The search for "fetch-url-file-3A-2F-2F-2F" likely refers to a URL-encoded string ( ), which decodes to fetch?url=file:///

is a forward slash) rather than a standard web address. Usually, strings like fetch-url-file:///

That gives:
file:///

Check Encoding: Ensure your application is not double-encoding the colons and slashes, which can lead to "Bad URI" errors.

part), these resources are essential for understanding the mechanics: URL Encoding & Percent-Encoding: For a "paper" or authoritative guide on why characters like , refer to the MDN Web Docs on encodeURIComponent or the official (the standard for Uniform Resource Identifiers). The Fetch API:

c) Serve files via a local HTTP server

Instead of file:///, use http://localhost:8000 and fetch() normally.
Example with Python: