diff --git a/news/changelog-1.10.md b/news/changelog-1.10.md
index 5d5917be61a..12e87e17433 100644
--- a/news/changelog-1.10.md
+++ b/news/changelog-1.10.md
@@ -104,6 +104,7 @@ All changes included in 1.10:
 - ([#14472](https://github.com/quarto-dev/quarto-cli/issues/14472)): Add support for Kotlin in code annotations and YAML cell options. (author: @barendgehrels)
 - ([#14529](https://github.com/quarto-dev/quarto-cli/issues/14529)): Fix bundled Julia engine path leaking into rendered YAML metadata and pandoc log output when running an installed Quarto. The internal subtree-engine filter only matched the source-tree share-path layout (`resources/extension-subtrees/`) and missed installed layouts where the path is `share/extension-subtrees/`.
 - ([#14576](https://github.com/quarto-dev/quarto-cli/issues/14576)): Fix website render hanging when sidebar titles contain double-underscore (dunder) names.
+- ([#14577](https://github.com/quarto-dev/quarto-cli/issues/14577)): Fix an embedded notebook with no explicit title using a heading that isn't its first content (such as a code-cell comment) as the notebook title. A heading is now only used as the title when nothing precedes it; otherwise the title falls back to the notebook filename.
 - ([#14582](https://github.com/quarto-dev/quarto-cli/issues/14582)): Fix format detection for extension formats (e.g. `acm-pdf`) in project preview, manuscript notebooks, MECA bundles, and website format ordering.
 - ([#14583](https://github.com/quarto-dev/quarto-cli/issues/14583)): Fix a shortcode used as an image source (e.g. `![]({{< meta logo >}})`) getting the `default-image-extension` appended, producing a doubled extension once the shortcode resolves.
 - ([#14595](https://github.com/quarto-dev/quarto-cli/issues/14595)): Fix reload preview in code-server environment
diff --git a/src/core/jupyter/jupyter-embed.ts b/src/core/jupyter/jupyter-embed.ts
index 718c2f03105..8d97b7efd72 100644
--- a/src/core/jupyter/jupyter-embed.ts
+++ b/src/core/jupyter/jupyter-embed.ts
@@ -654,7 +654,18 @@ function findTitle(cells: JupyterCellOutput[]) {
     const partitioned = partitionMarkdown(cell.markdown);
     if (partitioned.yaml?.title) {
       return partitioned.yaml.title as string;
-    } else if (partitioned.headingText) {
+    } else if (partitioned.headingText && !partitioned.contentBeforeHeading) {
+      // Only promote a heading to the title when nothing precedes it. This
+      // borrows the same content-before-heading gate that fixupFrontMatter uses
+      // in jupyter-fixups.ts; the two are not otherwise equivalent (this scans
+      // every cell, fixupFrontMatter inspects only the first markdown cell, and
+      // it can filter on cell.cell_type === "markdown" where findTitle can't —
+      // rendered JupyterCellOutput carries no cell_type).
+      //
+      // The gate is what fixes issue 14577: a code cell's `markdown` is its
+      // fenced source, whose opening fence delimiter always counts as content
+      // before any `#` line inside it, so a code comment can never be mistaken
+      // for the leading heading.
       return partitioned.headingText;
     }
   }
diff --git a/src/core/pandoc/pandoc-partition.ts b/src/core/pandoc/pandoc-partition.ts
index 08cbdf86572..0749ceddf54 100644
--- a/src/core/pandoc/pandoc-partition.ts
+++ b/src/core/pandoc/pandoc-partition.ts
@@ -53,9 +53,10 @@ export function partitionMarkdown(markdown: string): PartitionedMarkdown {
   markdown = partitioned ? partitioned.markdown : markdown;
 
   // extract heading
-  const { lines, headingText, headingAttr } = markdownWithExtractedHeading(
-    markdown,
-  );
+  const { lines, headingText, headingAttr, contentBeforeHeading } =
+    markdownWithExtractedHeading(
+      markdown,
+    );
 
   // does this contain refs?
   const containsRefs = lines.some((line) =>
@@ -66,6 +67,7 @@ export function partitionMarkdown(markdown: string): PartitionedMarkdown {
     yaml: (partitioned ? readYamlFromMarkdown(partitioned.yaml) : undefined),
     headingText,
     headingAttr,
+    contentBeforeHeading,
     containsRefs,
     markdown: lines.join("\n"),
     srcMarkdownNoYaml: partitioned?.markdown || "",
diff --git a/src/core/pandoc/types.ts b/src/core/pandoc/types.ts
index 9a298fa9ea8..33adfeaac52 100644
--- a/src/core/pandoc/types.ts
+++ b/src/core/pandoc/types.ts
@@ -17,6 +17,7 @@ export interface PartitionedMarkdown {
   yaml?: Metadata;
   headingText?: string;
   headingAttr?: PandocAttr;
+  contentBeforeHeading?: boolean;
   containsRefs: boolean;
   markdown: string;
   srcMarkdownNoYaml: string;
diff --git a/tests/docs/smoke-all/2026/06/30/14577.qmd b/tests/docs/smoke-all/2026/06/30/14577.qmd
new file mode 100644
index 00000000000..38a7e5b022f
--- /dev/null
+++ b/tests/docs/smoke-all/2026/06/30/14577.qmd
@@ -0,0 +1,29 @@
+---
+title: "Embed code-comment title (issue 14577)"
+format: html
+_quarto:
+  tests:
+    html:
+      ensureFileRegexMatches:
+        -
+          # The notebook source link uses the filename as the title
+          - 'Source:\s*notebook\.ipynb'
+        -
+          # The Python comment must never be used as the notebook title
+          - 'Source:\s*(#\s*)?plt\.savefig'
+      postRenderCleanup:
+        - notebook-preview.html
+        - notebook.out.ipynb
+        - notebook_files
+---
+
+The embedded notebook has no markdown heading cells and a code cell whose last
+line is a Python comment (`# plt.savefig(...)`). The notebook markdown a code
+cell carries is its fenced source, and heading extraction is not fence-aware,
+so the `#` comment matched the ATX-heading regex and was promoted to the
+notebook title — surfacing in the "Source" link and sidebar.
+
+The title used for the "Source" link must fall back to the notebook filename,
+not the code comment.
+
+{{< embed notebook.ipynb echo=true >}}
diff --git a/tests/docs/smoke-all/2026/06/30/embed-heading-after-content.qmd b/tests/docs/smoke-all/2026/06/30/embed-heading-after-content.qmd
new file mode 100644
index 00000000000..3c20642c4b1
--- /dev/null
+++ b/tests/docs/smoke-all/2026/06/30/embed-heading-after-content.qmd
@@ -0,0 +1,31 @@
+---
+title: "Embedded notebook title aligns with fixupFrontMatter"
+format: html
+_quarto:
+  tests:
+    html:
+      ensureFileRegexMatches:
+        -
+          # No leading heading, so the Source link falls back to the filename
+          - 'Source:\s*heading-after-content\.ipynb'
+        -
+          # A heading with content before it must not become the title
+          - 'Source:\s*Some Header'
+      postRenderCleanup:
+        - heading-after-content-preview.html
+        - heading-after-content.out.ipynb
+        - heading-after-content_files
+---
+
+The embedded notebook's first markdown cell has prose before its only heading
+(`# Some Header`). The heading must not be promoted to the embedded notebook's
+title.
+
+This intentionally aligns the embed title with how a notebook's own
+front-matter title is derived. Since #5363 / #6411 (commit 24672a4af),
+`fixupFrontMatter` only promotes a heading to the notebook title when no
+content precedes it; otherwise no title is set. The embed "Source" link follows
+the same rule and falls back to the filename here, rather than using a heading
+that isn't really the document title.
+
+{{< embed heading-after-content.ipynb >}}
diff --git a/tests/docs/smoke-all/2026/06/30/heading-after-content.ipynb b/tests/docs/smoke-all/2026/06/30/heading-after-content.ipynb
new file mode 100644
index 00000000000..7efb9ec2bc1
--- /dev/null
+++ b/tests/docs/smoke-all/2026/06/30/heading-after-content.ipynb
@@ -0,0 +1,20 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "m1",
+   "metadata": {},
+   "source": ["Some intro content here.\n", "\n", "# Some Header\n", "\n", "More content after the header.\n"]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "c1",
+   "metadata": {},
+   "outputs": [{"name": "stdout", "output_type": "stream", "text": ["hi\n"]}],
+   "source": ["print('hi')"]
+  }
+ ],
+ "metadata": {"kernelspec": {"display_name": "Python 3", "language": "python", "name": "python3"}, "language_info": {"name": "python"}},
+ "nbformat": 4, "nbformat_minor": 5
+}
diff --git a/tests/docs/smoke-all/2026/06/30/notebook.ipynb b/tests/docs/smoke-all/2026/06/30/notebook.ipynb
new file mode 100644
index 00000000000..776d3c30c5f
--- /dev/null
+++ b/tests/docs/smoke-all/2026/06/30/notebook.ipynb
@@ -0,0 +1,35 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "c1",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "hello\n"
+     ]
+    }
+   ],
+   "source": [
+    "print('hello')\n",
+    "# plt.savefig('./fig/Shockley-parity/lowest_solution.svg')"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "name": "python"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}
diff --git a/tests/smoke/embed/render-embed.test.ts b/tests/smoke/embed/render-embed.test.ts
index dfa151177ea..db80d860e6b 100644
--- a/tests/smoke/embed/render-embed.test.ts
+++ b/tests/smoke/embed/render-embed.test.ts
@@ -5,6 +5,7 @@
 *
 */
 import { dirname, extname, join } from "../../../src/deno_ral/path.ts";
+import { safeRemoveSync } from "../../../src/deno_ral/fs.ts";
 import { docs, outputForInput } from "../../utils.ts";
 import {
   ensureFileRegexMatches,
@@ -42,8 +43,8 @@ testRender(input, format, false, [
 ], {
   teardown: () => {
     // clean up the notebook that is referenced by `embed-qmd-qmd`
-    Deno.removeSync(nbOutput);
-    Deno.removeSync(nbSupporting, { recursive: true });
+    safeRemoveSync(nbOutput);
+    safeRemoveSync(nbSupporting, { recursive: true });
 
     return Promise.resolve();
   },
@@ -95,9 +96,9 @@ testRender(ipynbInput, format, false, [
 ], {
   teardown: () => {
     // clean up the notebook that is referenced by `embed-qmd-qmd`
-    Deno.removeSync(ipynbPreviewNb);
-    Deno.removeSync(ipynbPreviewSupporting, { recursive: true });
-    Deno.removeSync(ipynbPreviewRendered);
+    safeRemoveSync(ipynbPreviewNb);
+    safeRemoveSync(ipynbPreviewSupporting, { recursive: true });
+    safeRemoveSync(ipynbPreviewRendered);
 
     return Promise.resolve();
   },
@@ -128,7 +129,7 @@ testRender(docInput, "html", false, [
 
     const cleanup = ["notebook.embed_files", "notebook.embed-preview.html", "notebook2.embed_files", "notebook2.embed-preview.html"];
     cleanup.forEach((path) => {
-      Deno.removeSync(join(dir, path), {recursive: true});
+      safeRemoveSync(join(dir, path), {recursive: true});
     })
     return Promise.resolve();
   },
diff --git a/tests/smoke/smoke-all.test.ts b/tests/smoke/smoke-all.test.ts
index 65b4b08f5f3..1172d2f13e4 100644
--- a/tests/smoke/smoke-all.test.ts
+++ b/tests/smoke/smoke-all.test.ts
@@ -170,7 +170,9 @@ const postRenderCleanup = () => {
   for (const file of postRenderCleanupFiles) {
     console.log(`Cleaning up ${file} in ${Deno.cwd()}`);
     if (safeExistsSync(file)) {
-      Deno.removeSync(file);
+      // recursive so a registered entry can be a directory (e.g. an embedded
+      // notebook's `*_files` support dir), not just a single file
+      safeRemoveSync(file, { recursive: true });
     }
   }
 }