feat(#2450): collapse the startup sweep into one inline DAG

The boot is now ONE DAG, assembled inline in submit_boot_tree — no boot_root
Noop anchor, no per-agent child DAGs, no display-only parent_id grouping: a
sweep MetaLock root (only when something is stale) that grows one rebuild
subgraph per stale agent into the same DAG (via append_subgraph, previous
commit), plus one Reconcile root per drifted agent (independent — a boot
reconcile needs no lock bump).

- submit_boot_tree builds the DagSpec inline; removed the single-use
  templates::{boot_root, startup_sweep} builders (inlined per the operator's
  "don't force single-use shapes into templates.rs" steer).
- fanout_specs simplified to the meta-update cascade path only — the startup
  sweep no longer fans out child DAGs, so its branch was dead.
- test: append_subgraph_roots_on_emitter_and_rebases_local_deps.

Vestigial after this (deliberately left as follow-ups, flagged in the PR):
NodeKind::Noop is now unconstructed (contained to hive-c0re, removable);
Template::StartupSweep is unconstructed but a hive-sh4re wire type
(frontend-coordinated removal).

hive-c0re/src/job_queue/templates.rs

@@ -216,49 +216,11 @@ pub fn meta_update(
     }
 }
 
-/// 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,
-        source: Source::AutoUpdate,
-        reason,
-        parent_id: None,
-        approval_id: None,
-        inputs: Vec::new(),
-        perm_payload: None,
-        transient: None,
-        nodes: vec![node("hyperhive", NodeKind::Noop, Vec::new())],
-    }
-}
-
-/// 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).
-pub fn startup_sweep(reason: String, stale_agents: Vec<String>) -> DagSpec {
-    DagSpec {
-        template: Template::StartupSweep,
-        source: Source::AutoUpdate,
-        reason,
-        parent_id: None,
-        approval_id: None,
-        inputs: Vec::new(),
-        perm_payload: None,
-        transient: None,
-        nodes: vec![node(
-            "hyperhive",
-            NodeKind::MetaLock {
-                sweep: true,
-                fanout: Some(stale_agents),
-            },
-            Vec::new(),
-        )],
-    }
-}
+// The boot is now assembled inline in `workers/auto_update.rs::submit_boot_tree`
+// as ONE DAG (a sweep `MetaLock` root that grows rebuild subgraphs in-DAG, plus
+// a `Reconcile` root per drifted agent) — no `boot_root` Noop anchor, no
+// `startup_sweep` parent template, no per-agent child DAGs. The old single-use
+// `boot_root` / `startup_sweep` builders were inlined there and removed.
 
 /// Validate a spec before it enters the queue: node ids are dense
 /// (index = id), deps reference existing nodes, and the dep graph is