GFM extension fallbacks must preserve user-visible syntax

Problem

Two GFM seams were lying in different ways:

• autolink literals parsed as links, but serialized back as [url](url)
• footnote references and definitions were not modeled, so the fallback dropped the [^id] marker entirely

Both failures broke the same rule: if Plate cannot preserve the exact feature model yet, it still has to preserve the syntax users actually typed.

Root Cause

• The markdown link serializer always emitted a normal link node, which let remark-stringify choose bracket-link output.
• The footnote fallback only flattened definition children into paragraphs and left footnoteReference without a deserializer, so the marker vanished.

Solution

Autolink literal

When a link node is just a plain URL with identical text and href, serialize it as raw markdown text instead of a normal link node, unless the caller explicitly forces resource links:

const isBareAutolinkLiteral =
  children.length === 1 &&
  children[0]?.type === 'text' &&
  children[0].value === node.url &&
  options.remarkStringifyOptions?.resourceLink !== true &&
  BARE_AUTOLINK_PROTOCOL_REGEX.test(node.url ?? '');

if (isBareAutolinkLiteral) {
  return {
    type: 'html',
    value: node.url,
  };
}

That preserves:

https://platejs.org

instead of degrading to:

[https://platejs.org](https://platejs.org)

But when the caller sets remarkStringifyOptions.resourceLink = true, return the normal mdast link node and let remark-stringify emit:

[https://platejs.org](https://platejs.org)

Footnote fallback

Until Plate has a first-class footnote model:

• deserialize [^id] references into literal text nodes
• deserialize definitions into plain paragraphs with the label on the first block

That keeps the visible syntax alive:

[^1]

[^1]: Footnote text

instead of silently dropping the reference marker.

Why This Works

There are two levels of correctness:

1. full semantic support
2. syntax-preserving fallback

If full support is not there yet, fallback still needs to preserve what the user sees and typed. Losing the marker or rewriting a URL into a different link form is data drift, not a harmless implementation detail.

Serializer fallbacks also have to stay below caller-controlled stringify options. If an option like resourceLink exists specifically to force a markdown wire shape, the Plate shortcut should yield the normal mdast node and let remark-stringify honor that setting.

Prevention

• For every unsupported or partially supported markdown extension, define an explicit fallback contract.
• Fallback contracts should preserve user-visible syntax before they preserve internal shape convenience.
• Before returning raw markdown/html from a serializer shortcut, check whether remarkStringifyOptions already exposes the caller's requested wire shape.
• Add package-surface tests for:
  • parse
  • serialize
  • deserialize after serialize
  • explicit remarkStringifyOptions overrides for the same surface
• Do not accept "the text is still there somewhere" as good enough when the syntax itself carries meaning.

Verification

These checks passed:

bun test packages/markdown/src/lib/gfmSurface.spec.ts packages/markdown/src/lib/commonmarkSurface.spec.ts packages/markdown/src/lib/defaultRules.spec.ts apps/www/src/__tests__/package-integration/markdown-rich/defaultRule.spec.ts packages/link/src/lib/withLink.spec.tsx
pnpm lint:fix

Additional resource-link regression:

pnpm exec bun test packages/markdown/src/lib/gfmSurface.spec.ts
pnpm turbo build --filter=./packages/markdown
pnpm build
pnpm turbo typecheck --filter=./packages/markdown
pnpm lint:fix