GFM literal autolinks can leave adjacent text nodes that merge on round-trip

[ChristianMurphy]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected package

mdast-util-gfm 3.1.0, mdast-util-to-markdown 2.1.2, mdast-util-from-markdown 2.0.3

Steps to reproduce

import {fromMarkdown} from 'mdast-util-from-markdown'
import {toMarkdown} from 'mdast-util-to-markdown'
import {gfm} from 'micromark-extension-gfm'
import {gfmFromMarkdown, gfmToMarkdown} from 'mdast-util-gfm'

const input = '[http://a.\n]'
const opts = {extensions: [gfm()], mdastExtensions: [gfmFromMarkdown()]}
const tree1 = fromMarkdown(input, opts)

tree₁'s paragraph has four children (note adjacent text nodes):

{
  "type": "paragraph",
  "children": [
    { "type": "text", "value": "[" },
    { "type": "link", "url": "http://a", "children": [{ "type": "text", "value": "http://a" }] },
    { "type": "text", "value": "." },
    { "type": "text", "value": "\n]" }
  ]
}

stringify and re-parse:

const text2 = toMarkdown(tree1, {extensions: [gfmToMarkdown()]})
// text2: '\\[<http://a>.\n]\n'
const tree2 = fromMarkdown(text2, opts)

tree₂'s paragraph has three children (the two trailing text nodes are
merged):

{
  "type": "paragraph",
  "children": [
    { "type": "text", "value": "[" },
    { "type": "link", "url": "http://a", "children": [{ "type": "text", "value": "http://a" }] },
    { "type": "text", "value": ".\n]" }
  ]
}

Actual behavior

Adjacent text siblings remain in tree₁ but not in tree₂, so
normalize(tree1) !== normalize(tree2) even though the rendered HTML is the
same.

Expected behavior

Either the transform that extracts the literal autolink should merge its
surrounding text splits (so tree₁ has the same three children as tree₂), or a
subsequent pass should merge adjacent text siblings.

Runtime

node v24.13.1

Package manager

No response

Operating system

Ubuntu (WSL2)

Build and bundle tools

No response