2026-07-04 — v18 first impression pass

July 4, 2026

The viewer now opens on a real rendered trace instead of a blank canvas: the bundled sample auto-loads on first visit, the chromatogram background follows the active theme, and the UI explicitly tells you that you are looking at a sample until you dismiss or replace it.

What shipped

First visit auto-loads public/sample.ab1 through the normal parse/render path.
User-loaded files replace the placeholder sample slot instead of silently creating a second tab.
A dismissible sample ribbon explains that the app is 100% in-browser and ready for your own trace.
The chromatogram canvas now paints with --color-surface instead of a hardcoded white fill.

Verification added

tests/parsers/sample.test.ts locks the bundled sample to exact known base-call values.
tests/e2e/ux-a11y.e2e.test.ts covers first-visit sample rendering, sample ribbon behavior, single-slot replacement, and dark-surface loading.