fix(send): keep the root path when REMOVE_TRAILING_SLASH is enabled

The trailing-slash regex also matched the leading slash of the root URL, so with REMOVE_TRAILING_SLASH set every home page view was stored with an empty url_path: the home page vanished from the paths/entry/exit reports and could not be selected as a funnel step. Skip the match at the start of the path so "/" and "/#hash" are preserved while "/blog/" and "/blog/#hash" are still trimmed.

Closes #4152

src/app/api/send/route.test.ts

@@ -482,6 +482,39 @@ describe('event url and referrer parsing', () => {
     expect(saveEventMock.mock.calls[0][0]).toMatchObject({ urlPath: '/blog' });
   });
 
+  test('REMOVE_TRAILING_SLASH keeps the root path as "/"', async () => {
+    process.env.REMOVE_TRAILING_SLASH = '1';
+
+    await callPOST({
+      type: 'event',
+      payload: { website: WEBSITE_ID, hostname: 'example.com', url: '/' },
+    });
+
+    expect(saveEventMock.mock.calls[0][0]).toMatchObject({ urlPath: '/' });
+  });
+
+  test('REMOVE_TRAILING_SLASH keeps the root path when the url has a hash', async () => {
+    process.env.REMOVE_TRAILING_SLASH = '1';
+
+    await callPOST({
+      type: 'event',
+      payload: { website: WEBSITE_ID, hostname: 'example.com', url: '/#hero' },
+    });
+
+    expect(saveEventMock.mock.calls[0][0]).toMatchObject({ urlPath: '/#hero' });
+  });
+
+  test('REMOVE_TRAILING_SLASH strips a trailing slash before the hash', async () => {
+    process.env.REMOVE_TRAILING_SLASH = '1';
+
+    await callPOST({
+      type: 'event',
+      payload: { website: WEBSITE_ID, hostname: 'example.com', url: '/blog/#hero' },
+    });
+
+    expect(saveEventMock.mock.calls[0][0]).toMatchObject({ urlPath: '/blog#hero' });
+  });
+
   test('maps a "/undefined" pathname to an empty url path', async () => {
     await callPOST({
       type: 'event',

src/app/api/send/route.ts

@@ -214,7 +214,8 @@ export async function POST(request: Request) {
       const twclid = currentUrl.searchParams.get('twclid');
 
       if (process.env.REMOVE_TRAILING_SLASH) {
-        urlPath = urlPath.replace(/\/(?=(#.*)?$)/, '');
+        // Never strip the root slash, otherwise the home page is saved with an empty path
+        urlPath = urlPath.replace(/(?!^)\/(?=(#.*)?$)/, '');
       }
 
       if (referrer) {