docs(nextjs): document the route manifest injection option (#16076)

This document outlines the new option introduced in
getsentry/sentry-javascript#18798, which was
released in `10.34.0`.

This option replaces the `disableManifestinjection` option, providing
users with the flexibility to either completely disable this behavior or
selectively exclude specific routes from being included in the route
manifest.

A common use case for this option is when some routes are private or
contain unreleased features. Having these routes present in the route
manifest posed challenges for certain users. To address this, an
`exclude` option allows users to avoid the all-or-nothing compromise,
ensuring that data quality is maintained and preventing the leakage of
route information.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Sarah Mischinger <sarah@codingwriter.com>

Author: 3 people

docs/platforms/javascript/guides/nextjs/configuration/build/index.mdx

@@ -222,18 +222,52 @@ Enables the use of the [`runAfterProductionCompile` hook from Next.js](https://n
 
 </SdkOption>
 
-<SdkOption name="disableManifestInjection" type="boolean|undefined" defaultValue="false">
+<SdkOption name="routeManifestInjection" type="boolean|object" defaultValue="true">
 
-Disables automatic injection of the route manifest into the client bundle.
+<AvailableSince version="10.34.0" />
 
-The route manifest is a build-time generated mapping of your Next.js App Router routes that enables Sentry to group transactions by parameterized route names (e.g., `/users/:id` instead of `/users/123`, `/users/456`, etc.).
+<Alert level="info" title="App Router only">
+  `routeManifestInjection` option is only supported in the App Router.
+</Alert>
+
+Controls injection and filtering of the route manifest in the client bundle.
+
+The route manifest is a build-time generated mapping of your Next.js App Router routes that enables Sentry to group transactions by parameterized route names (for example, `/users/:id` instead of `/users/123` or `/users/456`).
+
+You can set this option to `false` to disable the route manifest injection.
 
 **Disable this option if:**
 
 - You want to minimize client bundle size
 - You're experiencing build issues related to route scanning
 - You prefer raw URLs in transaction names
-- You're only using the Pages Router (this feature is only supported in the App Router)
+
+You can also pass in an object with an `exclude` property to control which routes should be excluded from the route manifest. The `exclude` property accepts an array of strings or regular expressions, or a function that returns `true` to exclude a route.
+
+```javascript
+withSentryConfig(nextConfig, {
+  // Exclude specific routes using an array of strings or RegExps
+  routeManifestInjection: {
+    exclude: ["/api/health", "/api/excluded/[parameter]", /^\/internal\//],
+  },
+});
+```
+
+```javascript
+withSentryConfig(nextConfig, {
+  // Or use a function for dynamic exclusion
+  routeManifestInjection: {
+    exclude: (route) => route.includes("/excluded"),
+  },
+});
+```
+
+Excluded routes will appear as raw URLs in transaction names instead of parameterized routes.
+
+**Use `exclude` if:**
+
+- You want to hide internal or unreleased routes from appearing in the client bundle
+- You want to reduce bundle size by excluding routes that don't benefit from parameterized grouping (for example, static routes with no dynamic segments)
 
 </SdkOption>