Create plenty-wasps-sleep.md

Author: floriskn

.changeset/plenty-wasps-sleep.md

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+---
+'svelte': patch
+---
+
+fix: ensure undefined attributes are removed during hydration
+
+Attributes set server-side but undefined on the client should be removed during hydration.
+This ensures expected cleanup behavior and resolves a mismatch between SSR and client-side rendering.
+
+Fixes sveltejs/kit#13890