Answer the second stability pass: the emitter's own refusal, and the comparator's third arm

AGENTS.md

@@ -172,7 +172,8 @@ both answer to the round-trip corpus and to nothing else where a node has no fix
   directions must answer alike — whether a list marker interrupts a paragraph — is one function
   there too, never a copy per direction, however conservative the copy would be. Where the rule is
   the emitter's own choice, input consults it rather than restating it: the parser asks
-  `spellsCommonMark` which form the emitter picks, so no fixture the emitter writes can be refused.
+  `commonMarkSpelling` which form the emitter picks, so no fixture the emitter writes can be
+  refused, and a spelling the emitter refuses gives its own error rather than a second name for it.
 - The attribute vocabulary is ADF's: `adf/` walks it and narrows each value to its kind, and a
   format spells the narrowed value. A spelling that re-checks the type is the check's second copy.
   Reading a spelling back is the format's own: the reader sits beside the spelling it inverts, so

spec/flavour.md

@@ -157,8 +157,8 @@ included, is an error result naming it. The flavour never emits raw HTML.
 The directive name is always the ADF node type. A container's body is the node's `content`; a
 leaf has none. Every directive parses in any position — `markdownToAdf` builds exactly what is
 written; validity against ADF's content models stays the author's business (AGENTS.md §14). It
-parses only in the form the emitter picks, though: a directive spelling a node CommonMark holds
+parses only in the form the emitter picks, though: a directive spelling a node the emitter would
-is a named error, the per-node plain-versus-directive choice below read backwards.
+have written as CommonMark is a named error.
 
 Each section lists attributes as `name (type)`. A parenthesized value set documents what real
 payloads hold; the type stays string and any value round-trips verbatim. Values map to attrs by

src/markdown/directive-syntax.ts

@@ -107,7 +107,8 @@ export function unknownDirectiveFault(name: string): ConvertFault {
 }
 
 function keyOrder(left: string, right: string): number {
-  return left < right ? -1 : 1
+  if (left < right) return -1
+  return left > right ? 1 : 0
 }
 
 function quote(text: string): string {

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

@@ -86,9 +86,10 @@ function emitBlock(node: AdfNode, path: ConvertErrorPath, depth: number): Result
   return emitDirectiveBlock(node, directive, path, depth)
 }
 
-// The plain-versus-directive choice is the emitter's; input reads it back rather than restating it (AGENTS.md §11).
+export function commonMarkSpelling(node: AdfNode, path: ConvertErrorPath, depth: number): Result<null> | undefined {
-export function spellsCommonMark(node: AdfNode, path: ConvertErrorPath, depth: number): boolean {
+  const readable = readableBlock(node, path, depth)
-  return readableBlock(node, path, depth) !== undefined
+  if (readable === undefined) return undefined
+  return readable.ok ? success(null) : readable
 }
 
 function readableBlock(node: AdfNode, path: ConvertErrorPath, depth: number): Result<EmittedBlock> | undefined {

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

@@ -148,7 +148,6 @@ test('reads the three directive forms into the nodes the tables name', () => {
   assert.deepEqual(content(markdownToAdf('Part:hardBreak{}.\n')), [{ content: [text('Part'), hardBreak(), text('.')], type: 'paragraph' }])
 })
 
-// The emitter's plain-versus-directive choice, read backwards: only the form it picks parses.
 test('names the directive form a node CommonMark spells refuses', () => {
   const named = (type: string): string => `unsupported-node-shape: ${type} takes the CommonMark spelling, not the directive form`
   assert.equal(content(markdownToAdf('::rule\n')), named('rule'))
@@ -160,6 +159,12 @@ test('names the directive form a node CommonMark spells refuses', () => {
   assert.deepEqual(content(markdownToAdf('::::bulletList\n:::listItem\n---\n:::\n::::\n')), [bulletList(item({ type: 'rule' }))])
 })
 
+// The spelling the emitter refuses gives the emitter's own error, never a second name for it.
+test('gives back the refusal the CommonMark spelling itself raises', () => {
+  const nested = '::::::::bulletList\n:::::::listItem\n---\n\n::::::bulletList\n:::::listItem\n---\n\n::::bulletList\n:::listItem\n---\n:::\n::::\n:::::\n::::::\n:::::::\n::::::::\n'
+  assert.equal(code(markdownToAdf(nested)), 'unspelled-block-separation')
+})
+
 test('names the directive name no node reads back to', () => {
   assert.equal(code(markdownToAdf(':::widget info\nx\n:::\n')), 'unknown-directive-name')
   assert.equal(content(markdownToAdf('::widget\n')), 'unknown-directive-name: the directive name widget reads back to no node')

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

@@ -3,12 +3,12 @@ import type { Block, DirectiveBlock } from './blocks.ts'
 import type { BlockDirectiveNode } from './directive-nodes.ts'
 import type { LinkDefinitions } from './inline-content.ts'
 import { carryName } from '../opaque-carry.ts'
+import { commonMarkSpelling } from '../emit/adf-to-markdown.ts'
 import { failure, faulted, success, type ConvertErrorPath, type Result } from '../../result.ts'
 import { largestNesting } from '../../nesting.ts'
 import { parseBlocks } from './blocks.ts'
 import { parseInlineContent } from './inline-content.ts'
 import { readBlockDirectiveNode } from './directive-nodes.ts'
-import { spellsCommonMark } from '../emit/adf-to-markdown.ts'
 
 export function markdownToAdf(markdown: string): Result<AdfDocument> {
   const parsed = parseBlocks(markdown)
@@ -58,10 +58,10 @@ function directiveNode(block: DirectiveBlock, definitions: LinkDefinitions, path
   if (!read.ok) return read
   const built = directiveBody(read.value, block.blocks, definitions, path, depth)
   if (!built.ok) return built
-  if (spellsCommonMark(built.value, path, depth)) {
+  const readable = commonMarkSpelling(built.value, path, depth)
+  if (readable === undefined) return built
+  if (!readable.ok) return readable
   return failure('unsupported-node-shape', `${built.value.type} takes the CommonMark spelling, not the directive form`, path)
-  }
-  return built
 }
 
 function directiveBody(read: BlockDirectiveNode, blocks: Block[] | undefined, definitions: LinkDefinitions, path: ConvertErrorPath, depth: number): Result<AdfNode> {

todo.md

@@ -335,6 +335,9 @@ detail is settled at its own milestone.
         `corpus.test.ts` too, and `unspelled-block-separation`, which loses its only cause here.
         The emitter's other refusals survive on causes no fixture in that directory covers, so
         3k's one-list pass is where they get fixtures or the directory goes.
+        Losing that cause closes the last shape input accepts and emit refuses — a CommonMark block
+        beside a directive one inside a list item — so the parse-then-emit fixpoint the README
+        promises holds from here rather than only for what the emitter wrote.
   - [ ] **3i — The inline nodes and the marks.** `inline-nodes/` reads back: the content slot's
         `text` attribute and the error a slot holding anything but one unmarked text node is; the
         `:text{text="…"}` whitespace spelling; the four directive marks and their nesting order,