add one shared templated agent policy and name each agent's bao entity after it

nix/host-modules/swarm-bao.nix

@@ -380,6 +380,16 @@ let
   # The agent PKI grant is its only path on that mount: it can ask the one role
   # for a certificate, not write that role or reach the issuer.
 
+  # The identity grants name each agent's login entity after the agent
+  # (`agent_entity.rs`). `sys/auth/cert` carries `sudo` because a plain `read`
+  # of an auth mount is refused, and it is that one mount: it yields the
+  # accessor an entity alias names the mount by. Every identity stanza lists the
+  # request keys it takes, so the grants cannot set an entity's `policies`, which
+  # would attach any policy to a login. The entity and alias names are not
+  # scoped further, by accessor or by entity: an agent's name is not known at
+  # deploy time, so the guard in `agent_entity.rs` (rename only a name the store
+  # generated, never move an alias) is what prevents an identity swap.
+
   # The two `list` paths end in `/`: bao checks a LIST against the directory
   # with a trailing slash, where `+` matches the empty last segment, so a
   # slashless list path loses that request to the `+/matrix/+` and `+/forge/+`
@@ -401,6 +411,41 @@ let
       capabilities = ["list"]
     }
 
+    path "sys/auth/cert" {
+      capabilities = ["read", "sudo"]
+    }
+
+    path "identity/lookup/entity" {
+      capabilities = ["update"]
+      allowed_parameters = {
+        "alias_name" = []
+        "alias_mount_accessor" = []
+      }
+    }
+
+    path "identity/entity/name/+" {
+      capabilities = ["create", "read", "update"]
+      allowed_parameters = {
+        "name" = []
+      }
+    }
+
+    path "identity/entity/id/+" {
+      capabilities = ["update"]
+      allowed_parameters = {
+        "name" = []
+      }
+    }
+
+    path "identity/entity-alias" {
+      capabilities = ["create", "update"]
+      allowed_parameters = {
+        "name" = []
+        "mount_accessor" = []
+        "canonical_id" = []
+      }
+    }
+
     path "${credentialMountPath}/data/swarm/agents/*" {
       capabilities = ["create", "read", "update"]
     }