Add missing-redirects check mention to redirects and configuring-slugs pages

Author: fern-api[bot]

fern/products/docs/pages/seo/configuring-slugs.mdx

@@ -47,6 +47,10 @@ In the example above, the **Welcome** page would be hosted at `plantstore.docs.b
 
 You can customize these default slugs by renaming them or skipping them entirely.
 
+<Note>
+  Changing a slug updates the page's URL. Run [`fern check`](/learn/cli-api-reference/commands#check) to detect pages that moved without a [redirect](/learn/docs/seo/redirects#catching-missing-redirects), so existing links don't break.
+</Note>
+
 ## Renaming slugs
 
 Set the `slug` property in `docs.yml` or in a page's frontmatter to customize the URL path.

fern/products/docs/pages/seo/redirects.mdx

@@ -12,6 +12,22 @@ subtitle: Learn how to configure redirects in Fern Docs. Set up exact path redir
   To add external links to your sidebar navigation, see [Navigation](/learn/docs/configuration/navigation#links).
 </Tip>
 
+## Catching missing redirects
+
+The `missing-redirects` rule for [`fern check`](/learn/cli-api-reference/commands#check) automatically detects pages that were removed or moved without a redirect. It compares your current docs navigation against the previously published state and warns when a previously published URL would return a 404.
+
+The rule defaults to `warn` severity. To treat missing redirects as errors, configure the rule in `docs.yml`:
+
+```yaml docs.yml
+check:
+  rules:
+    missing-redirects: error
+```
+
+The check requires authentication via `fern login` or the `FERN_TOKEN` environment variable. It is skipped on first publish, when unauthenticated, or when the network is unavailable.
+
+For the full list of `fern check` validation rules, see [Check configuration](/learn/docs/configuration/site-level-settings#check-configuration).
+
 <llms-only>
 ## Common errors