0 0 3 JavaScript

Don't outline Suspense boundaries with suspensey CSS during shell flush (#35824)

When flushing the shell, stylesheets with precedence are emitted in the
`<head>` which blocks paint regardless. Outlining a boundary solely
because it has suspensey CSS provides no benefit during the shell flush
and causes a higher-level fallback to be shown unnecessarily (e.g.
"Middle Fallback" instead of "Inner Fallback").

This change passes a flushingInShell flag to hasSuspenseyContent so the
host config can skip stylesheet-only suspensey content when flushing the
shell. Suspensey images (used for ViewTransition animation reveals)
still trigger outlining during the shell since their motivation is
different.

When flushing streamed completions the behavior is unchanged — suspensey
CSS still causes outlining so the parent content can display sooner
while the stylesheet loads.

Josh Story committed 6mo ago

38cd020c1fb8a1e88b7852160796f411926a6fac

Parent: f247eba

Committed by GitHub <noreply@github.com> on 2/19/2026, 8:29:21 PM