Northwind Commerce (name changed) hired a renowned visual studio. Traffic cratered. This is the engineering post-mortem, not the dribbble thread.
What changed
We moved category filters to the client, introduced a JS-only facet router, and compressed hero media aggressively — but served LCP assets too late on 4G.
Failure modes
- Hundreds of legacy URLs 404’d because redirect maps lived in a spreadsheet nobody imported.
- Faceted URLs stopped being crawlable — infinite combinations bloomed without canonical discipline.
- INP regressed because third-party personalization blocked the main thread.
Recovery playbook
- Pre-launch crawl diff with archived sitemaps.
- Server-render first paint for top templates; hydrate after.
- Alerting on organic sessions with week-over-week guardrails.
Good design and good SEO are compatible — but only if performance and routing are acceptance criteria, not tickets filed later.
