fix(docx-io): keep every nested inline formatting tag on DOCX export

[vincent69001]

• Auto release

🐛 Fixes ➖ N/A
🧭 Task plan: docs/plans/2026-10-07-fix-docx-io-nested-inline-formatting.md
🟢 95% confidence in the verified package behavior

Phase	🧪 Tests	🌐 Browser
Reproduced	🔴 On main, 5 of the new htmlToDocxBlob rows and the new round-trip case fail: <em><b>bold italic</b></em> exports <w:b/> only	➖ N/A
Verified	🟢 15-row matrix plus highlight test (49 pass), app round trip (6 pass), docx-io build/typecheck/brl, pnpm check	➖ N/A: no browser surface

✅ Outcome

htmlToDocxBlob, and therefore exportToDocx and DocxExportPlugin, apply every enclosing inline formatting tag to a text run. A leaf that carries several marks keeps all of them in the DOCX, and a mark no longer leaks onto the sibling text that follows a nested tag.

Plate's static renderer emits one tag per mark plugin, nested, for a multi-mark leaf. With BoldPlugin and ItalicPlugin, { text: 'bold italic', bold: true, italic: true } becomes:

<span data-slate-leaf="true" ...><em class="slate-italic"><strong class="slate-bold"><span data-slate-string="true">bold italic</span></strong></em></span>

HTML	<w:rPr> on main	<w:rPr> with this PR
<p><em><b>bold italic</b></em></p>	<w:b/>	<w:b/> <w:i/>
<p><b><em>bold italic</em></b></p>	<w:i/>	<w:b/> <w:i/>
<p><u><em><b>all three</b></em></u></p>	<w:b/>	<w:b/> <w:i/> <w:u/>
<p><span><u><em><b>x</b></em></u></span></p>	<w:b/>	<w:b/> <w:i/> <w:u/>
<p><b><em>p <s>q</s></em><u>r</u></b></p>	r: <w:b/> <w:i/> <w:u/>	r: <w:b/> <w:u/>
<p><mark>a <code>x</code> c</mark></p>	x: two <w:highlight>	x: <w:highlight w:val="lightGray"/>
<p><b>a <em>b</em></b></p>	a: <w:b/>; b: <w:b/> <w:i/>	unchanged
<p><b><em>x</em> tail</b></p>	x: <w:b/> <w:i/>; tail: <w:b/>	unchanged
<p><em>a <b>x</b> c</em></p>	a: <w:i/>; x: <w:i/> <w:b/>; c: <w:i/>	unchanged
<p><em>a</em><b>b</b></p>	a: <w:i/>; b: <w:b/>	unchanged
<p><em><span><b>bold italic</b></span></em></p>	<w:i/> <w:b/>	unchanged

Cause: in buildRun (packages/docx-io/src/lib/internal/helpers/xml-builder.ts), the formatting-tag loop flattened the subtree into one queue and reset tempAttributes = {} at every formatting tag. The flag was only folded into the durable attributes when the tag had more than one child, so a single-child chain kept the innermost flag only, and a multi-child chain leaked its flags to the siblings that followed (r above).

⚠️ Caveat

Child order inside <w:rPr> still follows attribute insertion order, as before. Inside a formatting tag, <br> is still dropped and <a> still loses its hyperlink; both are pre-existing and out of scope. When highlight tags (mark, code, kbd) or vertical-alignment tags (sub, sup) nest, the innermost one wins, which keeps one <w:highlight> / <w:vertAlign> per run. Hosted CI fails on pnpm test:slowest for packages/markdown/src/lib/table.spec.ts and apps/www/src/registry/ui/media-file-node.spec.tsx, neither touched here; the same gate failed on #5145 and #5148 before they merged.

🏗️ Design

Each queued node now carries the run attributes inherited from its formatting ancestors, the way the span branch already passes { ...attributes, ...tempAttributes } down. The children.length > 1 heuristic and the reset go away. The loop is kept rather than recursing through buildRunOrRuns, because buildRun does not descend into tags such as <a> or <abbr> and the loop keeps their text today. buildFormatting and the runPropertiesFragment import stay, because they still feed the run emitted for an empty tag. The change is confined to this branch of buildRun; no public API or export changes.

🧪 Verified

• Reproduced on main with the new tests: 5 of the first 10 matrix rows and the app round-trip case fail.
• bun test ./packages/docx-io/src/lib/internal/html-to-docx.slow.ts: 49 pass.
• bun test ./apps/www/src/__tests__/package-integration/docx-io.roundtrip.slow.tsx: a bold italic leaf round trips through serializeHtml → htmlToDocxBlob → mammoth import (fails on main with italic missing).
• pnpm turbo build --filter=./packages/docx-io, pnpm turbo typecheck --filter=./packages/docx-io, pnpm turbo brl --filter=./packages/docx-io (no barrel drift), pnpm lint:fix, pnpm check: pass.
• pnpm check was rerun after rebasing on main at 53.3.11.

AI-assisted (Claude Code), fully tested. Codex is not installed on the contributor's machine, so codex review --base origin/main was not run; the repo autoreview helper could not authenticate its nested Claude CLI, so an independent Claude review pass was run on the diff instead and its findings (nested highlight duplication, matrix coverage, changeset wording) are addressed.

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🦋 Changeset detected

Latest commit: 2c9dfda

The changes in this PR will be included in the next version bump.

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