Fix the locale resolver in a Cloudflare Worker

Your Cloudflare Worker renders a greeting in each visitor's language. The first version stored the detected locale on a shared module object and then awaited a load. Other requests overwrote it in between, so some pages rendered in the wrong language. The fix resolves each request's locale from that request's own Accept-Language header.

An assistant wrote render_locales(accept_language_headers, supported), which resolves a batch of requests. It is in the editor. It has a bug. Find it and fix it.

Input and output:

• accept_language_headers: one Accept-Language header per request, in order. A header can be empty or junk.
• supported: the locales the site supports, in lowercase.
• Return one locale per request, in the same order.

Rules the tests check:

• A request's locale depends only on its own header, never on the requests before it.
• Take the header up to its first ,, the visitor's top choice. Drop everything from the first ;, which is the weight, like ;q=0.9. Trim whitespace from both ends and lowercase what is left. That is the tag.
• The primary part is the tag up to its first -, or the whole tag when it has no -.
• If the tag is not empty and is in supported, use the tag.
• Otherwise, if the primary part is not empty and is in supported, use the primary part.
• Otherwise use "en", even when "en" is not in supported.