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