WebP for the web: verify format consistency
WebP supports alpha, so a transparent PNG → WebP conversion needs no background: background.required=false and output.alpha=true.
Before publishing, verify three things: declared format, MIME type and extension. validateOutputEnvelope rejects mime="image/png" with declaredFormat="webp", and rejects an .avif filename holding PNG bytes. Correct WebP is image/webp + .webp + actual format webp.
Dragging the quality slider quickly creates a new runId per run; only the last run commits and stale results are discarded, so old parameters never overwrite new ones.
No encoder is wired this round; output is a deterministic plan JSON and real WebP encoding is untested.