fix: preserve inline code capitalization in CLI

src/core.ts

@@ -17,6 +17,34 @@ const isTerm = (word: string, line: string) => {
   });
 };
 
+const indexCodeSpans = (line: string) => {
+  const spans = new Map<number, number>();
+  const nextEnds = new Map<number, number>();
+
+  // Index the nearest closing run of each length without rescanning the suffix.
+  for (let end = line.length; end > 0;) {
+    if (line[end - 1] !== '`') {
+      end--;
+      continue;
+    }
+    let start = end - 1;
+    while (start > 0 && line[start - 1] === '`') {
+      start--;
+    }
+
+    const length = end - start;
+    spans.set(start, nextEnds.get(length) ?? end);
+    // An escaped first backtick leaves the rest of the run as a possible opener.
+    if (length > 1) {
+      spans.set(start + 1, nextEnds.get(length - 1) ?? end);
+    }
+    nextEnds.set(length, end);
+    end = start;
+  }
+
+  return spans;
+};
+
 const lineToWords = (line: string) => {
   const words: WordMeta[] = [];
 
@@ -25,8 +53,18 @@ const lineToWords = (line: string) => {
     value: '',
   };
 
-  for (const char of line.split('')) {
-    if (/\s/.test(char)) {
+  const codeSpans = indexCodeSpans(line);
+
+  for (let index = 0; index < line.length; index++) {
+    let char = line[index];
+    if (char === '\\' && /[\\`]/.test(line[index + 1] ?? '')) {
+      char += line[++index];
+    } else if (char === '`') {
+      const end = codeSpans.get(index)!;
+      char = line.slice(index, end);
+      index = end - 1;
+    }
+    if (/^\s$/.test(char)) {
       if (lastWord.type === 'space') {
         lastWord.value += char;
       } else {

test/index.test.js

@@ -49,6 +49,26 @@ test('should format line as expected', () => {
   );
 });
 
+test('should preserve inline code while formatting heading text', () => {
+  const cases = [
+    ['## Use `Foo Bar Baz` Component', '## Use `Foo Bar Baz` component'],
+    [
+      '## Use ``Foo `Bar` Baz`` Component',
+      '## Use ``Foo `Bar` Baz`` component',
+    ],
+    ['## Use `Foo Bar Component', '## Use `Foo bar component'],
+    [
+      '## Use \\`Foo Bar Baz\\` Component',
+      '## Use \\`Foo bar Baz\\` component',
+    ],
+    ['## Use \\``Foo Bar Baz` Component', '## Use \\``Foo Bar Baz` component'],
+  ];
+
+  for (const [input, expected] of cases) {
+    assert.strictEqual(formatLine(input), expected);
+  }
+});
+
 test('should preserve the existing CLI check and write usage', async () => {
   const cwd = await fs.mkdtemp(path.join(os.tmpdir(), 'heading-case-cli-'));
   const filePath = path.join(cwd, 'guide.md');