topology: drop the parent field and the hierarchy it fed

`topology.json` was a map of `name -> parent | null`, and that value fed
the whole agent hierarchy: `<parent>` / `<children>` recipient sentinels,
the reparenting API (CLI verb, wire verb, dashboard endpoints, DAG node),
the dashboard tree, the rebuild depth sort, and an unconditional
bind-mount grant giving every agent RW on its direct children's state.

Per the operator's ruling the field goes, and with it all of the above.
The file survives as what remains once the value is gone: the roster of
agent names, which is the set `ManageRootAgent` grants mounts over. It is
now a JSON array; `read` still accepts the old map shape and keeps its
keys, so a hive that upgrades across this does not blank its roster (and
so no capability holder loses its mounts for the length of that window).

Two sites kept their behaviour under a different recipient rather than
losing it. Both addressed `<parent>`, which the broker already resolved to
`operator` for a root agent, and every agent is now what that fallback
called a root:

- the harness's turn-failure / plugin-failure notification
  (`Surface::send_to_parent` -> `send_to_operator`), and
- the send allow-list's always-permitted escape hatch, so an agent with a
  restrictive allow-list still has a way to say it is stuck.

What is NOT preserved, deliberately: an agent with no capability no longer
sees any other agent's dirs. `ManageRootAgent`'s own grant is unchanged --
still every agent in the roster, still state RW + config RO, still no
`harness`.

The dashboard's reparenting control (the M0V3 picker) is deleted with its
CSS. The tree rendering that reads `ContainerView.parent` is left for the
frontend owner -- it degrades to a flat list with the field gone.

hive-c0re/src/job_queue/exec.rs

@@ -60,7 +60,7 @@ pub(super) async fn run_node(
     kind: &NodeKind,
 ) -> (super::JobBuilder, Result<()>) {
     // The agent this node targets rides the payload — empty for the agentless
-    // kinds (`MetaLock`, `Reparent`), which never read it.
+    // kinds (`MetaLock`), which never read it.
     let agent = kind.agent();
     // Every arm is `Result<()>`; the three that grow work declare into `builder`
     // *synchronously*, after their own awaits have finished. Borrowing `&builder`
@@ -120,7 +120,6 @@ pub(super) async fn run_node(
         // takes it directly instead of re-matching the kind behind a `bail!`
         // that could never fire.
         NodeKind::WritePermFile { payload, .. } => run_write_perm_file(coord, agent, payload).await,
-        NodeKind::Reparent { moves } => run_reparent(coord, moves).await,
         NodeKind::MergeVerify { approval_id, .. } => {
             run_merge_verify(coord, *approval_id, id).await
         }
@@ -815,33 +814,6 @@ async fn run_write_perm_file(
     Ok(())
 }
 
-/// Apply the node's `(child, new_parent)` moves as one `META_LOCK`-fused
-/// commit (`Coordinator::reparent_bulk_with_notify`, which already handles
-/// both the single- and bulk-move case, sends the per-agent move
-/// notifications, and rescans + diff-emits the container tree). Runs under
-/// the deploy window (it declares `Resource::MetaWindow`), same reasoning as
-/// `run_write_perm_file`: a topology commit landing inside another node's
-/// staged deploy window would sweep the staged lock into its commit.
-async fn run_reparent(
-    coord: &Arc<Coordinator>,
-    moves: &[(hive_types::Ident, Option<hive_types::Ident>)],
-) -> Result<()> {
-    let refs: Vec<(&str, Option<&str>)> = moves
-        .iter()
-        .map(|(child, parent)| {
-            (
-                child.as_str(),
-                parent.as_ref().map(hive_types::Ident::as_str),
-            )
-        })
-        .collect();
-    coord
-        .reparent_bulk_with_notify(&refs)
-        .await
-        .map_err(|e| anyhow::anyhow!(e))?;
-    Ok(())
-}
-
 /// Deploy phase 1 — drift gate, fetch, eval-verify. Mutates nothing, so a
 /// failure here cancel-cascades the rest of the subtree with the forge and the
 /// applied repo exactly as they were.
@@ -890,7 +862,9 @@ async fn run_deploy_tail(
 /// flake affects — the fan-out set for `MetaUpdate` DAGs. Empty
 /// `inputs` or any input under `hyperhive` → every container;
 /// otherwise just the agents named by `agent-<name>` inputs.
-/// Topology-sorted so parents rebuild before their children.
+/// Sorted by name — #4472 removed the parent field the old depth sort
+/// keyed on, and with every agent a root that sort already reduced to
+/// this.
 ///
 /// `inputs` is the caller-supplied flake-input-name list (the dashboard's
 /// `POST /api/meta-update` form field, operator-supplied but not
@@ -918,8 +892,7 @@ pub async fn meta_update_cascade_agents(inputs: &[String]) -> Vec<String> {
     } else {
         touched_agents
     };
-    let topo = crate::topology::read();
-    crate::auto_update::topology_sort(&mut names, &topo);
+    names.sort();
     names
 }