From 377a77de605831472e6f6381e36233546ea88a67 Mon Sep 17 00:00:00 2001
From: Punyapal Shah <53343069+MrPunyapal@users.noreply.github.com>
Date: Wed, 4 Nov 2026 02:37:52 +0530
Subject: [PATCH 1/2] fix: keep formatting out of unselected lines

---
 resources/js/lib/markdown-format.ts |  4 +++-
 tests/Unit/MarkdownFormat.test.ts   | 11 +++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/resources/js/lib/markdown-format.ts b/resources/js/lib/markdown-format.ts
index b193d03df..c0d3e7f84 100644
--- a/resources/js/lib/markdown-format.ts
+++ b/resources/js/lib/markdown-format.ts
@@ -73,7 +73,9 @@ export function formatMarkdown(
 
     const prefix = PREFIXES[format] ?? (() => '');
     const from = value.lastIndexOf('\n', start - 1) + 1;
-    const lineEnd = value.indexOf('\n', end);
+    // A selection ending just after a newline does not include the next line.
+    const lastSelected = end > start && value[end - 1] === '\n' ? end - 1 : end;
+    const lineEnd = value.indexOf('\n', lastSelected);
     const to = lineEnd === -1 ? value.length : lineEnd;
     const insert = value
         .slice(from, to)
diff --git a/tests/Unit/MarkdownFormat.test.ts b/tests/Unit/MarkdownFormat.test.ts
index b6e0fb6bf..93454bb80 100644
--- a/tests/Unit/MarkdownFormat.test.ts
+++ b/tests/Unit/MarkdownFormat.test.ts
@@ -35,3 +35,14 @@ await test('prefixes every line the selection touches', () => {
     assert.deepEqual(apply('What shipped', 3, 3, 'heading'), ['## What shipped', '']);
     assert.deepEqual(apply('a\nquote', 2, 2, 'quote'), ['a\n> quote', '']);
 });
+
+await test('does not prefix the next line when selection ends after a newline', () => {
+    assert.deepEqual(apply('first\nsecond', 0, 6, 'bulleted'), [
+        '- first\nsecond',
+        '',
+    ]);
+    assert.deepEqual(apply('first\nsecond\nthird', 0, 13, 'numbered'), [
+        '1. first\n2. second\nthird',
+        '',
+    ]);
+});

From 59c9b10165009caa0ff8bdcfba5d6787dc7ff3bb Mon Sep 17 00:00:00 2001
From: Punyapal Shah <53343069+MrPunyapal@users.noreply.github.com>
Date: Wed, 4 Nov 2026 02:37:56 +0530
Subject: [PATCH 2/2] fix: handle selected first-line newline in markdown
 formatting

---
 resources/js/lib/markdown-format.ts | 2 +-
 tests/Unit/MarkdownFormat.test.ts   | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/resources/js/lib/markdown-format.ts b/resources/js/lib/markdown-format.ts
index c0d3e7f84..fb7bfa962 100644
--- a/resources/js/lib/markdown-format.ts
+++ b/resources/js/lib/markdown-format.ts
@@ -72,7 +72,7 @@ export function formatMarkdown(
     }
 
     const prefix = PREFIXES[format] ?? (() => '');
-    const from = value.lastIndexOf('\n', start - 1) + 1;
+    const from = start === 0 ? 0 : value.lastIndexOf('\n', start - 1) + 1;
     // A selection ending just after a newline does not include the next line.
     const lastSelected = end > start && value[end - 1] === '\n' ? end - 1 : end;
     const lineEnd = value.indexOf('\n', lastSelected);
diff --git a/tests/Unit/MarkdownFormat.test.ts b/tests/Unit/MarkdownFormat.test.ts
index 93454bb80..77e3cbffb 100644
--- a/tests/Unit/MarkdownFormat.test.ts
+++ b/tests/Unit/MarkdownFormat.test.ts
@@ -46,3 +46,10 @@ await test('does not prefix the next line when selection ends after a newline',
         '',
     ]);
 });
+
+void test('formats a selected first-line newline without an invalid range', () => {
+    assert.deepEqual(apply('\nsecond', 0, 1, 'bulleted'), [
+        '- \nsecond',
+        '',
+    ]);
+});