I used to treat accessibility as a final QA step. Run an axe scan, fix the contrast issues, add some aria labels, ship. It took a project with a hard WCAG 2.1 AA requirement to change how I think about it.
The insight: accessibility problems that are expensive to fix at the end are cheap to avoid at the beginning. Color contrast is easier to bake into a design system than to retrofit across 50 components. Focus order makes sense if you designed with keyboard navigation in mind from the start.
The tools I keep open during design: Figma's accessibility annotations kit, the Colour Contrast Analyser, and axe DevTools for browser-level checking. Between those three, you catch most of the big issues before a line of code is written.