job_queue: add NodeKind::Reparent (topology moves as a queue node, #2719)

hive-c0re/src/job_queue/templates.rs

@@ -22,6 +22,7 @@
 //! spawn(a):          Provision(a) → Create(a) → WriteDropin(a) → Reconcile(a)  [wanted=Up at approve]
 //! perm-change(a):    WritePermFile(a) → «rebuild subgraph»
 //! meta-update(inp):  MetaLock(inp) →«in-DAG rebuild subgraph per affected a»
+//! reparent(moves):   Reparent(moves)  [no rebuild — topology.json is read live]
 //! ```
 //!
 //! For the dynamic power-op shapes (`stop` / `start` / `restart`, built from
@@ -341,6 +342,47 @@ pub fn meta_update(
     }
 }
 
+/// Topology move(s) as a single-node DAG. `moves` is `(child, new_parent)`
+/// pairs — len 1 for `set-parent`, len N for `set-parent-bulk`, applied
+/// uniformly by the one [`NodeKind::Reparent`] node (which holds the global
+/// meta window for its duration, same precedent as [`NodeKind::WritePermFile`]).
+/// No rebuild subgraph: `topology.json` is read live by every consumer
+/// (dashboard tree, `<parent>`/`<children>` sentinel routing, permission
+/// checks), so a parent move needs no container rebuild to take effect.
+/// No transient pill either — the node is agentless (no lease to hang one
+/// off of) and near-instant.
+///
+/// Rides `Template::MetaUpdate` rather than a dedicated variant because
+/// `Template` is being removed and nothing should dispatch on it — a fresh
+/// variant would just be more surface to delete later. `Template` is already
+/// internal-only (not on `DagView`'s wire shape — the dashboard derives its
+/// label from `nodes`), so the choice of stand-in variant only affects
+/// `terminal_hook` dispatch (`MetaUpdate` resolves to `None`, same as a
+/// dedicated variant would) and the per-template history-retention bucket —
+/// both cosmetic. Swap this to whatever the eventual node-kind-derived
+/// dispatch lands with, whenever it lands.
+#[allow(
+    dead_code,
+    reason = "landed ahead of the server.rs/dashboard::topology call-site swap, pending an \
+               answer on whether that swap should be synchronous or fire-and-forget — \
+               exercised today by job_queue::tests and submit::reparent"
+)]
+pub fn reparent(
+    moves: Vec<(hive_types::Ident, Option<hive_types::Ident>)>,
+    source: Source,
+    reason: String,
+) -> DagSpec {
+    DagSpec {
+        template: Template::MetaUpdate,
+        source,
+        reason,
+        approval_id: None,
+        inputs: Vec::new(),
+        transient: None,
+        nodes: vec![node(NodeKind::Reparent { moves }, Vec::new())],
+    }
+}
+
 // The boot is assembled inline in `workers/auto_update.rs::submit_boot_tree`
 // as ONE `Boot` DAG (a sweep `MetaLock` root that grows rebuild subgraphs
 // in-DAG, plus a `Reconcile` root per drifted agent) — no anchor node and no