Report Site Editor REST preload waterfalls

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Summary

• Capture phase-scoped Site Editor network requests during the preload comparison workload.
• Enrich warmup and measurement profiles with the WordPress REST waterfall summary from homeboy-extensions.
• Persist REST waterfall comparison/report artifacts and headline metrics for removed, new, and remaining REST network requests.

Dependency

• Depends on Capture WordPress REST preload waterfalls Extra-Chill/homeboy-extensions#532 for the reusable WordPress REST waterfall profiler APIs.

Verification

• node --check Automattic/studio/bench/studio-site-editor-preload-comparison.bench.mjs
• node --test Automattic/studio/bench/studio-site-editor-diagnostics.test.mjs
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (openai/gpt-5.5)
• Used for: Wired the Studio preload comparison workload to the new REST waterfall profiler APIs and ran targeted syntax/unit validation. Chris remains responsible for review and benchmark evidence.

Related

• Supports evidence for Editor: Preload initial Site Editor canvas data WordPress/wordpress-develop#11766
• Gutenberg companion: Site Editor: preload initial canvas data WordPress/gutenberg#78075
• Depends on Capture WordPress REST preload waterfalls Extra-Chill/homeboy-extensions#532