A3k finding 2: distribution reads its caller list as mesh-config resolves it, not from an environment nothing renders

The node-engine fills ${config:} only in files, unit names, owners and groups, never in a
process's environment, so MESH_CONFIG_CALLERS was never set and design 51's defaults always held.
The tools bundle now reads `callers` through stdio.Config on each call (holder.ConfiguredCallers,
Verbs.WithCallers per call); the program, which has no runtime resolving config, asks its own
tools bundle's new registry_callers on each wake of the windows (manifest invokes). The
environment variable is gone.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

modules/distribution/module.json

@@ -43,6 +43,7 @@
     }
   ],
   "tools": [
+    "registry_callers",
     "registry_direct_writes",
     "registry_health",
     "registry_holds",
@@ -50,6 +51,7 @@
     "registry_old_name"
   ],
   "invokes": [
+    "distribution.registry_callers",
     "mesh-delivery-builder.builder_versions",
     "mesh-delivery-view.node_haves",
     "seat:node-engine.manifest-reads"
@@ -199,8 +201,7 @@
       "env": {
         "MESH_BROKER_FILE": "/var/lib/mesh/registry/broker",
         "MESH_REGISTRY_LOOPBACK": "http://127.0.0.1:5001",
-        "MESH_REGISTRY_LISTEN": ":5000",
-        "MESH_CONFIG_CALLERS": "${config:callers}"
+        "MESH_REGISTRY_LISTEN": ":5000"
       },
       "user": "distribution",
       "health": {