Site B: test-website-b.pages.dev
Site B hosts a Cloudflare Pages Function at
/de-amp-download/amp-attachment that serves a valid AMP page
with Content-Disposition: attachment; filename="amp-page.html".
The AMP page contains a canonical link pointing to Site A. With the fix, Brave should download the file instead of De-AMPing to the canonical URL.
Start the test from Site A's test page.