Every performance decision here was made from a Lighthouse run somebody did by
hand in DevTools and typed into a conversation. That loop is slow and it is
lossy: nothing measured after a build, so three real defects sat live for weeks
— a `sizes` that overstated a column by 48px, font preloads that had gone
missing, an LCP image left lazy by a rename.
api/lighthouse.ts runs it: both form factors in about 20 seconds, four
categories, the five metrics, and every failing audit with the resources it
names. A finding that says "Improve image delivery — 32 KiB" is not actionable;
the same finding with the URL and the size served is a one-line fix.
The browser is looked for in three places before anything is downloaded —
CHROME_PATH, chrome-launcher's own search, then the Chrome-family binaries by
name, which is what finds the Brave already on this machine. chrome-launcher
THROWS rather than returning null when it finds nothing, so an unguarded call
never reaches the fallback; that is caught. Only if all three miss does
@puppeteer/browsers fetch one, as a library call rather than a postinstall,
because bun does not run postinstall for an untrusted package and a silent no-op
there would surface as a failure at the first audit.
First result: Total Blocking Time is 0 ms on both form factors, down from 130.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
