feat(#2392): group boot sweep + reconciles under one boot dag

hive-c0re/src/job_queue/templates.rs

@@ -281,6 +281,30 @@ pub fn meta_update(
 /// Boot-time sweep parent: bump meta's hyperhive input (non-fatal),
 /// then fan out `Rebuild` children for the precomputed stale agent
 /// list (topology-sorted by the caller).
+/// Boot-time root anchor DAG: a single [`NodeKind::Noop`] node that groups
+/// this boot's `StartupSweep` + per-agent `Reconcile` child DAGs (linked via
+/// `parent_id`) into one tree so the dashboard renders the boot as one entry.
+/// Holds no lease and does no work — the children it anchors still run
+/// concurrently. `auto_update::run` submits it first (when there's any boot
+/// work), then parents the sweep + reconciles onto its id.
+pub fn boot_root(reason: String) -> DagSpec {
+    DagSpec {
+        template: Template::Boot,
+        agent: "hyperhive".to_owned(),
+        source: Source::AutoUpdate,
+        reason,
+        parent_id: None,
+        approval_id: None,
+        inputs: Vec::new(),
+        perm_payload: None,
+        transient: None,
+        nodes: vec![NodeSpec {
+            kind: NodeKind::Noop,
+            deps: Vec::new(),
+        }],
+    }
+}
+
 pub fn startup_sweep(reason: String, stale_agents: Vec<String>) -> DagSpec {
     DagSpec {
         template: Template::StartupSweep,