8ff57ddb452aaa28d0d425aea6dc22b5ee3fb2e3  ASSERTION FAILED: layer.renderer().isStickilyPositioned() with -webkit-box-reflect on a position:sticky element

Classified as not security-relevant.
Triage note: requiresCompositingForPosition() for sticky layers now queries renderer.layer() (with a null check) instead of the passed `layer`, which under rendererForCompositingTests() could be a RenderReplica's layer. Rendering/compositing correctness for reflected sticky content; no clear security impact.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+3.0), null_guard (+1.2), msg_soft (+1.0), area:Source/WebCore/rendering (+2.0), surgical (+1.3)