🍿 Minor Changes

• #17174 0224a3a Thanks @matthewp! - Adds the astro preview --background flag to start preview servers as background processes.

  This makes preview servers easier to manage from scripts and AI coding agents because the command returns after the server is ready instead of keeping the terminal attached to the long-running process.

  astro preview --background

  When a preview server is running in the background, you can inspect or stop it with new astro preview subcommands:

  astro preview status
  astro preview logs
  astro preview logs --follow
  astro preview stop

  If Astro detects that astro preview is being run by an AI coding agent, background mode is enabled automatically. This matches the existing behavior for astro dev, allowing agents to continue working after the preview server starts while still receiving the server URL and process ID.

  To opt out of automatic background mode for preview servers, set ASTRO_PREVIEW_BACKGROUND=0 before running astro preview.

• #17532 7f94895 Thanks @florian-lefebvre! - Adds support for paths relative to your project root in logger.entrypoint

  Previously, pointing logger.entrypoint at a custom log handler living in your own project required building an absolute URL. You can now write the path directly:

  import { defineConfig } from 'astro/config';
  
  export default defineConfig({
    logger: {
      entrypoint: new URL('./src/logger.js', import.meta.url),
      entrypoint: './src/logger.js',
    },
  });

  Paths starting with ./ or ../ are resolved against your project root. Package specifiers such as @org/astro-logger, absolute paths, and URL entrypoints keep working as before.

• #17084 961bbe5 Thanks @matthewp! - Widens the AstroPrerenderer render() return type so prerenderers can report incremental-build metadata

  A prerenderer’s render() may now resolve to either a Response (as before) or a PrerenderResult object that pairs the response with the content entries and optimized-image transforms the page resolved. This lets prerenderers that render out of process (for example, in an adapter’s runtime like workerd) report those dependencies back to the build, so incremental static builds can track and replay them for skipped pages.

  import type { AstroPrerenderer, PrerenderResult } from 'astro';
  
  const prerenderer: AstroPrerenderer = {
    name: 'my-adapter:prerenderer',
    getStaticPaths,
    async render(request, { routeData }): Promise<PrerenderResult> {
      const { response, metadata } = await renderInRuntime(request, routeData);
      return { response, metadata };
    },
  };

  This is a non-breaking widening: prerenderers that return a bare Response continue to work unchanged, and in-process prerenderers can keep returning a Response since the build collects their metadata directly.

• #16871 90c98ae Thanks @adamchal! - Adds session: false in astro.config to opt out of session support. Projects that do not set session: false see no behavior change.

  import { defineConfig } from 'astro/config';
  
  export default defineConfig({
    session: false,
  });

  The session runtime and dependencies (unstorage) are now tree-shaken out of the SSR bundle for any project where no session driver is wired via:

  • session: false
  • no session config at all
  • a session config without a driver

  Useful for serverless/edge runtimes where cold-start parse time is sensitive.

• #17084 961bbe5 Thanks @matthewp! - Adds experimental support for incremental static builds with experimental.incrementalBuild.

  When enabled, Astro can skip regenerating static pages from dynamic routes when both the page’s module dependencies and its data cache key are unchanged from the previous build. This currently applies to pages returned from getStaticPaths() that include a cacheKey.

  import { defineConfig } from 'astro/config';
  
  export default defineConfig({
    experimental: {
      incrementalBuild: true,
    },
  });

  Return a cacheKey for each generated page from getStaticPaths():

  ---
  export async function getStaticPaths() {
    const posts = await fetchPosts();
  
    return posts.map((post) => ({
      params: { slug: post.slug },
      props: { post },
      cacheKey: post.digest,
    }));
  }
  ---

  For incremental builds to skip rendering in CI, Astro’s cache directory must be preserved between builds. Astro empties the output directory on each build and restores skipped pages from the cache directory, so only that directory needs to persist. For the default config, cache and restore node_modules/.astro/ before running astro build.

  See the experimental incremental static builds documentation for more information.

• #17084 961bbe5 Thanks @matthewp! - Adds the optional digest property to content collection entries.

  Loaders can provide an opaque digest value that changes when an entry changes. This is now reflected in the CollectionEntry type returned by getCollection() and getEntry(), making it easier to detect content changes without re-hashing large entry bodies.

  ---
  import { getCollection } from 'astro:content';
  
  const posts = await getCollection('blog');
  
  for (const post of posts) {
    console.log(post.digest);
  }
  ---

  The property is optional because not every loader provides a digest. See incremental static builds for how digest can be used as a cacheKey.

🐞 Patch Changes

• #17534 5a5337e Thanks @florian-lefebvre! - Improves logger.entrypoint reference docs

• #17529 d52a787 Thanks @QVinto! - Fixes astro dev crashing with Invalid URL when --host is set to a specific non-loopback address

  Vite only reports a local URL for loopback hosts. When the dev server was started with --host <custom-address> bound to a specific non-loopback address (a LAN or Tailscale IP, for example), the URL was reported under network and local was empty, so writing the dev lock file threw Invalid URL and killed a server that had already started successfully.

  The lock file URL now falls back to the network URL, and a server that exposes no URL at all is left untracked rather than being taken down by lock file bookkeeping.

• #17566 296248c Thanks @astrobot-houston! - Fixes fontProviders.googleicons() returning the full icon font (~3.9MB) instead of only the requested glyphs when multiple experimental.glyphs are specified

• #17560 ef45de1 Thanks @astrobot-houston! - Fixes Astro.url.pathname for non-index pages when using build.format: 'preserve'. Previously, a page like src/pages/about-me.astro would output to dist/about-me.html but Astro.url.pathname would incorrectly return /about-me/ instead of /about-me.html.

• #17573 0089f83 Thanks @astrobot-houston! - Fixes a Content Layer build crash that could occur when another dependency causes an older version of neotraverse to be hoisted to the project root

• #17571 116f700 Thanks @astrobot-houston! - Fixes cookies set via Astro.cookies.set() inside a custom 404.astro or 500.astro error page being silently dropped from the final response

• #17579 3ea55ce Thanks @bluwy! - Supports the devEngines field in package.json when detecting the package manager for install commands

• #17422 e4e2037 Thanks @jiwonyoon-dev! - Fixes popover being rendered as popover="true"/popover="false" on custom elements (tag names containing a hyphen). Per the Popover API, the attribute only accepts "auto", "manual", or being absent, so boolean values are now always rendered as a bare popover attribute (or omitted), regardless of the tag name.