Add changelog entry

Author: nicohrubec

CHANGELOG.md

@@ -2,6 +2,18 @@
 
 ## Unreleased
 
+### Important Changes
+
+- **feat(tanstackstart-react): Auto-instrument request middleware ([#18989](https://github.com/getsentry/sentry-javascript/pull/18989))**
+
+  The `sentryTanstackStart` Vite plugin now automatically instruments `middleware` arrays in `createFileRoute()`. This captures performance data without requiring manual wrapping with `wrapMiddlewaresWithSentry()`.
+
+- **feat(tanstackstart-react): Auto-instrument server function middleware ([#19001](https://github.com/getsentry/sentry-javascript/pull/19001))**
+
+  The `sentryTanstackStart` Vite plugin now automatically instruments middleware in `createServerFn().middleware([...])` calls. This captures performance data without requiring manual wrapping with `wrapMiddlewaresWithSentry()`.
+
+### Other Changes
+
 - "You miss 100 percent of the chances you don't take. — Wayne Gretzky" — Michael Scott
 
 Work in this release was contributed by @harshit078. Thank you for your contribution!