When an element was affected by :has() in subject position,
pending :has() mutation invalidation also applied the pseudo-class
invalidation plan for that element. If the same element had ever been
observed in a non-subject :has() selector, that plan could invalidate
the element's whole descendant subtree even when the mutation could
only require the subject element itself to recompute style.
Keep subject-position :has() invalidation to the element itself, and
run the descendant fanout only for non-subject involvement after the
existing mutation feature filter says that fanout may be affected.
Track the strongest invalidation applied to each anchor, so a later
batched mutation can still upgrade earlier anchor-only work to a
descendant fanout.
Extend the filter to treat known state pseudo-classes as concrete
mutation features, so a :hover mutation does not conservatively match
unrelated selectors such as :has(dialog:modal).
Scope boundary selectors are kept conservative where needed: when an
@scope boundary contains :has(), the scope root's match can activate or
deactivate style rules for descendants, so it still records descendant
involvement.
Add coverage for unrelated hover and batched mutation cases on elements
whose ancestors have both subject and non-subject :has() involvement,
ensuring descendant no-op recomputation stays bounded without dropping
required descendant fanout.
c746bd5049