From 945b4102f37bcb016fa1e582da0a478f202d0ab1 Mon Sep 17 00:00:00 2001
From: scotttong <scott.tong@gmail.com>
Date: Fri, 7 Aug 2026 18:06:37 -0700
Subject: [PATCH] fix(markdown): respect fenced block closers

---
 packages/shared/src/validators/text.test.ts | 5 +++++
 packages/shared/src/validators/text.ts      | 8 ++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/packages/shared/src/validators/text.test.ts b/packages/shared/src/validators/text.test.ts
index 90950765bd8..cda9ca57a12 100644
--- a/packages/shared/src/validators/text.test.ts
+++ b/packages/shared/src/validators/text.test.ts
@@ -62,6 +62,11 @@ describe("normalizeMidLineHeadings", () => {
     expect(normalizeMidLineHeadings(body)).toBe(body);
   });
 
+  it("does not close a fence marker that has trailing content", () => {
+    const body = "```markdown\n``` still code\ncode ## comment\n```";
+    expect(normalizeMidLineHeadings(body)).toBe(body);
+  });
+
   it("is a no-op when there is no `#` at all", () => {
     const body = "Just some prose with no markers.";
     expect(normalizeMidLineHeadings(body)).toBe(body);
diff --git a/packages/shared/src/validators/text.ts b/packages/shared/src/validators/text.ts
index 1ecf46704bf..62c1b36eba4 100644
--- a/packages/shared/src/validators/text.ts
+++ b/packages/shared/src/validators/text.ts
@@ -7,7 +7,7 @@ export function normalizeEscapedLineBreaks(value: string): string {
     .replace(/\\r/g, "\n");
 }
 
-const FENCE_LINE = /^(\s{0,3})(```+|~~~+)/;
+const FENCE_LINE = /^(\s{0,3})(```+|~~~+)(.*)$/;
 // A mid-line ATX heading marker: 1–6 `#`, a space, then heading text. The
 // capture keeps the char immediately before the run so we can tell a real
 // (collapsed) heading from an inline `#` token like `C#`/`F#`.
@@ -53,7 +53,11 @@ export function normalizeMidLineHeadings(value: string): string {
         inFence = true;
         fenceChar = marker[0]!;
         fenceLength = marker.length;
-      } else if (marker[0] === fenceChar && marker.length >= fenceLength) {
+      } else if (
+        marker[0] === fenceChar
+        && marker.length >= fenceLength
+        && fenceMatch[3]!.trim().length === 0
+      ) {
         inFence = false;
         fenceChar = "";
         fenceLength = 0;