fix(#1643): filter destroyed-agent targets from dashboard schedule view

hive-c0re/src/coordinator.rs

@@ -2,7 +2,7 @@
 //! socket, and the per-agent sockets: the broker, configured `agent_flake`,
 //! and the map of registered agent sockets.
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::{Arc, Mutex};
@@ -512,7 +512,7 @@ impl Coordinator {
     /// after each tick that fires or rearms a row) so the dashboard's
     /// scheduled-prompts tab updates live without polling.
     pub fn emit_schedules_snapshot(self: &Arc<Self>) {
-        let schedules = match self.scheduled_prompts.list() {
+        let mut schedules: Vec<hive_sh4re::WireSchedule> = match self.scheduled_prompts.list() {
             Ok(rows) => rows
                 .into_iter()
                 .map(crate::manager_server::schedule_to_wire_public)
@@ -522,12 +522,34 @@ impl Coordinator {
                 return;
             }
         };
+        // Strip ghost targets (destroyed agents) so the dashboard doesn't
+        // render dead columns. Best-effort: if the roster cache is
+        // momentarily contended we emit unfiltered rather than block this
+        // sync path — the next snapshot / page reload corrects it.
+        if let Some(live) = self.live_container_names_blocking() {
+            crate::manager_server::filter_ghost_schedule_targets(&mut schedules, &live);
+        }
         self.emit_dashboard_event(DashboardEvent::SchedulesChanged {
             seq: self.next_seq(),
             schedules,
         });
     }
 
+    /// Best-effort synchronous snapshot of live container names (the
+    /// logical agent names from the last `nixos-container list` scan).
+    /// Returns `None` when the roster cache lock is momentarily
+    /// contended, so a transient miss is treated as "roster unknown,
+    /// don't filter" rather than hiding live schedule targets. The async
+    /// `containers_snapshot` is the reliable path for request handlers;
+    /// this exists for the sync `emit_schedules_snapshot` SSE emit.
+    #[must_use]
+    pub fn live_container_names_blocking(&self) -> Option<HashSet<String>> {
+        self.last_containers
+            .try_lock()
+            .ok()
+            .map(|m| m.keys().cloned().collect())
+    }
+
     /// Emit a `RemindersChanged` snapshot event. Called from every
     /// reminder mutation site (agent `remind` calls, operator cancel /
     /// retry, and the scheduler after each delivery batch) so the