Function shared_side 

pub fn shared_side() -> bool

2026-09-25: METRALE_DS41_SHARED_SIDE, read once (default on; 0 turns it off): at one token the shared expert runs on a side stream while the main stream runs the router and the host picks the experts. Its output is added into acc after the routed experts, the same point as on the main stream, so the accumulation order does not change.