Perfformance: Lazy-load editor images

[priethor]

What

Add loading="lazy" and decoding="async" to three <img> tags in the editor shell:

• The cover image in the document-cover block
• The image variant of PageIcon (sidebar and command palette)
• The featured-image preview in PageInspectorSidebar

Why

None of these are on screen at first render, so the browser doesn't need to fetch or decode them eagerly. decoding="async" also lets the decode work happen off the main thread.

WordPress core sets the same attributes on the public frontend via wp_get_attachment_image(). This brings the editor's own <img> tags in line.

Test plan

• Open a document with a cover and a featured image; reload with the Network tab open.
• Off-screen images should load only after scrolling them into view.
• No visible layout shift.

[github-actions]

Performance vs main

Workload changed in 2 scenarios. 6 scenarios with notable timing changes.

Scenario	Workload	Timing
Open rows page 50	-	p50 -22.6%
Load rows with heavy rollups	-	p50 -17.2%
Open a row detail (resolve and hydrate)	-	Resolve p50 +20.4%
Paginate to rollups	-	rows API -20.4%
Open page in editor	+1 REST request	-
Open command palette	-	ready -17.6%
Open workspace home	+1 REST request	-
Navigate to next row	-	long tasks -34.3%

Full numbers in the job summary.