Propagate CSS namespace context into functional pseudo-class selector lists #520

Problem

Namespace context must propagate into selectors nested inside functional pseudo-classes such as :is(), :where(), :not(), and reachable :has() arguments. The initial namespace slice covers top-level compiled type/universal compounds only.

Scope

• Preserve the enclosing stylesheet namespace map while recursively compiling functional selector lists.
• Include namespace context in nested selector payload/cache identity and invalidation dependencies.
• Cover mixed prefixed/default/any/empty namespace arguments, unknown prefixes, nesting, dynamic CSSOM mutation, adopted sheets, and :has() relative matching.
• Add browser-referenced WPT/native contracts plus bounded invalidation, performance, and lifecycle gates.

Parent: #239. Depends on the type/universal namespace selector slice; coordinate with #237 selector matching.

Status

Planned after the current top-level namespace implementation. No implementation or validation is claimed.