docs: retire the agent hierarchy from every page that described it

The topology doc keeps its filename and its second half (manager
special-casing, harness unit shape) — both are cross-referenced from
other pages and neither is about the parent field. Its first half is
rewritten: what topology.json is now, and a table of what the removal
took with it, so a reader who finds `<parent>` or `set-parent` in an old
issue thread learns it went away rather than moved.

The dashboard's tree-rendering section is marked dormant rather than
deleted: the walk is still in swarm.js and retiring it is the frontend
owner's call.

nix/agent-modules/agent-service.nix

@@ -151,9 +151,9 @@ in
       Place the file inside the agent's bind-mounted **harness** dir (e.g.
       `/agents/<name>/harness/openrouter.env`, `$HYPERHIVE_HARNESS_DIR`),
       not `state/` — `harness/` survives container rebuilds exactly like
-      `state/` does, but is never bind-mounted into a parent agent's
-      container (unlike `state/`, which a parent gets read-write for child
-      recovery — see `docs/agent-lifecycle/persistence.md`'s "Parent access to child
+      `state/` does, but is never bind-mounted into another agent's
+      container (unlike `state/`, which a `ManageRootAgent` holder gets
+      read-write for recovery — see `docs/agent-lifecycle/persistence.md`'s "Cross-agent access to
       state"), so this credential is reachable by nothing but this agent
       and the host. Permissions should be `0600`, owned by the agent's
       unix user. Loaded with a leading `-` (optional `EnvironmentFile`),

nix/agent-modules/user.nix

@@ -183,20 +183,21 @@ in
       mkdir -p "$(dirname "$marker")"
       : > "$marker"
       # Scope state + harness chowns to THIS container's own dirs only.
-      # The glob `/agents/*/state` also matches child-agent state dirs that
-      # are bind-mounted into parent containers, which would clobber the
-      # ownership those dirs' own activation scripts set — producing
-      # intermittent EACCES for the child agent's harness between a parent
-      # rebuild and the child's next activation. Config dirs are kept broad
-      # because the parent legitimately owns child proposed-config repos.
+      # The glob `/agents/*/state` also matches other agents' state dirs
+      # bind-mounted into a `ManageRootAgent` holder's container, which
+      # would clobber the ownership those dirs' own activation scripts set
+      # — producing intermittent EACCES for that agent's harness between
+      # the holder's rebuild and its own next activation. Config dirs are
+      # kept broad because the holder legitimately owns the proposed-config
+      # repos it edits.
       if [ -d "/agents/$userName/state" ]; then
         chown -hR "$userName:$userName" "/agents/$userName/state" 2>/dev/null || true
       fi
       if [ -d "/agents/$userName/harness" ]; then
         chown -hR "$userName:$userName" "/agents/$userName/harness" 2>/dev/null || true
       fi
-      # The proposed-config repo is RW-mounted into the editing (parent/
-      # manager) agent and owned by it; hive-c0re only pulls from it. Heal
+      # The proposed-config repo is RW-mounted into the editing agent and
+      # owned by it; hive-c0re only pulls from it. Heal
       # it to this user too — same as state/harness. In an agent's own
       # container its config is RO-mounted, so the chown there just fails
       # harmlessly (|| true).

nix/reserved-names.nix

@@ -60,11 +60,7 @@
   # against hive names, in `swarm-otel.nix`'s own `reservedOwners`.
   "swarm"
 ]
-# Deliberately absent, and both are load-bearing omissions:
-#
-#   `<parent>` / `<children>` — routing recipients the ident charset already
-#   rejects, so no name can ever equal them; listing them would imply a guard
-#   that never fires.
+# Deliberately absent, and it is a load-bearing omission:
 #
 #   `ruth` — a real agent, not a literal. A second agent wanting that name is a
 #   name that is TAKEN, which the roster answers, not this list.