Answer architecture round 1: 2 🔴, 5 🟡; readableBlock alone fills and reads the spelling memo, the escaper's steps hand on what they claim rather than write a shared buffer, engine-limit names only the throws an engine returns, and the docs agree on it

CHANGELOG.md

@@ -9,9 +9,10 @@
   code. `MIGRATION.md` says which call to take.
 - **Breaking:** the markdown readers refuse a value that is not a string with the new code
   `not-a-string`; `MIGRATION.md` lists what each value did before.
-- **Breaking:** every call returns the new code `engine-limit` where the JavaScript engine runs
-  short of memory or passes its longest array, and, on JavaScriptCore, its longest string. A retry
-  may succeed. Every other refusal stays deterministic.
+- **Breaking:** every call returns the new code `engine-limit` where the JavaScript engine passes
+  its longest array, `Map` or `Set`, or finds no memory for a buffer, and, on JavaScriptCore, where
+  its heap runs short or a string passes its longest. A retry may succeed. Every other refusal stays
+  deterministic.
 - **Breaking:** an attribute value that is not a plain object, array or JSON primitive, such as a
   `Date`, `Map`, typed array or class instance, makes `isAdfDocument` return `false` and the
   converters refuse it as `not-an-adf-document`. Before, the converters wrote it as `{}` or its own

MIGRATION.md

@@ -88,8 +88,8 @@ Markdown the spelling table leaves alone, which `0.2.0` reads as a different doc
 ### Error codes
 
 `unmappable-image`, `unspellable-character`, `unspellable-line-start` and `unspellable-link` leave
-`ConvertErrorCode` and `engine-limit` and `not-a-string` join it: a `switch` naming one of the four
-stops compiling, and one naming every code needs the new cases. A document `adfToMarkdown` refused with one of the
+`ConvertErrorCode`, and `engine-limit` and `not-a-string` join it. A `switch` naming one of the four
+stops compiling, and one naming every code needs the two new cases. A document `adfToMarkdown` refused with one of the
 three `unspellable-` codes now converts in `adfToLosslessMarkdown`; markdown the parser refused
 with one of the four now reads, or refuses with the code the table gives.
 
@@ -114,4 +114,4 @@ with one of the four now reads, or refuses with the code the table gives.
 | `null`, `undefined` or a non-empty array, on parse | throws a `TypeError` | `not-a-string` |
 | a `String` object, on parse | the document its text spells | `not-a-string`; pass `String(value)` |
 | any other value that is not a string, such as a number or `{}`, on parse | an empty document | `not-a-string` |
-| a conversion that runs the JavaScript engine short of memory or past its longest array | throws a `RangeError`, or the engine ends the process | `engine-limit`; retry it once |
+| a conversion past the JavaScript engine's longest array, `Map` or `Set`, or finding no memory for a buffer | throws a `RangeError` | `engine-limit`; retry it once |

README.md

@@ -411,7 +411,9 @@ typed on `ConvertError` takes both.
 A call reports the first refusal in document order and stops, so a document with several surfaces
 them one per call. Every refusal is deterministic — there is no I/O anywhere — so a retry returns
 the identical error: fix the input, or set the document aside. The exception is `engine-limit`,
-whose causes include memory running short: retry it once, and treat a repeat as lasting.
+whose causes include memory running short: retry it once, and treat a repeat as lasting. On V8
+(Node, Deno, Chrome) a heap that runs out ends the process instead, so convert input of unbounded
+size in a worker.
 
 ### Parsing
 
@@ -443,9 +445,9 @@ The emitter raises these, and so does a parse, which asks the emitter how to spe
 
 | Code | Fires when | What you can do |
 | --- | --- | --- |
-| `engine-limit` | in every call: a conversion that passes the longest array the JavaScript engine builds or runs it short of memory, and on JavaScriptCore (Bun, Safari) one that passes its longest string, 2^31 − 1 characters | retry once; if it repeats, writing: set the document aside, keeping the ADF and passing it over or showing it read-only; reading: shorten the markdown, or nest its lists and quotes less deeply |
+| `engine-limit` | in every call: a conversion that passes the longest array, `Map` or `Set` the JavaScript engine builds, or that finds no memory for a buffer; on JavaScriptCore (Bun, Safari), also one that runs its heap short or passes its longest string, 2^31 − 1 characters | retry once; if it repeats, writing: set the document aside, keeping the ADF and passing it over or showing it read-only; reading: shorten the markdown, or nest its lists and quotes less deeply |
 | `unsupported-nesting-depth` | blocks, marks, an attribute's JSON or a carried node's JSON nest past 500 levels | keep the ADF and pass the document over, or show it read-only; flatten the input where you are the one who wrote it |
-| `unsupported-node-shape` | parsing, in `losslessMarkdownToAdf`: markdown spells a node with an attribute, value, argument or body its type does not take, or without one it needs, wraps a directive mark around nothing or only hard breaks, writes as a directive a node or mark the lossless flavour spells as CommonMark, or one that, written out as plain CommonMark, would be longer than 536870888 characters, or puts a reserved directive out of place: `!adf:textBreak{}` parting nothing, `!adf:doc` anywhere but as the whole document. Emitting, in `adfToLosslessMarkdown`: a node not riding the carry that carries one mark type twice, a block or a non-text inline node holding `text`, or a leaf block or a non-text inline node holding `content`. Emitting, in `adfToPortableMarkdown`: a line or task list the portable writer cannot spell, a bug in this library. Emitting, in both writers: a document whose markdown would be longer than 536870888 characters, V8's longest string, on every engine; in `adfToPortableMarkdown`, also a document whose text alone is that long, edge whitespace included. In every call: a conversion that passes the longest string the JavaScript engine builds | fix what the message names; [`spec/flavour.md`](https://github.com/larvit/adf-codec/blob/main/spec/flavour.md) lists every type's attributes and body. For a portable line or task list, report it as a bug. Past 536870888 characters or the engine's longest string, writing: set the document aside, keeping the ADF and passing it over or showing it read-only; reading: shorten the markdown, or nest its lists and quotes less deeply |
+| `unsupported-node-shape` | parsing, in `losslessMarkdownToAdf`: markdown spells a node with an attribute, value, argument or body its type does not take, or without one it needs, wraps a directive mark around nothing or only hard breaks, writes as a directive a node or mark the lossless flavour spells as CommonMark, or one that, written out as plain CommonMark, would be longer than 536870888 characters, or puts a reserved directive out of place: `!adf:textBreak{}` parting nothing, `!adf:doc` anywhere but as the whole document. Emitting, in `adfToLosslessMarkdown`: a node not riding the carry that carries one mark type twice, a block or a non-text inline node holding `text`, or a leaf block or a non-text inline node holding `content`. Emitting, in `adfToPortableMarkdown`: a line or task list the portable writer cannot spell, a bug in this library. Emitting, in both writers: a document whose markdown would be longer than 536870888 characters, V8's longest string, on every engine; in `adfToPortableMarkdown`, also a document whose text alone is that long, edge whitespace included. In every call: a conversion that passes V8's or SpiderMonkey's longest string | fix what the message names; [`spec/flavour.md`](https://github.com/larvit/adf-codec/blob/main/spec/flavour.md) lists every type's attributes and body. For a portable line or task list, report it as a bug. Past 536870888 characters or the engine's longest string, writing: set the document aside, keeping the ADF and passing it over or showing it read-only; reading: shorten the markdown, or nest its lists and quotes less deeply |
 
 ## The guarantees
 
@@ -459,8 +461,7 @@ Serves [Goals](#goals) 1, 4 and 5.
 - Markdown this library reads, and markdown it writes, means what the CommonMark spec says. The
   bullets below name every exception.
 - CommonMark is valid input to `commonMarkToAdf`, apart from the raw HTML `unmappable-html` names,
-  nesting past 500 levels, and input whose conversion passes the longest string or array the
-  JavaScript engine builds.
+  nesting past 500 levels, and input whose conversion `engine-limit` or the length bound refuses.
 - The other readers claim shapes CommonMark reads as text or code. `losslessMarkdownToAdf` claims
   four: literal text matching directive, pipe-table or strikethrough syntax, and a code fence whose
   info string opens `adf:`. `portableMarkdownToAdf` claims what [Portable
@@ -487,7 +488,7 @@ Serves [Goals](#goals) 1, 4 and 5.
   the outer brackets literal text, which the spec requires and the reference itself breaks, nesting
   one `<a>` in the other.
 - Not every document converts back: `adfToLosslessMarkdown` refuses a document nesting past 500
-  levels, and the node shapes the `unsupported-node-shape` row lists. Show the refusal and keep the
+  levels, the node shapes the `unsupported-node-shape` row lists, and what `engine-limit` names. Show the refusal and keep the
   document read-only; saving markdown you could not produce is the loss the round-trip exists to
   stop.
 - The pipe table that `losslessMarkdownToAdf` and `portableMarkdownToAdf` read narrows GFM's twice:

docs/comprehension-history.md

@@ -680,3 +680,34 @@ Maintainability senior, hardest first:
 Inherited architect, would restructure first:
 
 - Locality: `src/markdown/emit/adf-to-markdown.ts:126` `readableBlock`: the memo is mutated and deleted across parse, emit and portable, and the length bound is applied at five sites
+
+## 2026-10-13T14:48:38Z, PR #37 at ecd695a, against 7a27f6b
+
+Ruling: worse
+
+| Seat | Navigation | Locality | Shape | Self-sufficiency | Overall |
+|---|---|---|---|---|---|
+| Mid A | better | worse | better | worse | worse |
+| Inherited architect | better | worse | same | worse | worse |
+
+Mid A, decided by:
+
+- Locality, Self-sufficiency: `src/markdown/emit/adf-to-markdown.ts:116` `commonMarkSpelling` / `readableBlock` / `takeKeptSpelling`: only commonMarkSpelling fills the memo and a read empties it, so whether an entry exists depends on which caller ran first; the reason lives only behind a pointer to docs/decisions.md
+- Locality: `src/markdown/emit/line-escaping.ts:229` `escapeClosedRuns`: both steps write one shared Uint8Array, and correctness rests on the scan order a second comment line must defend
+- Navigation, Shape: `src/markdown/length-bound.ts:30` `withinEngineLimits`: the engine-limit catch moves out of result.ts into one well-named file, with string-length and engine limits apart and `engine-limit` a code of its own
+- Locality: `src/markdown/emit/adf-to-markdown.ts:51` `writeMarkdown` / `walkBlocks` / `commonMarkSpelling`: the length bound is enforced in layers a reader changing it must hold together
+- Shape: `src/markdown/parse/markdown-to-adf.ts:266` `directiveNode`: undefined is wrapped into a Result to pass the engine guard, then unpicked
+- Shape: `src/markdown/emit/line-escaping.ts:35` `Escapings`: the type is a lookup function, its comment describes the Uint8Array behind it; `backslashed` adds 4096-piece chunking
+- Shape, Locality: `src/canonical-json.ts:23` `canonicalJsonPieces`: a generator replaces a boolean-continue callback
+- Shape: `src/markdown/emit/inline-line.ts:235` `emitLeaf`: the content-or-text refusal moves into one place
+- Locality: `src/markdown/portable/adf-to-portable-markdown.ts:128` `portableSequence`: a spelling refusal propagates where it was swallowed, at the cost of Sourced path plumbing
+
+Inherited architect, decided by:
+
+- Locality, Self-sufficiency: `src/markdown/emit/adf-to-markdown.ts:139` `takeKeptSpelling`: reading deletes the entry and only commonMarkSpelling fills it, so readableBlock is right only if another file's caller asked first, once per node; explained only by a pointer to docs/decisions.md
+- Locality, Shape: `src/markdown/parse/markdown-to-adf.ts:266` `directiveNode`: a second withinEngineLimits inside readDocument's, fed `?? success(undefined)`, so null and undefined carry meaning the reader must remember
+- Locality: `src/markdown/emit/adf-to-markdown.ts:58` `walkBlocks`: the length bound is enforced at about six sites across three files
+- Navigation: `src/markdown/length-bound.ts:30` `withinEngineLimits`: engine-limit handling sits in a file named for it, and the engine-limit code parts memory from the length bound
+- Shape, Locality: `src/markdown/emit/line-escaping.ts:229` `escapeClosedRuns`: mutates its input in place and needs a two-line comment arguing it is safe; output joined in batches of 4096
+- Locality, Shape: `src/markdown/portable/adf-to-portable-markdown.ts:128` `portableSequence`: a refusal propagates with its source path, where it was swallowed
+- Shape: `src/markdown/emit/inline-line.ts:235` `emitLeaf`: one place refuses content and text, and a generator replaces the boolean-callback JSON writer

docs/decisions.md

@@ -467,11 +467,11 @@ handles one cause alike whichever node, attribute or direction raised it.
   causes the bound (§The code list). A carried node passes it on about 1 MB of deeply nested JSON,
   since the block carry indents two spaces a level; `todo.md` item 107 respells the carry in a
   length linear in its JSON (2026-10-11).
-- A conversion the engine stops, by running short of memory or passing its longest array, is
-  `engine-limit`, at the empty path. A retry may pass it, so `unsupported-node-shape`, which never
-  does, cannot hold it. JavaScriptCore throws the same `Out of memory` past its longest string,
-  which takes `engine-limit` too: telling the two apart would mean reading the engine's message
-  (2026-10-13, the maintainer).
+- A conversion the engine stops with a throw of its own, past its longest array, `Map` or `Set`
+  or short of memory, is `engine-limit`, at the empty path. A retry may pass the memory case, so
+  `unsupported-node-shape`, which no retry passes, cannot hold the class. JavaScriptCore throws the
+  same `Out of memory` past its longest string, which takes `engine-limit` too, since only the
+  message would tell the two apart (2026-10-13, the maintainer).
 - The markdown readers and `htmlToAdf` refuse a value that is not a string as `not-a-string`, at
   position `{ line: 1, offset: 0 }` with an empty path: no existing code reads true of it, and
   `not-an-adf-document` names the emitters' input (2026-10-05).

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

@@ -108,39 +108,34 @@ function interruptsParagraph(node: AdfNode): boolean {
 function emitBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> {
   const model = blockNodeModel(node.type)
   if (model === undefined) return carriedFence(carriedBlock(node, path, depth))
-  const readable = readableBlock(node, path, depth, writing)
+  const readable = readableBlock(node, path, depth, writing, false)
   if (readable !== undefined) return readable
   return emitDirectiveBlock(node, model, path, depth, () => walkBlocks(nodeContent(node), path, depth + 1, writing))
 }
 
 export function commonMarkSpelling(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing & { memo: SpellingMemo }): Result<null> | undefined {
-  const readable = readableBlock(node, path, depth, writing)
-  if (readable === undefined) {
-    writing.memo.set(node, { block: undefined, depth })
-    return undefined
-  }
+  const readable = readableBlock(node, path, depth, writing, true)
+  if (readable === undefined) return undefined
   if (!readable.ok) return readable
   const fits = withinLongest(readable.value.text)
   if (!fits.ok) return fits
-  writing.memo.set(node, { block: readable.value, depth })
   return readable.value.spelling === 'directive' ? undefined : success(null)
 }
 
-function readableBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> | undefined {
-  const kept = takeKeptSpelling(writing.memo, node)
+// Only an asked node's spelling is kept, and reading it drops it: the walk above spells the node into its own text, so no level of a subtree holds that text twice.
+function readableBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing, asked: boolean): Result<EmittedBlock> | undefined {
+  const { memo } = writing
+  const kept = memo?.get(node)
+  memo?.delete(node)
   if (kept !== undefined) {
     if (kept.block === undefined) return undefined
     // An entry holds the spelling at its fill depth. A read at or above it rebases headroom; a read below re-spells, because a hit skips the walk's depth guards.
     if (depth <= kept.depth) return success({ ...kept.block, headroom: kept.block.headroom + kept.depth - depth })
   }
-  return spellReadableBlock(node, path, depth, writing)
-}
-
-// docs/decisions.md §The spelling memo
-function takeKeptSpelling(memo: SpellingMemo | undefined, node: AdfNode): KeptSpelling | undefined {
-  const kept = memo?.get(node)
-  memo?.delete(node)
-  return kept
+  const spelled = spellReadableBlock(node, path, depth, writing)
+  if (asked && spelled === undefined) memo?.set(node, { block: undefined, depth })
+  if (asked && spelled?.ok === true) memo?.set(node, { block: spelled.value, depth })
+  return spelled
 }
 
 function spellReadableBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> | undefined {

src/markdown/emit/line-escaping.ts

@@ -11,7 +11,7 @@ import { opensLinkDefinition } from '../commonmark/link-reference-definitions.ts
 export type DelimiterRole = 'close' | 'open'
 
 // A segment's kind: `backslash` text, `bracketed` text inside `[…]` (link text, alt, a directive's content), `bracketed-link-target` syntax: a link target inside `[…]`, `none` syntax written as is.
-export type InlineEscaping = 'backslash' | 'bracketed' | 'bracketed-link-target' | 'none'
+export type InlineEscaping = (typeof escapingCodes)[number]
 
 export type NodeRange = { first: number; last: number }
 
@@ -32,9 +32,14 @@ type EmittedDelimiter = { closes: boolean; offset: number; pair: number; width:
 
 type EmittedRun = { canClose: boolean; canOpen: boolean; character: string; delimiters: EmittedDelimiter[]; length: number; start: number }
 
-// One byte a character, never an array element or Set entry: a line may run to hundreds of millions of characters.
 type Escapings = (index: number) => InlineEscaping | undefined
 
+// Where a segment's first character landed in the output.
+type PlacedSegment = { segment: InlineSegment; start: number }
+
+// The run's escapable characters, or its characters before `end`.
+type RunEscapes = { end: number; escapable: false } | { escapable: true }
+
 type EscapeWalk = {
   readonly claims: Claims
   readonly container: LineContainer
@@ -44,7 +49,7 @@ type EscapeWalk = {
   readonly scan: string
 }
 
-const escapingCodes: readonly InlineEscaping[] = ['backslash', 'bracketed', 'bracketed-link-target', 'none']
+const escapingCodes: readonly ['backslash', 'bracketed', 'bracketed-link-target', 'none'] = ['backslash', 'bracketed', 'bracketed-link-target', 'none']
 
 const followsLinkText = /[([]/
 
@@ -85,6 +90,7 @@ function resolveEmphasis(segments: readonly InlineSegment[]): InlineSegment[] {
 
 function escape(segments: readonly InlineSegment[], container: LineContainer, claims: Claims): AssembledLine {
   const scan = segments.map((segment) => segment.text).join('')
+  // One byte a character, never an array element or Set entry: a line may run to hundreds of millions of characters.
   const codes = new Uint8Array(scan.length)
   let start = 0
   for (const segment of segments) {
@@ -96,16 +102,15 @@ function escape(segments: readonly InlineSegment[], container: LineContainer, cl
     return code === undefined ? undefined : escapingCodes[code]
   }
   const escaped = escapeClosedRuns(scan, escapings, escapeClaims(scan, escapings, container, claims))
-  const { output, placements } = backslashed(segments, scan, escaped)
+  const { output, placed } = backslashed(segments, scan, escaped)
   if (container === 'paragraph' && opensLinkDefinition(output)) {
     if (segments[0]?.nodes !== undefined) return { line: output, openingLinkAsDirective: true, unspellableRuns: [] }
-    return { line: `\\${output}`, unspellableRuns: unspellableRuns(segments, output, placements) }
+    return { line: `\\${output}`, unspellableRuns: unspellableRuns(placed, output) }
   }
-  return { line: output, unspellableRuns: unspellableRuns(segments, output, placements) }
+  return { line: output, unspellableRuns: unspellableRuns(placed, output) }
 }
 
-// The output, and where each segment's first character landed in it.
-function backslashed(segments: readonly InlineSegment[], scan: string, escaped: Uint8Array): { output: string; placements: number[] } {
+function backslashed(segments: readonly InlineSegment[], scan: string, escaped: Uint8Array): { output: string; placed: PlacedSegment[] } {
   // Joined a few thousand pieces at a time: an array element per escape would cost more than the character it escapes.
   const chunks: string[] = []
   let pieces: string[] = []
@@ -119,7 +124,7 @@ function backslashed(segments: readonly InlineSegment[], scan: string, escaped:
   }
   pieces.push(scan.slice(from))
   chunks.push(pieces.join(''))
-  const placements: number[] = []
+  const placed: PlacedSegment[] = []
   let escapes = 0
   let next = escaped.indexOf(1)
   let start = 0
@@ -128,10 +133,10 @@ function backslashed(segments: readonly InlineSegment[], scan: string, escaped:
       escapes += 1
       next = escaped.indexOf(1, next + 1)
     }
-    placements.push(start + escapes)
+    placed.push({ segment, start: start + escapes })
     start += segment.text.length
   }
-  return { output: chunks.join(''), placements }
+  return { output: chunks.join(''), placed }
 }
 
 function escapeClaims(scan: string, escapings: Escapings, container: LineContainer, claims: Claims): Uint8Array {
@@ -150,7 +155,9 @@ function escapeClaims(scan: string, escapings: Escapings, container: LineContain
     while (index > line.start + line.text.length) line = scanLine(scan, line.start + line.text.length + 1)
     if (runCharacters.includes(scan.charAt(index))) {
       const end = index + runLength(scan, index)
-      runEscapes(walk, index, end, line, escaped)
+      const run = runEscapes(walk, index, end, line)
+      if (!run.escapable) escaped.fill(1, index, run.end)
+      else for (let at = index; at < end; at += 1) if (isEscapable(escapings(at))) escaped[at] = 1
       index = end
       continue
     }
@@ -164,18 +171,13 @@ function escapeClaims(scan: string, escapings: Escapings, container: LineContain
 }
 
 // A text character beside one of the emitter's delimiters would lengthen that delimiter's run, so every text character in such a run escapes.
-function runEscapes(walk: EscapeWalk, start: number, end: number, line: ScanLine, escaped: Uint8Array): void {
+function runEscapes(walk: EscapeWalk, start: number, end: number, line: ScanLine): RunEscapes {
   const { escapings, scan } = walk
-  if (runHolds(escapings, start, end, isSyntax) && runHolds(escapings, start, end, isEscapable)) {
-    for (let index = start; index < end; index += 1) if (isEscapable(escapings(index))) escaped[index] = 1
-    return
-  }
-  for (let index = start; index < end; index += 1) {
-    // A backtick run escapes whole: a bare rest would be a shorter backtick string, which can close a span an earlier run opens.
-    const claimed = (index > start && scan.charAt(index) === '`') || claimsRunRest(walk, index, end, line)
-    if (!claimed) break
-    escaped[index] = 1
-  }
+  if (runHolds(escapings, start, end, isSyntax) && runHolds(escapings, start, end, isEscapable)) return { escapable: true }
+  let index = start
+  // A backtick run escapes whole: a bare rest would be a shorter backtick string, which can close a span an earlier run opens.
+  while (index < end && ((index > start && scan.charAt(index) === '`') || claimsRunRest(walk, index, end, line))) index += 1
+  return { end: index, escapable: false }
 }
 
 function runHolds(escapings: Escapings, start: number, end: number, kind: (escaping: InlineEscaping | undefined) => boolean): boolean {
@@ -225,8 +227,8 @@ function claimsCharacter({ container, escapings, headingCloser, linkClose, scan
 }
 
 // CommonMark reads no escape inside a code span, so a backtick string left beside an escape still closes a span that an earlier bare run of its length opens.
-// The walk runs backwards and escapes only the run it just read, so every index it reads still holds the claims alone.
-function escapeClosedRuns(scan: string, escapings: Escapings, escaped: Uint8Array): Uint8Array {
+function escapeClosedRuns(scan: string, escapings: Escapings, claimed: Uint8Array): Uint8Array {
+  const escaped = claimed.slice()
   // The lengths of the backtick strings escapes leave: a bare run of one of these lengths would open a span one of them closes, so it is escaped too.
   const formed = new Set<number>()
   let end = scan.length - 1
@@ -239,11 +241,11 @@ function escapeClosedRuns(scan: string, escapings: Escapings, escaped: Uint8Arra
     while (scan.charAt(start - 1) === '`') start -= 1
     let segmentEnd = end
     for (let index = end; index > start; index -= 1) {
-      if (escaped[index] !== 1) continue
+      if (claimed[index] !== 1) continue
       formed.add(segmentEnd - index + 1)
       segmentEnd = index - 1
     }
-    if (segmentEnd !== end || escaped[start] === 1) formed.add(segmentEnd - start + 1)
+    if (segmentEnd !== end || claimed[start] === 1) formed.add(segmentEnd - start + 1)
     else if (escapings(start) !== 'none' && formed.has(end - start + 1)) {
       escaped.fill(1, start, end + 1)
       // Each escaped backtick then stands alone, a string of length one.
@@ -255,18 +257,17 @@ function escapeClosedRuns(scan: string, escapings: Escapings, escaped: Uint8Arra
 }
 
 // One emphasis run, the innermost, or every highlight run the line cannot spell.
-function unspellableRuns(segments: readonly InlineSegment[], output: string, placements: readonly number[]): MarkRun[] {
-  const { nodes, runs } = emittedRuns(segments, placements, output)
+function unspellableRuns(placed: readonly PlacedSegment[], output: string): MarkRun[] {
+  const { nodes, runs } = emittedRuns(placed, output)
   const pair = misflanked(runs) ?? unpaired(runs)
   const run = pair === undefined ? undefined : nodes[pair]
-  return run === undefined ? unreadHighlights(segments, output, placements) : [run]
+  return run === undefined ? unreadHighlights(placed, output) : [run]
 }
 
 // No `==` in text can open or close, and highlights never nest, so a pair reads back where each delimiter flanks.
-function unreadHighlights(segments: readonly InlineSegment[], output: string, placements: readonly number[]): MarkRun[] {
+function unreadHighlights(placed: readonly PlacedSegment[], output: string): MarkRun[] {
   const unread: MarkRun[] = []
-  for (const [index, segment] of segments.entries()) {
-    const start = placements[index] ?? 0
+  for (const { segment, start } of placed) {
     if (segment.highlight === undefined) continue
     const flanking = highlightFlanking(output, start)
     const flanks = segment.highlight === 'open' ? flanking.opens : flanking.closes
@@ -305,12 +306,11 @@ function delimiterAt(run: EmittedRun, closes: boolean, offset: number, width: nu
   return run.delimiters.find((delimiter) => delimiter.closes === closes && delimiter.offset === offset && delimiter.width === width)
 }
 
-function emittedRuns(segments: readonly InlineSegment[], placements: readonly number[], output: string): { nodes: MarkRun[]; runs: EmittedRun[] } {
+function emittedRuns(placed: readonly PlacedSegment[], output: string): { nodes: MarkRun[]; runs: EmittedRun[] } {
   const runs: EmittedRun[] = []
   const nodes: MarkRun[] = []
   const open: number[] = []
-  for (const [index, segment] of segments.entries()) {
-    const start = placements[index] ?? 0
+  for (const { segment, start } of placed) {
     if (segment.emphasis === undefined) continue
     const closes = segment.emphasis === 'close'
     const pair = closes ? (open.pop() ?? nodes.length) : nodes.length

src/markdown/length-bound.test.ts

@@ -36,6 +36,9 @@ test('refuses a string past the bound as too long on every engine, and any other
   }
   assert.equal(code('Invalid array length'), 'engine-limit')
   assert.equal(code('Array buffer allocation failed'), 'engine-limit')
+  assert.equal(code('Map maximum size exceeded'), 'engine-limit')
+  assert.equal(code('Set maximum size exceeded'), 'engine-limit')
+  assert.equal(code('invalid array length'), 'engine-limit')
   assert.deepEqual(
     withinEngineLimits(() => success('x')),
     { ok: true, value: 'x' },

src/markdown/length-bound.ts

@@ -3,9 +3,16 @@ import { failure, success, type Result } from '../result.ts'
 // V8's longest string (docs/decisions.md §Markdown past V8's longest string is refused on every engine).
 export const longestMarkdown = 2 ** 29 - 24
 
-// Measured on Firefox 155, Node 24 and Bun 1.4. SpiderMonkey's overflow and V8's string overflow both mean a string past longestMarkdown; the others name an engine's own limit or its memory running short.
+// Measured on Firefox 155, Node 24 and Bun 1.4, and SpiderMonkey's array length from its js.msg. SpiderMonkey's overflow and V8's string overflow both mean a string past longestMarkdown; the others name an engine's own limit or its memory running short.
 const pastLongestString = ['InternalError: allocation size overflow', 'RangeError: Invalid string length']
-const pastEngineLimit = ['RangeError: Array buffer allocation failed', 'RangeError: Invalid array length', 'RangeError: Out of memory']
+const pastEngineLimit = [
+  'RangeError: Array buffer allocation failed',
+  'RangeError: Invalid array length',
+  'RangeError: Map maximum size exceeded',
+  'RangeError: Out of memory',
+  'RangeError: Set maximum size exceeded',
+  'RangeError: invalid array length',
+]
 
 export function tooLong<T>(): Result<T> {
   return failure('unsupported-node-shape', `the markdown for this document, or for a directive's plain CommonMark, would be longer than ${longestMarkdown} characters, the longest this library writes`, [])

todo.md

@@ -32,7 +32,6 @@
 | 89 | 0.2.1 |  | **Build a `date`, `emoji`, `inlineCard`, `mention` or `status` holding no mark Atlassian's schema withholds from it, in every reader.** | 4 | 4 | 5 | 6 | 4 | 13.0 |
 | 99 | 0.2.1 | defect | **Write a linked external image standing inline or in a table cell in the spelling a reader panel picks, in `adfToPortableMarkdown`.** | 3 | 3 | 6 | 7 | 7 | 12.9 |
 | 100 | 0.2.1 | decision | **Put the reading of an image's title as its caption back to a reader panel, now that a writer panel reads a title as hover text.** | 3 | 3 | 4 | 5 | 4, 6 | 10.9 |
-| 110 | 0.2.1 | decision | **Fill and read the spelling memo in `readableBlock` alone, dropping a spelled node's children's entries so memory stays linear.** | 3 | 3 | 2 | 6 | 2 | 10.9 |
 | 60 | 0.2.1 | decision | **Collect the questions `parse/` asks `emit/` into one named module.** | 3 | 4 | 2 | 6 | 2 | 10.7 |
 | 59 | 0.2.1 | decision | **Group the directive grammar into `src/markdown/directive/`, move `Read<T>` to `result.ts`, and move `Flavour` and `flavourClaims` to `markdown/flavour.ts`.** | 3 | 5 | 2 | 6 | 2 | 10.4 |
 | 62 | 0.2.1 | decision | **Move the portable flavour's reading out of `parse/` and its writing out of `emit/` into `markdown/portable/`, so `emit/` no longer imports `portable/`.** | 4 | 5 | 2 | 6 | 2 | 9.4 |
@@ -126,16 +125,6 @@ Every reader reads `![a](u "t")` as an image captioned `t` (`docs/decisions.md`
 image only alone in its paragraph, 3 of 3 on 2026-10-09). On 2026-10-11 a writer panel of the same
 audience kept the captioned image's `!adf:caption` directive, 3 of 3, reading a title as hover text.
 
-### 110. Fill and read the spelling memo in `readableBlock` alone, dropping a spelled node's children's entries so memory stays linear.
-
-Item 106 made the CommonMark ask fill the memo and the walk above drop each entry as it reads it, so
-a deep subtree holds no level's text twice. Every comprehension seat read that split, across
-`commonMarkSpelling`, `readableBlock` and their three callers, as order-dependent state, and the
-chunk shipped under a worse ruling on Locality. Give the memo one reader and writer again: when
-`readableBlock` keeps a node's spelling, it drops the entries of the node's children and
-grandchildren, since the node's own spelling now holds their text. Found by the comprehension check
-of item 106, 2026-10-13.
-
 ### 60. Collect the questions `parse/` asks `emit/` into one named module.
 
 `parse/` asks `emit/` through `commonMarkSpelling` and `openingLinkTakesDirective`, each imported