[v6] deprecate Astro in getStaticPaths

src/content/docs/en/guides/upgrade-to/v6.mdx

@@ -97,6 +97,32 @@ The following deprecated features are no longer supported and are no longer docu
 
 Some deprecated features may temporarily continue to function until they are completely removed. Others may silently have no effect, or throw an error prompting you to update your code.
 
+### `Astro` in `getStaticPaths()`
+
+<SourcePR number="14432" title="feat: deprecate Astro in getStaticPaths"/>
+
+In Astro 5.x, it was possible to access an `Astro` object inside `getStaticPaths()`. However, despite being typed the same as the `Astro` object accessible in the frontmatter, this object only had `site` and `generator` properties. This could lead to confusion about which `Astro` object properties were available inside `getStaticPaths()`.
+
+Astro 6.0 deprecates this object for `getStaticPaths()` to avoid confusion and improves error handling when attempting to access `Astro` values that are unavailable. Using `Astro.site` or `Astro.generator` within `getStaticPaths()` will now log a deprecation warning, and accessing any other property will throw a specific error with a helpful message. In a future major version, this object will be removed entirely, and accessing `Astro.site` or `Astro.generator` will also throw an error.
+
+#### What should I do?
+
+Update your `getStaticPaths()` function if you were attempting to access any `Astro` properties inside its scope. Remove `Astro.generator` entirely, and replace all occurrences of `Astro.site()` with `import.meta.env.SITE`:
+
+```astro title="src/pages/blog/[slug].astro" del={5,6} ins={7}
+---
+import { getPages } from "../../../utils/data";
+
+export async function getStaticPaths() {
+  console.log(Astro.generator);
+  return getPages(Astro.site);
+  return getPages(import.meta.env.SITE);
+}
+---
+```
+
+<ReadMore>Read more about [built-in environment variables such as `import.meta.env.SITE`](/en/guides/environment-variables/#default-environment-variables) that are accessible when [using `getStaticPaths()` to dynamically generate static routes](/en/guides/routing/#static-ssg-mode).</ReadMore>
+
 ## Removed
 
 The following features have now been entirely removed from the code base and can no longer be used. Some of these features may have continued to work in your project even after deprecation. Others may have silently had no effect.