bscost-theory-optlisted

# BS Cost Theory Opt Use this skill when the task is to move from heuristic cost terms to a validated optimization model that can be promoted only after passing gates. ## Step 1: Lock metric contract before fitting 1. Use signed target: - `delta_tau_ps = tau_back_ps - tau_front_ps` 2. Use signed model output: - `delta_cost = cost_back - cost_front` 3. Keep compatibility fields: - `cost_front`, `cost_back`, `min_cost` 4. Gate-0 contract checks are mandatory before any optimization claim. ## Step 2: Theory-grounded feature setup Build from physically meaningful inputs first: 1. Geometry: - pin-based HPWL and bbox features 2. Front/back timing proxy: - PDK timing proxy, via proxy, fanout/load terms 3. Backside overhead: - nTSV/stack-via related terms (or best available proxy) Use shared feature names across signal and clock tracks where possible. Load: - `references/theory_formulation.md` ## Step 3: Optimization procedure 1. Compare against HPWL baseline with identical split strategy. 2. Use repeated cross-validation (default 5x2). 3. Report per-fold and per-dataset metrics: - Pearson - Spearman - sign accuracy 4. Use same train/test partitions for baseline and candidate model. Load: - `references/optimization_and_gates.md` ## Step 4: Promotion gates (stable > HPWL) Model can be promoted only if: 1. Gate-0 pass: - contract valid - sign convention fixed 2. Gate-1 (delay consistency) pass on all target datasets: - `delta_pearson > 0`