Run two scan engines in parallel.
Why this one
Two engines weren't just about more coverage. They gave more data points for knowing what actually needs fixing. When both engines flag the same violation in different language, the user gets a triangulated read on the issue. When only one catches something, the dashboard shows which engine found it, which turns into its own learning surface, so builders end up understanding their codebase better than they would with a black-box tool. For a free product whose whole value prop is "trust this more than the lazy alternative," giving people more diagnostic information was worth it.
The trade-off
It cost real time. Adding the second engine extended the build by weeks rather than days, and the deduplication logic was non-trivial on its own: the same violation would come back from both engines with different wording, severity, and DOM paths. I'd still do it, because the value prop falls apart without it.