AGENTS.md

@@ -17,8 +17,10 @@ When losslessness and readability conflict, losslessness wins.
 
 The other direction is a canonical fixpoint, not byte-identity: human markdown normalizes, the way
 back yields the library's canonical spelling, and that spelling round-trips byte-identically —
-where there is a way back. CommonMark spells link destinations the flavour has no escape for, so a
+where there is a way back. CommonMark spells some things the flavour has no escape for — a link
-parse succeeding does not imply a spellable document; `todo.md` 3k's exception list names those.
+destination or title holding a backslash or newline, a paragraph opening with a code span whose
+backticks read back as a fence — so a parse succeeding does not imply a spellable document;
+`corpus/commonmark-spec/exceptions.json` names those.
 
 "Equals" is structural equality over editor-normal ADF — adjacent text nodes with identical marks
 merged, JSON number semantics, an empty attrs object, marks array or content array the absent
@@ -57,8 +59,12 @@ Round-trip equality is a property tested over a corpus, not a claim made in pros
 why ~20 lines of own code cannot do the job, who maintains it, and what auditing it costs. So the
 CommonMark and HTML parsers are written in this repo. A table a standard fixes is data rather than
 a dependency: HTML5's 2125 semicolon-terminated character references ship packed in their own
-module, so entity decoding is complete without one. `devDependencies`: few, each earning its keep;
+module, so entity decoding is complete without one. The CommonMark spec suite is the same shape of
-they never reach a consumer.
+data and ships vendored at `corpus/commonmark-spec/` rather than as the `commonmark-spec` dev
+dependency — that package is CommonJS-only, and Renovate auto-bumping a spec version would silently
+point the vendored exception list's example numbers at a renumbered suite. A spec bump is a
+deliberate re-pin, exceptions re-derived by hand beside it. `devDependencies`: few, each earning its
+keep; they never reach a consumer.
 
 ## 6. The package contract
 
@@ -198,7 +204,8 @@ resolver maps them, under `NodeNext` alone; a `.d.ts` reader that is not `tsc` s
 `node-floor.js` round-trips the installed package under a Node pinned to `engines.node`'s floor.
 
 A fourth engine reads the build rather than the source: a headless Firefox loads `dist/index.js`
-over HTTP and converts the whole corpus, which is §6's browser half and the only SpiderMonkey
+over HTTP and converts the round-trip, normalization and error fixtures — the `commonmark-spec`
+sort is the Node suite's to check — which is §6's browser half and the only SpiderMonkey
 there is — the gate's other three engines are two V8s and a JavaScriptCore that is not Safari's.
 A WebDriver session is what carries a verdict back out, the driver and the page's server sharing
 one network namespace so each is the other's `127.0.0.1`; `--headless --screenshot` has no such

browser-tests/run.js

@@ -72,6 +72,7 @@ assert.deepEqual(
   readdirSync(corpusRoot, { withFileTypes: true })
     .filter((entry) => entry.isDirectory())
     .map((entry) => entry.name)
+    .filter((name) => name !== 'commonmark-spec')
     .sort(),
   ['errors', 'normalization', 'round-trip'],
   'a corpus kind the browser leg does not convert',

corpus/README.md

@@ -12,5 +12,13 @@ One directory per contract kind, each landing with its milestone:
   pins which error.
 - `real-payloads/` — `<name>.json`: sanitized live ADF, round-tripped ADF→markdown→ADF. No
   expected markdown.
+- `commonmark-spec/` — the CommonMark suite run against `markdownToAdf` by three checks. `spec.json`
+  is the suite; `refusals.json` pins each refusing example to its error `code`; `exceptions.json`
+  pins each known divergence by `check`, `example`, `kind` and the exact `divergence`, with a
+  `reason`. `kind` is `mark-model` (the permanent count divergence from ADF's mark-per-text-node
+  model), `unspellable` (parses but the flavour has no spelling) or `pending` (a parser gap a later
+  milestone may close).
 
-JSON is editor-normal (AGENTS.md §2), two-space indent, keys sorted.
+JSON is editor-normal (AGENTS.md §2), two-space indent, keys sorted. `spec.json` is the vendored,
+upstream machine-readable suite, byte-exact (CommonMark 0.31.2, CC-BY-SA-4.0, © John MacFarlane),
+and is not re-serialized by the corpus gate.

corpus/commonmark-spec/exceptions.json

@@ -0,0 +1,436 @@
+[
+  {
+    "check": "fixpoint",
+    "divergence": "unspellable-link",
+    "example": 196,
+    "kind": "unspellable",
+    "reason": "The link title holds literal newlines no escape spells."
+  },
+  {
+    "check": "fixpoint",
+    "divergence": "unspellable-link",
+    "example": 202,
+    "kind": "unspellable",
+    "reason": "The link destination holds a backslash the flavour cannot escape."
+  },
+  {
+    "check": "count",
+    "divergence": "ul 2/1",
+    "example": 301,
+    "kind": "pending",
+    "reason": "A list continuing past a marker change renders as two lists, the parser opens one."
+  },
+  {
+    "check": "count",
+    "divergence": "ol 2/1",
+    "example": 302,
+    "kind": "pending",
+    "reason": "A list continuing past a marker change renders as two lists, the parser opens one."
+  },
+  {
+    "check": "fixpoint",
+    "divergence": "unspellable-line-start",
+    "example": 330,
+    "kind": "unspellable",
+    "reason": "A paragraph opens with a code span whose backticks read back as a fence."
+  },
+  {
+    "check": "fixpoint",
+    "divergence": "unspellable-line-start",
+    "example": 331,
+    "kind": "unspellable",
+    "reason": "A paragraph opens with a code span whose backticks read back as a fence."
+  },
+  {
+    "check": "fixpoint",
+    "divergence": "unspellable-line-start",
+    "example": 340,
+    "kind": "unspellable",
+    "reason": "A paragraph opens with a code span whose backticks read back as a fence."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/1",
+    "example": 369,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/1",
+    "example": 373,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 2/1",
+    "example": 389,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3",
+    "example": 393,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/5",
+    "example": 394,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/3",
+    "example": 395,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3",
+    "example": 399,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 404,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3",
+    "example": 406,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/1",
+    "example": 407,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/1",
+    "example": 408,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/1",
+    "example": 409,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3",
+    "example": 410,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3",
+    "example": 411,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 413,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 414,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 415,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 3/1",
+    "example": 417,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/5 strong 1/3",
+    "example": 418,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/2",
+    "example": 422,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/3",
+    "example": 424,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 2/1",
+    "example": 425,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 2/1",
+    "example": 426,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 2/1",
+    "example": 427,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/3",
+    "example": 428,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/3",
+    "example": 429,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/2",
+    "example": 430,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/2",
+    "example": 431,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3 strong 2/5",
+    "example": 432,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 1/2",
+    "example": 433,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/1",
+    "example": 461,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 2/1",
+    "example": 463,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 2/1",
+    "example": 464,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 2/1",
+    "example": 465,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 3/1",
+    "example": 466,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "strong 2/1",
+    "example": 468,
+    "kind": "mark-model",
+    "reason": "CommonMark nests same-kind elements; the single mark collapses them to one."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3",
+    "example": 470,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 478,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 479,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/0",
+    "example": 484,
+    "kind": "pending",
+    "reason": "An empty link text stays literal text; CommonMark renders an empty link."
+  },
+  {
+    "check": "text",
+    "divergence": "\"\" against \"[](./target.md)\"",
+    "example": 484,
+    "kind": "pending",
+    "reason": "An empty link text stays literal text; CommonMark renders an empty link."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/0",
+    "example": 487,
+    "kind": "pending",
+    "reason": "An empty link text stays literal text; CommonMark renders an empty link."
+  },
+  {
+    "check": "text",
+    "divergence": "\"\" against \"[]()\"",
+    "example": 487,
+    "kind": "pending",
+    "reason": "An empty link text stays literal text; CommonMark renders an empty link."
+  },
+  {
+    "check": "fixpoint",
+    "divergence": "unspellable-link",
+    "example": 502,
+    "kind": "unspellable",
+    "reason": "The link destination holds a backslash the flavour cannot escape."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/5 em 1/4",
+    "example": 516,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/3",
+    "example": 519,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/5 em 1/4",
+    "example": 530,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 533,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/0",
+    "example": 540,
+    "kind": "pending",
+    "reason": "The case-folding shortcut reference is unresolved; CommonMark folds case and links."
+  },
+  {
+    "check": "text",
+    "divergence": "\"ẞ\" against \"[ẞ]\"",
+    "example": 540,
+    "kind": "pending",
+    "reason": "A case-folding shortcut reference is unresolved; CommonMark folds case and links."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/2",
+    "example": 554,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/2",
+    "example": 558,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "a 1/2",
+    "example": 559,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 638,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  },
+  {
+    "check": "count",
+    "divergence": "em 1/2",
+    "example": 639,
+    "kind": "mark-model",
+    "reason": "The mark spans adjacent text nodes, counted once per node where CommonMark nests one element."
+  }
+]

corpus/commonmark-spec/refusals.json

@@ -0,0 +1,346 @@
+[
+  {
+    "code": "unmappable-html",
+    "example": 21
+  },
+  {
+    "code": "unmappable-html",
+    "example": 31
+  },
+  {
+    "code": "unmappable-html",
+    "example": 148
+  },
+  {
+    "code": "unmappable-html",
+    "example": 149
+  },
+  {
+    "code": "unmappable-html",
+    "example": 150
+  },
+  {
+    "code": "unmappable-html",
+    "example": 151
+  },
+  {
+    "code": "unmappable-html",
+    "example": 152
+  },
+  {
+    "code": "unmappable-html",
+    "example": 153
+  },
+  {
+    "code": "unmappable-html",
+    "example": 154
+  },
+  {
+    "code": "unmappable-html",
+    "example": 155
+  },
+  {
+    "code": "unmappable-html",
+    "example": 156
+  },
+  {
+    "code": "unmappable-html",
+    "example": 157
+  },
+  {
+    "code": "unmappable-html",
+    "example": 158
+  },
+  {
+    "code": "unmappable-html",
+    "example": 159
+  },
+  {
+    "code": "unmappable-html",
+    "example": 160
+  },
+  {
+    "code": "unmappable-html",
+    "example": 161
+  },
+  {
+    "code": "unmappable-html",
+    "example": 162
+  },
+  {
+    "code": "unmappable-html",
+    "example": 163
+  },
+  {
+    "code": "unmappable-html",
+    "example": 164
+  },
+  {
+    "code": "unmappable-html",
+    "example": 165
+  },
+  {
+    "code": "unmappable-html",
+    "example": 166
+  },
+  {
+    "code": "unmappable-html",
+    "example": 167
+  },
+  {
+    "code": "unmappable-html",
+    "example": 168
+  },
+  {
+    "code": "unmappable-html",
+    "example": 169
+  },
+  {
+    "code": "unmappable-html",
+    "example": 170
+  },
+  {
+    "code": "unmappable-html",
+    "example": 171
+  },
+  {
+    "code": "unmappable-html",
+    "example": 172
+  },
+  {
+    "code": "unmappable-html",
+    "example": 173
+  },
+  {
+    "code": "unmappable-html",
+    "example": 174
+  },
+  {
+    "code": "unmappable-html",
+    "example": 175
+  },
+  {
+    "code": "unmappable-html",
+    "example": 176
+  },
+  {
+    "code": "unmappable-html",
+    "example": 177
+  },
+  {
+    "code": "unmappable-html",
+    "example": 178
+  },
+  {
+    "code": "unmappable-html",
+    "example": 179
+  },
+  {
+    "code": "unmappable-html",
+    "example": 180
+  },
+  {
+    "code": "unmappable-html",
+    "example": 181
+  },
+  {
+    "code": "unmappable-html",
+    "example": 182
+  },
+  {
+    "code": "unmappable-html",
+    "example": 183
+  },
+  {
+    "code": "unmappable-html",
+    "example": 184
+  },
+  {
+    "code": "unmappable-html",
+    "example": 185
+  },
+  {
+    "code": "unmappable-html",
+    "example": 186
+  },
+  {
+    "code": "unmappable-html",
+    "example": 187
+  },
+  {
+    "code": "unmappable-html",
+    "example": 188
+  },
+  {
+    "code": "unmappable-html",
+    "example": 189
+  },
+  {
+    "code": "unmappable-html",
+    "example": 190
+  },
+  {
+    "code": "unmappable-html",
+    "example": 191
+  },
+  {
+    "code": "unmappable-html",
+    "example": 201
+  },
+  {
+    "code": "unmappable-html",
+    "example": 308
+  },
+  {
+    "code": "unmappable-html",
+    "example": 309
+  },
+  {
+    "code": "unmappable-html",
+    "example": 344
+  },
+  {
+    "code": "unmappable-html",
+    "example": 475
+  },
+  {
+    "code": "unmappable-html",
+    "example": 476
+  },
+  {
+    "code": "unmappable-html",
+    "example": 477
+  },
+  {
+    "code": "unmappable-html",
+    "example": 491
+  },
+  {
+    "code": "unmappable-html",
+    "example": 494
+  },
+  {
+    "code": "unmappable-image",
+    "example": 517
+  },
+  {
+    "code": "unmappable-html",
+    "example": 524
+  },
+  {
+    "code": "unmappable-image",
+    "example": 531
+  },
+  {
+    "code": "unmappable-html",
+    "example": 536
+  },
+  {
+    "code": "unmappable-image",
+    "example": 572
+  },
+  {
+    "code": "unmappable-image",
+    "example": 573
+  },
+  {
+    "code": "unmappable-image",
+    "example": 576
+  },
+  {
+    "code": "unmappable-image",
+    "example": 577
+  },
+  {
+    "code": "unmappable-image",
+    "example": 579
+  },
+  {
+    "code": "unmappable-image",
+    "example": 584
+  },
+  {
+    "code": "unmappable-image",
+    "example": 585
+  },
+  {
+    "code": "unmappable-image",
+    "example": 586
+  },
+  {
+    "code": "unmappable-image",
+    "example": 587
+  },
+  {
+    "code": "unmappable-image",
+    "example": 588
+  },
+  {
+    "code": "unmappable-image",
+    "example": 589
+  },
+  {
+    "code": "unmappable-image",
+    "example": 591
+  },
+  {
+    "code": "unmappable-html",
+    "example": 613
+  },
+  {
+    "code": "unmappable-html",
+    "example": 614
+  },
+  {
+    "code": "unmappable-html",
+    "example": 615
+  },
+  {
+    "code": "unmappable-html",
+    "example": 616
+  },
+  {
+    "code": "unmappable-html",
+    "example": 617
+  },
+  {
+    "code": "unmappable-html",
+    "example": 623
+  },
+  {
+    "code": "unmappable-html",
+    "example": 625
+  },
+  {
+    "code": "unmappable-html",
+    "example": 626
+  },
+  {
+    "code": "unmappable-html",
+    "example": 627
+  },
+  {
+    "code": "unmappable-html",
+    "example": 628
+  },
+  {
+    "code": "unmappable-html",
+    "example": 629
+  },
+  {
+    "code": "unmappable-html",
+    "example": 630
+  },
+  {
+    "code": "unmappable-html",
+    "example": 631
+  },
+  {
+    "code": "unmappable-html",
+    "example": 642
+  },
+  {
+    "code": "unmappable-html",
+    "example": 643
+  }
+]

src/commonmark-spec.test.ts

@@ -0,0 +1,340 @@
+import assert from 'node:assert/strict'
+import { createHash } from 'node:crypto'
+import { readFileSync } from 'node:fs'
+import { dirname, join } from 'node:path'
+import test from 'node:test'
+import { fileURLToPath } from 'node:url'
+
+import type { AdfDocument, AdfNode } from './adf/document.ts'
+import { adfToMarkdown } from './markdown/emit/adf-to-markdown.ts'
+import { markdownToAdf } from './markdown/parse/markdown-to-adf.ts'
+
+const root = join(dirname(fileURLToPath(import.meta.url)), '..', 'corpus', 'commonmark-spec')
+const checks = ['count', 'fixpoint', 'text'] as const
+
+type Check = (typeof checks)[number]
+type ExceptionKind = 'mark-model' | 'pending' | 'unspellable'
+
+type SpecExample = { example: number; html: string; markdown: string; section: string }
+
+type Exception = { check: Check; divergence: string; example: number; kind: ExceptionKind; reason: string }
+
+type Refusal = { code: string; example: number }
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === 'object' && value !== null && !Array.isArray(value)
+}
+
+function isCheck(value: unknown): value is Check {
+  return checks.some((check) => check === value)
+}
+
+function isKind(value: unknown): value is ExceptionKind {
+  return value === 'mark-model' || value === 'pending' || value === 'unspellable'
+}
+
+function isSpecExample(value: unknown): value is SpecExample {
+  if (!isRecord(value)) return false
+  return typeof value['example'] === 'number' && typeof value['html'] === 'string' && typeof value['markdown'] === 'string' && typeof value['section'] === 'string'
+}
+
+function isException(value: unknown): value is Exception {
+  if (!isRecord(value)) return false
+  return (
+    isCheck(value['check']) &&
+    typeof value['divergence'] === 'string' &&
+    value['divergence'].length > 0 &&
+    typeof value['example'] === 'number' &&
+    isKind(value['kind']) &&
+    typeof value['reason'] === 'string' &&
+    value['reason'].length > 0
+  )
+}
+
+function isRefusal(value: unknown): value is Refusal {
+  if (!isRecord(value)) return false
+  return typeof value['code'] === 'string' && value['code'].length > 0 && typeof value['example'] === 'number'
+}
+
+function readJson<T>(name: string, guard: (value: unknown) => value is T, shape: string): T[] {
+  const parsed: unknown = JSON.parse(readFileSync(join(root, name), 'utf8'))
+  assert.ok(Array.isArray(parsed), `${name} is not an array`)
+  return parsed.map((value, index) => {
+    assert.ok(guard(value), `${name} holds a ${shape} with the wrong shape at ${index}`)
+    return value
+  })
+}
+
+const spec = readJson('spec.json', isSpecExample, 'spec example')
+const exceptions = readJson('exceptions.json', isException, 'exception')
+const refusals = readJson('refusals.json', isRefusal, 'refusal')
+
+const exampleToRefusal = new Map(refusals.map((refusal) => [refusal.example, refusal.code]))
+const exceptionIndex = new Map(exceptions.map((entry) => [`${entry.example}:${entry.check}`, entry]))
+
+test('the CommonMark spec suite is 0.31.2, vendored byte-exact', () => {
+  const digest = createHash('sha256').update(readFileSync(join(root, 'spec.json'))).digest('hex')
+  assert.equal(digest, 'd431b29d97b6f73e69d547109cf5081578fac931e72afe95639ebe766c1b2a20')
+})
+
+test('every exception is unique, names a parsing example, and files a fixpoint only as unspellable', () => {
+  assert.equal(exceptionIndex.size, exceptions.length, 'one exception repeats an example and check another holds')
+  for (const entry of exceptions) {
+    assert.ok(spec.some((candidate) => candidate.example === entry.example), `exception ${entry.example} names no example in the suite`)
+    assert.equal(exampleToRefusal.get(entry.example), undefined, `exception ${entry.example} is on the refusal list, not an exception`)
+    if (entry.check === 'fixpoint') assert.equal(entry.kind, 'unspellable', `exception ${entry.example} files a fixpoint divergence as ${entry.kind}; a fixable hole is given the spelling instead`)
+  }
+})
+
+test('the refusal list is unique per example and names real examples', () => {
+  assert.equal(exampleToRefusal.size, refusals.length, 'one refusal repeats an example another holds')
+  for (const example of exampleToRefusal.keys()) assert.ok(spec.some((entry) => entry.example === example), `refusal ${example} names no example in the suite`)
+})
+
+// A mark is counted once per text node it touches (AGENTS.md §14).
+const countKeys = ['a', 'blockquote', 'br', 'code', 'em', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'hr', 'img', 'li', 'ol', 'pre', 'strong', 'ul']
+const nodeElement: Record<string, string> = {
+  blockquote: 'blockquote',
+  bulletList: 'ul',
+  codeBlock: 'pre',
+  hardBreak: 'br',
+  listItem: 'li',
+  media: 'img',
+  mediaInline: 'img',
+  orderedList: 'ol',
+  rule: 'hr',
+}
+const markElement: Record<string, string> = { code: 'code', em: 'em', link: 'a', strong: 'strong' }
+const blockTags = new Set(['blockquote', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'hr', 'li', 'ol', 'p', 'pre', 'ul'])
+
+function tagName(tag: string): string {
+  return tag.slice(1).replace(/^\//, '').split(/[\s/>]/)[0] ?? ''
+}
+
+function emptyCounts(): Record<string, number> {
+  return Object.fromEntries(countKeys.map((key) => [key, 0]))
+}
+
+function referenceCounts(html: string): Record<string, number> {
+  const counts = emptyCounts()
+  let inPre = false
+  for (let index = 0; index < html.length; index += 1) {
+    if (html[index] !== '<') continue
+    const close = html.indexOf('>', index)
+    if (close === -1) break
+    const tag = html.slice(index, close + 1)
+    if (tag.startsWith('</')) {
+      if (tagName(tag) === 'pre') inPre = false
+      index = close
+      continue
+    }
+    const name = tagName(tag)
+    if (name === 'pre') {
+      inPre = true
+      counts['pre'] = (counts['pre'] ?? 0) + 1
+    } else if (name === 'code' && inPre) {
+      // A code block's `<code>` is the `<pre>`'s body, already counted.
+    } else if (countKeys.includes(name)) {
+      counts[name] = (counts[name] ?? 0) + 1
+    }
+    index = close
+  }
+  return counts
+}
+
+function nodeCounts(document: AdfNode): Record<string, number> {
+  const counts = emptyCounts()
+  const pending: AdfNode[] = [document]
+  while (pending.length > 0) {
+    const node = pending.pop()
+    if (node === undefined) continue
+    if (node.text !== undefined) {
+      const seen = new Set<string>()
+      for (const mark of node.marks ?? []) {
+        const element = markElement[mark.type]
+        if (element !== undefined) seen.add(element)
+      }
+      for (const element of seen) counts[element] = (counts[element] ?? 0) + 1
+      continue
+    }
+    if (node.type === 'heading') {
+      const level = node.attrs?.['level']
+      if (typeof level === 'number') counts[`h${level}`] = (counts[`h${level}`] ?? 0) + 1
+      pending.push(...(node.content ?? []))
+      continue
+    }
+    const element = nodeElement[node.type]
+    if (element !== undefined) counts[element] = (counts[element] ?? 0) + 1
+    pending.push(...(node.content ?? []))
+  }
+  return counts
+}
+
+const namedEntity: Record<string, string> = { amp: '&', gt: '>', lt: '<', ouml: 'ö', quot: '"' }
+
+function decodeHtmlEntity(text: string, index: number): { length: number; text: string } | undefined {
+  if (text[index] !== '&') return undefined
+  const end = text.indexOf(';', index)
+  if (end === -1 || end - index > 8) return undefined
+  const reference = text.slice(index, end + 1)
+  const named = namedEntity[reference.slice(1, -1)]
+  return named === undefined ? undefined : { length: reference.length, text: named }
+}
+
+test('the oracle decodes every entity the reference HTML holds', () => {
+  for (const example of spec) {
+    for (const [reference] of example.html.matchAll(/&#?[0-9A-Za-z]+;/g)) {
+      assert.ok(decodeHtmlEntity(reference, 0) !== undefined, `example ${example.example} holds ${reference}, which the oracle would leave literal`)
+    }
+  }
+})
+
+function referenceText(html: string): string {
+  const parts: string[] = []
+  let preDepth = 0
+  let atBoundary = true
+  let skipNewline = false
+  for (let index = 0; index < html.length; index += 1) {
+    const character = html.charAt(index)
+    if (character === '<') {
+      const close = html.indexOf('>', index)
+      if (close === -1) break
+      const tag = html.slice(index, close + 1)
+      const name = tagName(tag)
+      if (name === 'br') {
+        parts.push(' ')
+        atBoundary = false
+        skipNewline = true
+        index = close
+        continue
+      }
+      if (name === 'pre') {
+        if (tag.startsWith('</')) {
+          preDepth -= 1
+          trimTrailingNewline(parts)
+        } else {
+          preDepth += 1
+        }
+        atBoundary = true
+      } else {
+        atBoundary = blockTags.has(name)
+      }
+      index = close
+      continue
+    }
+    if (character === '\n') {
+      if (skipNewline) {
+        skipNewline = false
+        continue
+      }
+      if (preDepth > 0) {
+        parts.push('\n')
+        continue
+      }
+      if (!atBoundary && !followedByBlock(html, index + 1)) parts.push(' ')
+      continue
+    }
+    const reference = decodeHtmlEntity(html, index)
+    if (reference !== undefined) {
+      parts.push(reference.text)
+      atBoundary = false
+      index += reference.length - 1
+      continue
+    }
+    parts.push(character)
+    atBoundary = false
+  }
+  return parts.join('')
+}
+
+function trimTrailingNewline(parts: string[]): void {
+  const last = parts[parts.length - 1]
+  if (last === undefined) return
+  parts[parts.length - 1] = last.endsWith('\n') ? last.slice(0, -1) : last
+}
+
+// A newline beside a block open or close is a boundary rather than a soft break, so it spells no space.
+function followedByBlock(html: string, index: number): boolean {
+  let next = index
+  while (next < html.length && (html[next] === '\n' || html[next] === ' ' || html[next] === '\t')) next += 1
+  if (next >= html.length) return true
+  if (html[next] !== '<') return false
+  const close = html.indexOf('>', next)
+  return close !== -1 && blockTags.has(tagName(html.slice(next, close + 1)))
+}
+
+function concatenatedText(document: AdfNode): string {
+  const parts: string[] = []
+  const pending: { inCode: boolean; node: AdfNode }[] = [{ inCode: false, node: document }]
+  while (pending.length > 0) {
+    const frame = pending.pop()
+    if (frame === undefined) continue
+    const { inCode, node } = frame
+    if (node.text !== undefined) {
+      parts.push(inCode ? node.text : node.text.replace(/\n/g, ' '))
+      continue
+    }
+    if (node.type === 'hardBreak') {
+      parts.push(' ')
+      continue
+    }
+    const childInCode = inCode || node.type === 'codeBlock'
+    const content = node.content ?? []
+    for (let index = content.length - 1; index >= 0; index -= 1) {
+      const child = content[index]
+      if (child !== undefined) pending.push({ inCode: childInCode, node: child })
+    }
+  }
+  return parts.join('')
+}
+
+function fixpointRefused(example: SpecExample, document: AdfDocument): string | undefined {
+  const emitted = adfToMarkdown(document)
+  if (!emitted.ok) return emitted.error.code
+  const again = markdownToAdf(emitted.value)
+  assert.ok(again.ok, `example ${example.example} emits markdown it cannot read back`)
+  assert.deepEqual(again.value, document, `example ${example.example} does not hold its own round-trip`)
+  return undefined
+}
+
+function textMismatch(example: SpecExample, document: AdfDocument): string | undefined {
+  const expected = referenceText(example.html)
+  const actual = concatenatedText(document)
+  return expected === actual ? undefined : `${JSON.stringify(expected)} against ${JSON.stringify(actual)}`
+}
+
+function countMismatch(example: SpecExample, document: AdfDocument): string | undefined {
+  const expected = referenceCounts(example.html)
+  const actual = nodeCounts(document)
+  const names = countKeys.filter((key) => expected[key] !== actual[key])
+  return names.length === 0 ? undefined : names.map((name) => `${name} ${expected[name]}/${actual[name]}`).join(' ')
+}
+
+for (const example of spec) {
+  test(`CommonMark example ${example.example} => ${example.section}`, () => {
+    const parse = markdownToAdf(example.markdown)
+    const refused = exampleToRefusal.get(example.example)
+    if (refused !== undefined) {
+      assert.ok(!parse.ok, `example ${example.example} was expected to refuse with ${refused} but parsed`)
+      assert.equal(parse.error.code, refused, `example ${example.example} refused with a different code`)
+      return
+    }
+    if (!parse.ok) assert.fail(`example ${example.example} was expected to parse but refused with ${parse.error.code}`)
+
+    const divergences: Record<Check, string | undefined> = {
+      count: countMismatch(example, parse.value),
+      fixpoint: fixpointRefused(example, parse.value),
+      text: textMismatch(example, parse.value),
+    }
+    for (const check of checks) {
+      const entry = exceptionIndex.get(`${example.example}:${check}`)
+      const divergence = divergences[check]
+      if (divergence === undefined) {
+        assert.equal(entry, undefined, `example ${example.example} passes its ${check} check but files an exception`)
+      } else {
+        assert.ok(entry !== undefined, `example ${example.example} ${check} check fails: ${divergence}`)
+        assert.equal(entry.divergence, divergence, `example ${example.example} ${check} diverged differently than filed`)
+      }
+    }
+  })
+}

src/corpus.test.ts

@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict'
 import { readFileSync, readdirSync } from 'node:fs'
-import { basename, dirname, join } from 'node:path'
+import { basename, dirname, join, sep } from 'node:path'
 import test from 'node:test'
 import { fileURLToPath } from 'node:url'
 
@@ -53,12 +53,13 @@ function pairedNames(root: string, first: string, second: string): string[] {
 function corpusJsonPaths(): string[] {
   return readdirSync(corpusRoot, { encoding: 'utf8', recursive: true })
     .filter((name) => name.endsWith('.json'))
+    .filter((name) => name !== `commonmark-spec${sep}spec.json`)
     .map((name) => join(corpusRoot, name))
     .sort()
 }
 
 test('every corpus directory is a kind the runner reads', () => {
-  assert.deepEqual(directoryNames(corpusRoot), ['errors', 'normalization', 'round-trip'])
+  assert.deepEqual(directoryNames(corpusRoot), ['commonmark-spec', 'errors', 'normalization', 'round-trip'])
 })
 
 test('every round-trip directory is a kind the runner reads', () => {

todo.md

@@ -53,7 +53,7 @@ The numbering is the order the work was planned in, not the order it ships.
   - [x] **3i — The inline nodes and the marks.**
   - [x] **3j — The carry and the combinations.**
   - [ ] **3k — The CommonMark spec suite (`0.2.0`).** Checked in at `corpus/commonmark-spec/`,
-        pinned to the version it ships — the one `html-blocks.ts` names for its start
+        pinned to the version it ships — the one `commonmark-grammar.ts` names for its start
         conditions — `corpus/README.md` gaining the kind.
         **Settled** (the maintainer, 2026-08-27): three checks an example must pass, the reference
         HTML each ships read as corpus data — which adds no format and no direction (§1). §2's
@@ -67,9 +67,11 @@ The numbering is the order the work was planned in, not the order it ships.
         counts close both. The exception list stays the maintainer's, and one entry is owed
         already: 3h continues a list across the marker change CommonMark splits on, so an example
         the reference HTML gives two `<ul>` counts one `bulletList`. One outcome is no
-        exception and must not be filed as one: valid CommonMark parsing to a document
+        exception and must not be filed as one: a fixable §2 hole — valid CommonMark parsing to a
-        `adfToMarkdown` refuses is a §2 hole, which is what `corpus/unspellable/` held until 3c,
+        document `adfToMarkdown` refuses — which is what `corpus/unspellable/` held until 3c, 3e
-        3e and 3h landed their answers and emptied it.
+        and 3h landed their answers and emptied it. The permanent ones — a link destination or
+        title no escape spells, a paragraph opening with a code span — are the exceptions, named
+        by AGENTS.md §2.
 - [ ] **4 — Round-trip property tests (`0.2.0`)**, widening 3j's corpus round-trip past the
       documents a human wrote — the thing that proves 2 and 3 beyond them. Editor-normal (§2) is
       finished here, on 3i's merging — `toEditorNormal(doc)` and the equality the round-trip