Function is_enabled 

pub fn is_enabled() -> bool

Whether the mesh is enabled for this node. Opt-in via RYU_MESH_ENABLED (truthy = anything but empty/0/false/no) OR the mesh-enabled pref (seeded into [MESH_PREF_ENABLED]). The env wins when SET — including an explicit RYU_MESH_ENABLED=0, which overrides the pref — so an operator can always force the mesh off; only when the env is unset does the pref decide. Kept in lockstep with the gateway’s tools::mesh_enabled() so the loopback-trust neutralization (B-9) and Core fail-closed gate agree on the same signal.