Constant HORNER_SEQ_BUDGET 

pub const HORNER_SEQ_BUDGET: f64 = 5.0;

The stage budget fabric_horner_seq is cut to, in the units of op_delay. MEASURED (2026-10-17, the synthesis sequence of OpenLane’s synth.tcl under host yosys 0.33, AREA 0, abc target 1 ns, sky130_fd_sc_hd tt_025C_1v80, worst stage by abc stime): budget 4 is 1.36 ns over 311,772 µm² of cells, 5 is 1.43 ns over 258,289 µm², 6 is 1.99 ns, 7 is 2.65 ns; the single-stage residual is 13.85 ns. Five is the knee: the next tighter budget buys 5% of period for 21% more area.