Function trace_on 

pub fn trace_on() -> bool

ATLAS_GLM_ROUTE_TRACE=1 — emit one line per reduce site per layer per token carrying the router’s selected GLOBAL expert ids and the measured rendezvous (arrival-skew) time.

The router is REPLICATED and bit-identical on every rank, so rank 0’s ids are the whole picture: any static ownership map can be scored offline from this one trace without a second run. Costly (one log line per MoE layer per token) — trace, then turn it off.