Function default_gate_for 

pub fn default_gate_for(_level: LoopLevel) -> Arc<dyn HumanGate>

The gate a level implies when the caller doesn’t specify one.

L1 and L2 both default to AlwaysEscalate — L1 because it only ever reports, L2 because a human must gate every change. L3 has no safe default (an unattended loop needs an explicit allowlist), so it also defaults to AlwaysEscalate until the caller supplies an AllowlistGate via LoopEngine::with_gate.