feat(#343): route container restart through rebuild queue

hive-c0re/src/rebuild_queue.rs

@@ -32,6 +32,10 @@ pub enum QueueKind {
     /// after the lock bump; children run as independent queue entries
     /// grouped under this parent's `id`. `agent` = `"hyperhive"`.
     StartupSweep,
+    /// Stop + start a container without touching config. Fast op (~5-10s).
+    /// Queued so it serialises against in-flight rebuilds for the same
+    /// agent — prevents a restart racing a rebuild mid-flight.
+    Restart,
 }
 
 impl QueueKind {
@@ -42,6 +46,7 @@ impl QueueKind {
             QueueKind::Spawn => "spawn",
             QueueKind::Destroy => "destroy",
             QueueKind::StartupSweep => "startup_sweep",
+            QueueKind::Restart => "restart",
         }
     }
 }
@@ -591,6 +596,15 @@ async fn dispatch(
             // `finish` clears the step label; no explicit clear needed here.
             Ok(())
         }
+        (QueueKind::Restart, _) => {
+            let name = &entry.agent;
+            let _guard = coord.transient_guard(name, crate::coordinator::TransientKind::Restarting);
+            coord.set_queue_step(Some(entry.id), "nixos-container restart");
+            crate::lifecycle::restart(name).await?;
+            coord.kick_agent(name, "container restarted");
+            coord.rescan_containers_and_emit().await;
+            Ok(())
+        }
     }
 }