fix(stringify): render ordered-list start as native numbering (#255)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hendrikheil

packages/comark/SPEC/COMARK/ordered-list-start-wrapper-normalizes.md

@@ -0,0 +1,51 @@
+## Input
+
+```md
+::ol{start="3"}
+1. apple
+2. banana
+::
+```
+
+## AST
+
+```json
+{
+  "frontmatter": {},
+  "meta": {},
+  "nodes": [
+    [
+      "ol",
+      {
+        "start": "3"
+      },
+      [
+        "li",
+        {},
+        "apple"
+      ],
+      [
+        "li",
+        {},
+        "banana"
+      ]
+    ]
+  ]
+}
+```
+
+## HTML
+
+```html
+<ol start="3">
+  <li>apple</li>
+  <li>banana</li>
+</ol>
+```
+
+## Markdown
+
+```md
+3. apple
+4. banana
+```

packages/comark/SPEC/common-mark/ordered-list-start.md

@@ -0,0 +1,57 @@
+## Input
+
+```md
+5. First item
+6. Second item
+7. Third item
+```
+
+## AST
+
+```json
+{
+  "frontmatter": {},
+  "meta": {},
+  "nodes": [
+    [
+      "ol",
+      {
+        "start": "5"
+      },
+      [
+        "li",
+        {},
+        "First item"
+      ],
+      [
+        "li",
+        {},
+        "Second item"
+      ],
+      [
+        "li",
+        {},
+        "Third item"
+      ]
+    ]
+  ]
+}
+```
+
+## HTML
+
+```html
+<ol start="5">
+  <li>First item</li>
+  <li>Second item</li>
+  <li>Third item</li>
+</ol>
+```
+
+## Markdown
+
+```md
+5. First item
+6. Second item
+7. Third item
+```

packages/comark/src/internal/stringify/attributes.ts

@@ -97,6 +97,7 @@ export function resolveAttribute(attrs: Record<string, unknown>, renderData: Nod
 // is implicit in `- [ ]`) so they should not echo back as user attrs.
 const IMPLICIT_ATTRS: Record<string, { drop?: string[]; classBlocklist?: string[] }> = {
   blockquote: { drop: ['as'] },
+  ol: { drop: ['start'] },
   ul: { classBlocklist: ['contains-task-list'] },
   li: { classBlocklist: ['task-list-item'] },
   // `language`/`filename`/`highlights`/`meta` ride on the fence info string.

packages/comark/src/internal/stringify/handlers/ol.ts

@@ -6,7 +6,11 @@ import { comarkAttributes, userBlockAttrs } from '../attributes.ts'
 export async function ol(node: ComarkElement, state: State) {
   const children = node.slice(2) as ComarkNode[]
 
-  const revert = state.applyContext({ list: true, order: 1, listIndent: 3 })
+  // `start` is carried by the native numbering; IMPLICIT_ATTRS drops it from user attrs.
+  const start = Number((node[1] as Record<string, unknown>).start)
+  const order = Number.isInteger(start) && start >= 1 ? start : 1
+
+  const revert = state.applyContext({ list: true, order, listIndent: 3 })
 
   let result = ''
   for (const child of children) {