Answer stability round 3: a link directive holding a joined hard break falls back to parting it

src/markdown/emit/adf-to-markdown.test.ts

@@ -722,6 +722,9 @@ test('spells a mark run across the hard break between two nodes holding the mark
   assert.equal(readsBack(document(paragraph(marked('a', link), hardBreak, marked('b', link)))), '[a\\\nb](/u)\n')
   assert.equal(readsBack(document(paragraph(marked('a', em, link), hardBreak, marked('b', em)))), '_[a](/u)\\\nb_\n')
   assert.equal(readsBack(document(paragraph(marked('a', em), hardBreak, hardBreak, marked('b', em)))), '_a\\\n\\\nb_\n')
+  const directive: AdfMark = { attrs: { href: '/u', id: 'x' }, type: 'link' }
+  assert.equal(readsBack(document(paragraph(marked('a', directive), hardBreak, marked('b', directive)))), '!adf:link[a]{href="/u" id=x}\\\n!adf:link[b]{href="/u" id=x}\n')
+  readsBack(document(paragraph(marked(']: /x', link, { type: 'code' }), hardBreak, marked('b', link))))
   assert.equal(readsBack(document(paragraph({ text: 'x', type: 'text' }, marked('.', em), hardBreak, marked('b', em)))), 'x!adf:carry{json="{\\"marks\\":[{\\"type\\":\\"em\\"}],\\"text\\":\\".\\",\\"type\\":\\"text\\"}"}\\\n_b_\n')
 })
 

src/markdown/emit/inline-line.ts

@@ -327,6 +327,8 @@ function emitMarkedRun(nodes: readonly AdfNode[], mark: AdfMark, depth: number,
   const inner = emitRun(nodes, depth + 1, index, { ...context, bracketed: true })
   if (!inner.ok) return inner
   if (inner.value.carry !== undefined) return inner
+  // A link `tryLink` gave back holds the hard breaks `joinsRun` joined; the carry's fallback parts them.
+  if (inner.value.segments.some((segment) => segment.text.includes('\n'))) return success({ carry: range })
   return success({ segments: [syntax(spellInlineDirectiveOpener(mark.type)), ...inner.value.segments, syntax(`]${attributes}`)] })
 }
 

todo.md

@@ -325,8 +325,8 @@ quadratic in a run of blanks inside one leaf: a paragraph of `a`, 80 000 spaces,
 `adfToLosslessMarkdown` spends 23 s on one paragraph of 2000 × `un` plus `**-r**`: each run its
 flanking cannot spell re-emits the whole line before riding the carry, quadratic in the runs, and
 the portable reduction's `spellableLine` drops one mark per re-emit the same way. An inline node
-whose attributes no spelling writes re-emits the line the same way before riding the carry. Make all
-three linear.
+whose attributes no spelling writes re-emits the line the same way before riding the carry, and so
+does an emphasis or link run that parts at the hard breaks it spans. Make all four linear.
 
 ### 56. Give each piece of `blocks.ts`'s block-walk state and `inline-content.ts`'s `Scan` one owner that returns what it changes.