Function moe_grouped_decode_forced 

pub fn moe_grouped_decode_forced() -> bool

Force the grouped arm BELOW moe_grouped_decode_min_rows(). Diagnostic only — it exists so the n=5..15 gap can be measured without a rebuild, and it is the same var #415’s measurements used, kept working on purpose. Never a production setting: if forcing wins at a width, move the THRESHOLD.