[chubes4]

Fixes #2156

Root cause

preserveDomStrategy.emitChild (packages/blocks-engine/src/theme/preserve-dom/strategy.ts) lowers a text-only <div>/<span> to core/paragraph, carrying the source classes onto the emitted <p>. A div has no block margins of its own, but the rendered <p> inherits the user-agent margin-block: 1em wherever the author CSS is silent on that side. The carried source CSS (e.g. Tailwind utilities) sets only what the source authored — Tailwind's preflight reset is not part of the projected styles — so the lowered box rendered taller than the source (footer copyright: margin-bottom: 14px from UA, footer 451px vs 437px).

Fix

• Paragraphs synthesized from non-paragraph source text (text-only div/span, stray inline text) are marker-classed with an engine-owned is-lowered-text class.

• The strategy drains a zero-specificity support rule through the existing dedup CSS channel (only when lowered paragraphs exist):

  :where(p.is-lowered-text){margin-block-start:0;margin-block-end:0}

  Zero specificity is the load-bearing property: as author-origin CSS it beats UA defaults, while losing to every authored rule (class, tag, or inline) by specificity — so authored margins like mt-12/mb-4 still win the cascade, and the source box's margins (0 unless authored) are preserved.

• Real <p> sources are untouched — their UA margins are part of the source.

Render-level evidence

Same section, same minimal block theme (carried utilities + engine support rule only, blockGap: null so no theme styles mask the UA defaults), measured computed values in Chromium via Playwright against a disposable WordPress:

element	before (trunk markup)	after (fixed markup)
lowered <p class="mt-12 pt-6 border-t text-center text-sm"> margin-bottom	14px (UA 1em)	0px
same, margin-top (authored .mt-12 preserved)	48px	48px
real <p class="real-copy text-sm"> margin-bottom (UA kept)	14px	14px (unchanged)

Live-import reference (unfixed import) showed the same symptom: lowered copyright <p> computed margin-bottom: 14px, margin-top: 48px, footer height 451px.

Tests

• New regression tests in src/theme/preserve-dom/__tests__/strategy.test.ts: a text-only div lowers with source classes + marker and the support rule drains; a real <p> in the same section is untouched; stray inline text is marker-classed too.
• Updated two existing expectations whose span-derived paragraphs now carry the marker.
• pnpm typecheck passes. Package suite: 497 passed; the only failures are pre-existing on unchanged origin/trunk (verified in a detached scratch worktree): wp-runtime-bundle.test.ts requires a prior pnpm build, and file-save-validity.test.ts fails a role="none" RichText assertion unrelated to this change.

AI assistance: GLM-5.3 Flash via OpenCode implemented the fix and tests; Claude (Anthropic) via OpenCode localized the issue and orchestrated. Directed by @chubes4.

[chubes4]

The original commit here fixed the TypeScript preserve-dom strategy. The real import runs through the PHP transformer, where the footer copyright still rendered margin-bottom:14px (verified in a full-site import built with this branch). Commit 0431921 adds the PHP fix:

• HtmlCompilation::paragraphBlockFromInlineContentWrapper() is the path that lowers a margin-styled text-only div to core/paragraph. It now marks that paragraph blocks-engine-lowered-paragraph.
• EngineSupportCss emits :root :where(p.blocks-engine-lowered-paragraph){margin-block-start:0;margin-block-end:0} before author CSS, only when a marked paragraph exists, so authored margins still win.
• Real <p>, blockquote, and synthetic inline wrappers (which already carry their own reset) are not marked.
• New tests/unit/lowered-paragraph-margin.php (5 assertions) fails without the fix. One existing expectation in list-item-lowering.php was updated for the new class.
• composer test:unit and composer test both pass.

AI assistance: Claude (Anthropic) via OpenCode found the gap in the live import and wrote the PHP fix and test. Directed by @chubes4.