Capture WordPress REST preload waterfalls

[chubes4]

Summary

• Add browser-side WordPress REST instrumentation that records wp.apiFetch and fetch attempts during page profiling.
• Correlate client REST attempts with observed network requests to classify network hits, inferred preload/cache hits, and remaining preload opportunities.
• Add baseline-vs-candidate REST waterfall comparison helpers plus markdown report output for PR evidence.

Verification

• node wordpress/tests/page-profiler-smoke.js
• node --check wordpress/lib/page-profiler.js
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (openai/gpt-5.5)
• Used for: Audited the Homeboy extension/rig boundaries, drafted the WordPress REST waterfall instrumentation and smoke coverage, and ran targeted validation. Chris remains responsible for review and testing.

Related

• Enables REST waterfall evidence for Editor: Preload initial Site Editor canvas data WordPress/wordpress-develop#11766 and similar wp-admin performance work.
• Gutenberg companion: Site Editor: preload initial canvas data WordPress/gutenberg#78075