Lower structural lists into editable native groups

[chubes4]

Summary

• keep block-level list-item subtrees out of core/list-item RichText attributes
• lower structural ul/ol collections and their li items into semantic core/group blocks with editable native children
• retain representable text, inline formatting, links, and direct nested lists as native core/list blocks
• preserve author selector behavior through generic source-tag and semantic carrier projection
• measure structural HTML stored in known RichText attributes by count and bytes

Architecture

The decision uses DOM element categories and WordPress block grammar only. It has no source-format, fixture-path, generated-node, or authored-class branching.

A structural list keeps its source ul or ol wrapper through core/group.tagName; each structural item keeps li through the same native Group contract. Item descendants recursively use existing heading, paragraph, image, list, control, and layout conversions. CSS-addressed inline leaves receive independent native carriers where RichText normalization would alter layout.

Evidence

• composer test passes
• 278 PHP transformer parity fixtures pass
• package-install proof passes
• WordPress site-plan integration passes
• generic Chromium visual parity passes
• real-design fixture compilation records zero structural RichText violations and zero structural RichText bytes across every generated page
• worktree is clean at 3a908512

The solved-site promotion gate is still pending before fixture execution because its pinned WP Codebox installation is stalled. Responsive layout, forms, and unrelated HTML-bearing constructs remain separate work.

Closes #894.

AI assistance

OpenAI GPT-5.6 Sol through OpenCode audited the generated artifact, traced the generic lowering and selector-projection paths, implemented the repair and tests, and ran the deterministic and real-fixture verification. Chris Huber reviewed the evidence and remains responsible for every line.