LCP discovery deterministic trace pack

#419817756 P3 Status: New DevTools trace insights / Lighthouse parity

Scope

Trace-only sampler

Live HTML reproductions were not deterministic enough across Chromium builds.

This sampler now keeps only deterministic trace files for A/B comparison in devtools-demo.

Downloads

Use the same trace in unpatched and patched builds

Trace: lazy + preload auto Trace: lazy + preload high Zip: both traces

How to validate in devtools-demo 3

  1. Open DevTools Performance panel.
  2. Load one trace using "Load profile" (or drag and drop).
  3. Open Insights and compare unpatched vs patched output.

Expected results (verification matrix)

Important: for trace-lazy-preload-high on patched builds, check 📂 Passed insights.

Trace Where to find card Unpatched expected Patched expected
trace-lazy-preload-auto Non-passing insights (both builds) 🔴 fetchpriority=high should be applied
🟢 Request is discoverable in initial document
🔴 lazy load not applied
🔴 fetchpriority=high should be applied to the image preload request
🟢 Request is discoverable in initial document
🔴 lazy load not applied
trace-lazy-preload-high Unpatched: non-passing. Patched: usually in 📂 Passed insights. 🟢 fetchpriority=high applied
🟢 Request is discoverable in initial document
🔴 lazy checklist row
🟢 fetchpriority=high applied
🟢 Request is discoverable in initial document
🟢 lazy checklist row (mitigated by high-priority preload)
🟢 Insight overall is passing

References

Chromium issue 419817756

Lighthouse issue 16034

Lighthouse discussion context