Fix cell/outline breakage after single-line display math with attributes

packages/core/src/markdownit/math.ts

@@ -163,13 +163,15 @@ function math_block(
   if (silent) {
     return true;
   }
-  if (firstLine.trim().slice(-2) === "$$") {
-    // Single line expression
-    firstLine = firstLine.trim().slice(0, -2);
+  let attrStr = undefined;
+  const singleLineMatch = firstLine.trim().match(/^(.*)\$\$\s*(\{.*\})?\s*$/);
+  if (singleLineMatch) {
+    // Single line expression, optionally followed by attributes (e.g. {#eq-label})
+    firstLine = singleLineMatch[1];
+    attrStr = singleLineMatch[2];
     found = true;
   }
 
-  let attrStr = undefined;
   for (next = start; !found; ) {
     next++;
 

packages/core/test/markdownit-math.test.ts

@@ -0,0 +1,42 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import MarkdownIt from "markdown-it";
+import { mathjaxPlugin } from "../src/markdownit/math";
+
+const parse = (src: string) => {
+  const md = new MarkdownIt({ html: true });
+  md.use(mathjaxPlugin);
+  return md.parse(src, {});
+};
+
+test("single-line math with attributes does not swallow the rest of the document", () => {
+  const tokens = parse(
+    "$$1+1$$ {#eq-spec0}\n\n```{python}\n2+2\n```\n"
+  );
+  const math = tokens.filter((t) => t.type === "math_block");
+  const fences = tokens.filter((t) => t.type === "fence");
+  assert.equal(math.length, 1);
+  assert.equal(math[0].info, "{#eq-spec0}");
+  assert.equal(math[0].content.trim(), "1+1");
+  assert.equal(fences.length, 1);
+});
+
+test("single-line math without attributes still parses", () => {
+  const tokens = parse("$$1+1$$\n\n```{python}\n2+2\n```\n");
+  const math = tokens.filter((t) => t.type === "math_block");
+  const fences = tokens.filter((t) => t.type === "fence");
+  assert.equal(math.length, 1);
+  assert.equal(math[0].content.trim(), "1+1");
+  assert.equal(fences.length, 1);
+});
+
+test("multi-line math with attributes on the closing line still parses", () => {
+  const tokens = parse("$$\n1+1\n$$ {#eq-spec0}\n\n```{python}\n2+2\n```\n");
+  const math = tokens.filter((t) => t.type === "math_block");
+  const fences = tokens.filter((t) => t.type === "fence");
+  assert.equal(math.length, 1);
+  assert.equal(math[0].info, "{#eq-spec0}");
+  assert.equal(math[0].content.trim(), "1+1");
+  assert.equal(fences.length, 1);
+});