Cloudflare Bundler Apps

This skill teaches how to build apps that deploy cleanly through the space deploy pipeline. Every project committed to a space is built by @cloudflare/worker-bundler (createApp when there are static assets, createWorker when there are none) and served on a Dynamic Worker via WorkerLoader. Get the conventions right and the preview "just works". Get them wrong and you get a blank page, a 500, or a Build failed error.

How the pipeline works

When deploy_space(branch) is called, the space DO:

1. Reads every file from the branch's working tree (skipping .git/).
2. Parses wrangler.json / wrangler.jsonc / wrangler.toml for main, compatibility_date, compatibility_flags, and [assets].
3. If [assets].directory is set, files under that directory become static assets served host-side by handleAssetRequest. Everything else is built into a Worker via createApp (with server: <main>).
4. If no assets directory is configured, only createWorker({ entryPoint: <main> }) is run. The output is loaded as a Dynamic Worker; all requests go to the Worker.
5. Previews are served at /space/:name/preview/:branch/*. Responses with content-type: text/html are run through HTMLRewriter, which prefixes root-relative src / href / action attributes with the preview base path. JS-side fetches and dynamic imports are NOT rewritten.

Practical consequences:

• You can rely on root-relative src="/foo.js" and href="/style.css" in HTML. They will be rewritten to the preview path automatically.
• You cannot rely on root-relative paths inside JS strings: fetch("/api/x"), new URL("/foo", location.origin), dynamic import("/lib.js"). These hit the wrong path under the preview prefix. Use relative paths (./api/x, import.meta.url) or read the base path from <base href> / a meta tag injected at build time.
• The <base href> tag is also rewritten if present, using it lets all relative URLs resolve against the preview path.