Answer stability round 1: 0 🔴, 2 🟡; seed the withheld-mark carries once per line, pin the single highlight around a link

src/markdown/emit/inline-line.ts

@@ -54,7 +54,7 @@ export function openingLinkTakesDirective(nodes: readonly AdfNode[], path: Conve
 }
 
 export function portableLineFallback(nodes: readonly AdfNode[], container: LineContainer, path: ConvertErrorPath): Result<PortableLineFallback | undefined> {
-  const emission = lineSegments(nodes, container, path, { carried: new Set(), flavour: 'portable', openingLinkAsDirective: false })
+  const emission = lineSegments(nodes, container, path, freshFallbacks(nodes, 'portable'))
   if (!emission.ok) return emission
   if (emission.value.carry !== undefined) return failure('unsupported-node-shape', 'an inline node on a portable line has no spelling but the carry', path)
   const verdict = lineVerdict(emission.value.segments, container, 'portable')
@@ -80,7 +80,7 @@ export function tryImageLine(alt: string | undefined, url: string, link?: LinkDe
 }
 
 function emitLine(nodes: readonly AdfNode[], container: LineContainer, path: ConvertErrorPath, flavour: WrittenFlavour): Result<EmittedLine> {
-  const fallbacks: LineFallbacks = { carried: new Set(), flavour, openingLinkAsDirective: false }
+  const fallbacks = freshFallbacks(nodes, flavour)
   // Terminates because takeFallback refuses a pass that took no new fallback.
   for (;;) {
     const emission = lineSegments(nodes, container, path, fallbacks)
@@ -99,6 +99,16 @@ function emitLine(nodes: readonly AdfNode[], container: LineContainer, path: Con
   }
 }
 
+// Seeds the withheld-mark carries once per line, so no run at any depth reads a node's marks whole.
+function freshFallbacks(nodes: readonly AdfNode[], flavour: WrittenFlavour): LineFallbacks {
+  const carried = new Set<number>()
+  for (const [index, node] of nodes.entries()) {
+    const taken = takenMarkTypes(node)
+    if (taken !== undefined && nodeMarks(node).some((mark) => !taken.includes(mark.type))) carried.add(index)
+  }
+  return { carried, flavour, openingLinkAsDirective: false }
+}
+
 function takeFallback(fallbacks: LineFallbacks, fallback: NodeRange | 'opening-link', path: ConvertErrorPath): Result<null> {
   if (fallback === 'opening-link') {
     if (fallbacks.openingLinkAsDirective) return failure('unsupported-node-shape', 'an opening link spelled as a directive still reads as a link definition, so the line has no spelling left', path)
@@ -221,10 +231,9 @@ function nodePath(context: InlineContext, index: number): ConvertErrorPath {
   return [...context.path, 'content', index]
 }
 
-// Decides the text-node, withheld-mark and slot-fault carries up front, so a line holding many of them is emitted once.
+// Decides the text-node and slot-fault carries up front, so a line holding many of them is emitted once.
 function carries(node: AdfNode, carried: ReadonlySet<number>, index: number): boolean {
-  const taken = takenMarkTypes(node)
-  if (carried.has(index) || (taken !== undefined && nodeMarks(node).some((mark) => !taken.includes(mark.type)))) return true
+  if (carried.has(index)) return true
   if (node.type === 'text') return !isSpellableText(node) || typeof node.text !== 'string' || node.text === ''
   const model = inlineNodeModel(node.type)
   if (model === undefined) return true

src/markdown/parse/portable-markdown-to-adf.test.ts

@@ -219,6 +219,7 @@ test('reads a == pair to the editor default highlight, Yellow200 #f8e6a0 in @atl
   assert.deepEqual(read('**==hi==** b\n'), [paragraph(text('hi', highlight, strong), text(' b'))])
   assert.deepEqual(read('==**a**_b_ `c`==\n'), [paragraph(text('a', highlight, strong), text('b', highlight, em), text(' ', highlight), text('c', code))])
   assert.deepEqual(read('==`a`==\n'), [paragraph(text('a', code))])
+  assert.deepEqual(read('==[==a==](/u) b==\n'), [paragraph(text('a', { attrs: { href: '/u' }, type: 'link' }, highlight), text(' b', highlight))])
   assert.deepEqual(read('x==y==z ==a == b==, (==c==) _d_==e==\n'), [paragraph(text('x==y==z '), text('a == b', highlight), text(', ('), text('c', highlight), text(') '), text('d', em), text('e', highlight))])
   assert.deepEqual(read('😀==b== ==c==😀 é==d==\n'), [paragraph(text('😀'), text('b', highlight), text(' '), text('c', highlight), text('😀 é==d=='))])
   assert.deepEqual(read('この機能は==日本語==でのみ、中文==重点==内容、ภาษา==ไทย==ดี 𠀀==𠀁==𠀂 이 기능은 ==한국어==에서만 サーバー==停止==中 このiPhone==専用==アプリ\n'), [