How do you handle URL redirects?

Every legacy M1 URL gets a 301 redirect to its M2 equivalent. Three layers:

• (1) Slug-match auto-mapping — Magento’s URL rewrite migration handles 80–90% of product, category, and CMS URLs automatically (slugs unchanged).
• (2) Manual mapping — for URLs that changed (e.g. M1 .html suffix dropped, custom routes restructured), we generate a CSV of old→new and load it into M2’s url_rewrite table.
• (3) Web-server fallback — nginx / Apache rules catch anything missed at the URL-rewrite level (e.g. legacy .php paths).

Pre/post Screaming Frog crawls compare every URL — any 404s on legacy URLs get patched within 24 hours of cutover. Zero permanent 404s guarantee.