When Is RTL Better? Auditing Evaluation Stability with Tool-Grounded Requirement Profiles
RTL-generation studies increasingly report functional correctness and post-synthesis quality, yet the evaluator itself is rarely treated as an experimental variable. A candidate can appear better when a security rule, protocol obligation, target context, feasibility gate, uncertainty policy, or provenance constraint is omitted. We introduce tool-grounded requirement profiles: machine-readable contracts binding each requirement's meaning to its executable evidence and comparison rule, together with cross-requirement gates, uncertainty handling, and provenance. We audit evaluator stability by freezing candidate pairs and perturbing only their evaluation profile. In a preregistered controlled pilot with six designs, twelve pairs, three requirement families, six evaluator conditions, and 72 decisions, a generic cell-count evaluator reports unsupported improvement for 6/12 pairs (50%; Wilson 95% interval 25.4 to 74.6%; design-cluster bootstrap interval 25 to 75%). The matched evaluator detects all twelve injected regressions, whereas syntax, generic synthesis, context mismatch, and gate ablation each lose the required distinction for 12/12 pairs. In a separately frozen external validation of all 290 public RTLLM v1.1 text-only candidates, 81/215 evaluable comparisons (37.7%; task-cluster 95% interval 24.8 to 51.4%) yield unsupported scalar improvements, including 72 functional-gate reversals. Separately, 26 OpenROAD-flow-scripts runs show why timing context and activity qualification must be part of the contract. The study does not rank generators; it establishes evaluator configuration as a measurable, auditable source of conclusion instability.