Answer the architecture pass: the empty {attrs}, the reserved fence and where the reader lives

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

@@ -1,6 +1,7 @@
 import type { AdfDocument, AdfNode } from '../../adf/document.ts'
 import type { Block, DirectiveBlock } from './blocks.ts'
 import type { LinkDefinitions } from './inline-content.ts'
+import { carryName } from '../opaque-carry.ts'
 import { failure, faulted, success, type ConvertErrorPath, type Result } from '../../result.ts'
 import { largestNesting } from '../../nesting.ts'
 import { parseBlocks } from './blocks.ts'
@@ -32,7 +33,7 @@ function blockNode(block: Block, definitions: LinkDefinitions, path: ConvertErro
     case 'bulletList':
       return listNode({ type: 'bulletList' }, block.items, definitions, path, depth)
     case 'code':
-      return success(codeBlockNode(block.language, block.text))
+      return codeBlockNode(block.language, block.text, path)
     case 'directive':
       return directiveNode(block, definitions, path, depth)
     case 'fault':
@@ -92,9 +93,10 @@ function listNode(node: AdfNode, items: readonly Block[][], definitions: LinkDef
   return success({ ...node, content })
 }
 
-function codeBlockNode(language: string, text: string): AdfNode {
+function codeBlockNode(language: string, text: string, path: ConvertErrorPath): Result<AdfNode> {
+  if (language === carryName) return failure('malformed-directive', `the info string ${carryName} is reserved for the opaque carry`, path)
   const node: AdfNode = language === '' ? { type: 'codeBlock' } : { attrs: { language }, type: 'codeBlock' }
-  return text === '' ? node : { ...node, content: [{ text, type: 'text' }] }
+  return success(text === '' ? node : { ...node, content: [{ text, type: 'text' }] })
 }
 
 // spec/flavour.md, The CommonMark image: only a plain paragraph gives an image the block it needs.