Answer the stability nits: the runs a trailing-anchored regex re-walks

corpus/README.md

@@ -6,7 +6,8 @@ One directory per contract kind, each landing with its milestone:
   document, byte for byte, and that `markdownToAdf` must read back to it (AGENTS.md §2). Grouped
   by what the fixture exercises.
 - `normalization/` — `<name>.md` + `<name>.json`: markdown input, and the document
-  `markdownToAdf` must build from it. One-way; the markdown is not canonical.
+  `markdownToAdf` must build from it, which must in turn emit and read back to itself. The
+  markdown is not canonical.
 - `errors/` — `<name>.md`: markdown input that must not convert. A `<name>.error` beside it
   pins which error.
 - `real-payloads/` — `<name>.json`: sanitized live ADF, round-tripped ADF→markdown→ADF. No

src/markdown/commonmark-grammar.ts

@@ -223,6 +223,18 @@ export function setextHeadingLevel(line: string): number | undefined {
   return underline.startsWith('=') ? 1 : 2
 }
 
-export function trimSpace(text: string): string {
+function spaceOrTab(character: string): boolean {
-  return text.replace(/^[ \t]+|[ \t]+$/g, '')
+  return character === ' ' || character === '\t'
+}
+
+export function trimSpace(text: string): string {
+  let start = 0
+  while (start < text.length && spaceOrTab(text.charAt(start))) start += 1
+  return trimTrailingSpace(text.slice(start))
+}
+
+export function trimTrailingSpace(text: string): string {
+  let end = text.length
+  while (end > 0 && spaceOrTab(text.charAt(end - 1))) end -= 1
+  return text.slice(0, end)
 }

src/markdown/parse/inline-content.ts

@@ -1,7 +1,7 @@
 import type { AdfMark, AdfNode } from '../../adf/document.ts'
 import type { EmphasisPairing } from '../emphasis-matching.ts'
 import type { LinkDefinition } from '../link-syntax.ts'
-import { backslashEscape, decodeTextEscapes, inlineHtmlConstruct, readBracketedAutolink, readEmailAutolink } from '../commonmark-grammar.ts'
+import { backslashEscape, decodeTextEscapes, inlineHtmlConstruct, readBracketedAutolink, readEmailAutolink, trimTrailingSpace } from '../commonmark-grammar.ts'
 import { backtickRun, closingBacktickRun } from '../backtick-runs.ts'
 import { delimiterFlags, matchEmphasis, runLength } from '../emphasis-matching.ts'
 import { failure, faulted, success, type ConvertErrorPath, type Result } from '../../result.ts'
@@ -28,9 +28,7 @@ type Run = { canClose: boolean; canOpen: boolean; character: string; index: numb
 
 type Scan = { definitions: LinkDefinitions; path: ConvertErrorPath; pending: string; pieces: Piece[]; source: string }
 
-const hardBreakSpaces = / {2,}$/
 const imageAlone = 'an image fits only as a paragraph of its own'
-const trailingSpace = /[ \t]+$/
 
 export function parseInlineContent(source: string, definitions: LinkDefinitions, path: ConvertErrorPath): Result<InlineContent> {
   const scan: Scan = { definitions, path, pending: '', pieces: [], source }
@@ -95,7 +93,7 @@ function readBackslash(scan: Scan, index: number): number {
 }
 
 function readLineEnding(scan: Scan, index: number): number {
-  const hard = hardBreakSpaces.test(scan.pending)
+  const hard = scan.pending.endsWith('  ')
   flush(scan, true)
   if (hard) pushNode(scan, { type: 'hardBreak' })
   else scan.pending = ' '
@@ -154,7 +152,7 @@ function readDirective(scan: Scan, index: number): Result<number> {
 }
 
 function flush(scan: Scan, strip: boolean): void {
-  const raw = strip ? scan.pending.replace(trailingSpace, '') : scan.pending
+  const raw = strip ? trimTrailingSpace(scan.pending) : scan.pending
   scan.pending = ''
   if (raw !== '') scan.pieces.push({ kind: 'nodes', nodes: [{ text: decodeTextEscapes(raw), type: 'text' }] })
 }

todo-history.md

@@ -281,32 +281,7 @@ Under **3 — `markdownToAdf` (`0.1.0`)**:
         `spec/flavour.md`'s closing-fence sentence now says: a run reaching past the innermost
         leaves the fence it did not close a named error, which §2 prefers to closing more than the
         author wrote.
-  - [x] **3h — The block nodes.** `block-nodes/` reads back: the `codeBlock` directive's fenced body and the
+  - [x] **3g — The node tables read backwards.** `commonmark-subset/` reads back, the first
-      `language` attribute a bare fence leaves it; the media family's composition; and both
-      table forms, the pipe table's cell split and its named errors. `fenceInfo` is a rule both
-      directions answer alike and moves to the `markdown/` root with the language attribute.
-      **Settled** (the maintainer, 2026-08-27): 1d's last pick, the one
-      `container-block-separation` holds — a CommonMark block and a directive block sit adjacent
-      in a container body with no blank line between them. That reduces the three cases to one
-      rule, separation only where its absence would merge the blocks: the `:::` fence is
-      separation already, and 3c's claim ends the lazy continuation that would otherwise swallow
-      it. The fixture becomes a round-trip pair, and with `nested-list-separation` and 3e's pair
-      that empties `corpus/unspellable/`: this chunk settles the directory's own guard in
-      `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.
-      **Settled** (the maintainer, 2026-09-01): losing that cause closed one of the shapes input
-      accepted and emit refused, not the last. Two adjacent lists of a kind are what
-      `adfToMarkdown` refuses and one `- ` spelling cannot hold apart, and the walk reached them
-      two ways — a marker change, which CommonMark opens a second list on, and an empty last item,
-      whose blank line pops the container the list's identity hung from. The parser opens no list
-      beside one of its own kind instead, the way it already drops the blank lines between items;
-      3k owes the CommonMark suite an exception where the reference HTML holds two `<ul>`. The
-      `normalization/` arm emits each document and reads it back from here, so the population that
-      class lives in is checked rather than read. The README's canonical-fixpoint sentence still
-      claims more than the parser keeps — 3e's three shapes — which stays milestone 5's to
-      narrow.
-- [x] **3g — The node tables read backwards.** `commonmark-subset/` reads back, the first
         directory to. A parsed directive becomes its node: the name to the type and an unknown one
         to a named error, the arg to the attribute it names, each value to the type its section
         assigns, the body to `content`, the reserved `marks` key to the marks array. 3a's drift
@@ -334,3 +309,28 @@ Under **3 — `markdownToAdf` (`0.1.0`)**:
         path and returns `Result`, so no second reader took it. The drift guard earned itself on
         the way in: the spec's `text` attribute was missing from three inline table entries, which
         the content slot spells and the vocabulary walk already passes over.
+  - [x] **3h — The block nodes.** `block-nodes/` reads back: the `codeBlock` directive's fenced body and the
+        `language` attribute a bare fence leaves it; the media family's composition; and both
+        table forms, the pipe table's cell split and its named errors. `fenceInfo` is a rule both
+        directions answer alike and moves to the `markdown/` root with the language attribute.
+        **Settled** (the maintainer, 2026-08-27): 1d's last pick, the one
+        `container-block-separation` holds — a CommonMark block and a directive block sit adjacent
+        in a container body with no blank line between them. That reduces the three cases to one
+        rule, separation only where its absence would merge the blocks: the `:::` fence is
+        separation already, and 3c's claim ends the lazy continuation that would otherwise swallow
+        it. The fixture becomes a round-trip pair, and with `nested-list-separation` and 3e's pair
+        that empties `corpus/unspellable/`: this chunk settles the directory's own guard in
+        `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.
+        **Settled** (the maintainer, 2026-09-01): losing that cause closed one of the shapes input
+        accepted and emit refused, not the last. Two adjacent lists of a kind are what
+        `adfToMarkdown` refuses and one `- ` spelling cannot hold apart, and the walk reached them
+        two ways — a marker change, which CommonMark opens a second list on, and an empty last item,
+        whose blank line pops the container the list's identity hung from. The parser opens no list
+        beside one of its own kind instead, the way it already drops the blank lines between items;
+        3k owes the CommonMark suite an exception where the reference HTML holds two `<ul>`. The
+        `normalization/` arm emits each document and reads it back from here, so the population that
+        class lives in is checked rather than read. The README's canonical-fixpoint sentence still
+        claims more than the parser keeps — 3e's three shapes — which stays milestone 5's to
+        narrow.