
 };
+use super::normalize_refresh_agent_ids;
 use super::types::ListFleetDevicesQuery;
 use crate::state::{AgentDeviceRow, AgentDeviceWithChildren, DeviceIdentifier, KnownDevice};
 
+#[test]
+fn refresh_agent_selection_keeps_all_agents_beyond_previous_cap() {
+    let ids = (0..140)
+        .map(|index| format!("agent-{index:03}"))
+        .collect::<Vec<_>>();
+
+    let selected = normalize_refresh_agent_ids(ids);
+
+    assert_eq!(selected.len(), 140);
+    assert_eq!(selected.first().map(String::as_str), Some("agent-000"));
+    assert_eq!(selected.last().map(String::as_str), Some("agent-139"));
+}
+
 fn context(connected: &[&str]) -> FleetBuildContext {
     FleetBuildContext {
         agent_status: connected