#12441 b4fec3c Thanks @ascorbic! - Adds experimental session support

Sessions are used to store user state between requests for server-rendered pages, such as login status, shopping cart contents, or other user-specific data.
```
---
export const prerender = false; // Not needed in 'server' mode
const cart = await Astro.session.get('cart');
---

<a href="/checkout">🛒 {cart?.length ?? 0} items</a>
```
Sessions are available in on-demand rendered/SSR pages, API endpoints, actions and middleware. To enable session support, you must configure a storage driver.

If you are using the Node.js adapter, you can use the fs driver to store session data on the filesystem:
```
// astro.config.mjs
{
  adapter: node({ mode: 'standalone' }),
  experimental: {
    session: {
      // Required: the name of the unstorage driver
      driver: "fs",
    },
  },
}
```
If you are deploying to a serverless environment, you can use drivers such as redis, netlify-blobs, vercel-kv, or cloudflare-kv-binding and optionally pass additional configuration options.

For more information, including using the session API with other adapters and a full list of supported drivers, see the docs for experimental session support. For even more details, and to leave feedback and participate in the development of this feature, the Sessions RFC.
#12426 3dc02c5 Thanks @oliverlynch! - Improves asset caching of remote images

Astro will now store entity tags and the Last-Modified date for cached remote images and use them to revalidate the cache when it goes stale.
#12721 c9d5110 Thanks @florian-lefebvre! - Adds a new getActionPath() helper available from astro:actions

Astro 5.1 introduces a new helper function, getActionPath() to give you more flexibility when calling your action.

Calling getActionPath() with your action returns its URL path so you can make a fetch() request with custom headers, or use your action with an API such as navigator.sendBeacon(). Then, you can handle the custom-formatted returned data as needed, just as if you had called an action directly.

This example shows how to call a defined like action passing the Authorization header and the keepalive option:
```
<script>
  // src/components/my-component.astro
  import { actions, getActionPath } from 'astro:actions';

  await fetch(getActionPath(actions.like), {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: 'Bearer YOUR_TOKEN',
    },
    body: JSON.stringify({ id: 'YOUR_ID' }),
    keepalive: true,
  });
</script>
```
This example shows how to call the same like action using the sendBeacon API:
```
<script>
  // src/components/my-component.astro
  import { actions, getActionPath } from 'astro:actions';

  navigator.sendBeacon(
    getActionPath(actions.like),
    new Blob([JSON.stringify({ id: 'YOUR_ID' })], {
      type: 'application/json',
    }),
  );
</script>
```

Patch Changes

#12786 e56af4a Thanks @ematipico! - Fixes an issue where Astro i18n didn't properly show the 404 page when using fallback and the option prefixDefaultLocale set to true.
#12758 483da89 Thanks @delucis! - Adds types for ?url&inline and ?url&no-inline import queries added in Vite 6
#12763 8da2318 Thanks @rbsummers! - Fixed changes to vite configuration made in the astro:build:setup integration hook having no effect when target is "client"
#12767 36c1e06 Thanks @ascorbic! - Clears the content layer cache when the Astro config is changed