feat(#2289): push-based server-warning registry with RAII guard

hive-c0re/src/main.rs

@@ -13,8 +13,8 @@ use hive_sh4re::{HostRequest, HostResponse};
 use hive_c0re::coordinator::{Coordinator, HiveEnv, ServeConfig};
 use hive_c0re::{
     agent_sockets, auto_update, broker, client, crash_watch, dashboard, dashboard_events, forge,
-    job_queue, knowledge, matrix, mcp_sockets, migrate, reminder_scheduler,
-    scheduled_prompts_worker, server, socket_server,
+    host_stats, job_queue, knowledge, matrix, mcp_sockets, migrate, reminder_scheduler,
+    scheduled_prompts_worker, server, socket_server, warnings,
 };
 
 #[derive(Parser)]
@@ -340,6 +340,27 @@ async fn cmd_serve(
             }
         }
     });
+    // Disk-pressure watch: raise a `disk_pressure` banner warning while the
+    // host nix store is over threshold and clear it when back under, via the
+    // push-based warnings registry. Replaces the old per-`/api/state`
+    // `statvfs`. ~60s cadence; first tick fires immediately. The held guard
+    // lives for the task's lifetime — dropping it (on shutdown) clears the
+    // banner.
+    let mut disk_shutdown = coord.shutdown_rx();
+    tokio::spawn(async move {
+        let mut disk_guard: Option<warnings::WarningGuard> = None;
+        let interval = std::time::Duration::from_mins(1);
+        loop {
+            host_stats::refresh_disk_warning(&mut disk_guard);
+            tokio::select! {
+                () = tokio::time::sleep(interval) => {}
+                _ = disk_shutdown.changed() => {
+                    tracing::info!("disk-pressure watch: shutdown signal received");
+                    break;
+                }
+            }
+        }
+    });
     // Matrix user sweep: same shape — ensure every container has
     // an account on the local matrix-tuwunel homeserver with an
     // access_token persisted to `<state>/matrix-token`. No-op when