Function php_instance_linear_marked_hole 

pub fn php_instance_linear_marked_hole(m: usize) -> SymmetricInstance

Linear-encoded pigeonhole with one marked hole — the hole-stabilizer instrument (Sₘ × Stab(h₀) ≅ Sₘ × Sₘ₋₂). Hole 0 gets its own sort; pigeon symmetry is untouched.