Lando to Sail creates CORS errors

I'm trying to convert our app to use Sail instead of Lando on WSL.

• I've installed Sail and published its Docker files so that I can add opentelemetry to it. No problem there.
• I updated the docker-composer.yml file to give that service a new name.
• I've run sail build --no-cache
• I've updated the <php> section of phpunit.xml to go back to <envs rather than <servers and set DB_CONNECTION to pgsql.
• I've updated .env so APP_URL is http://localhost.

Running sail npm run dev seems to run fine. However, no matter what I do, I get CORS errors when attempting to visit the page in a browser.

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:3009/@vite/client. (Reason: CORS request did not succeed). Status code: (null).

Module source URI is not allowed in this document: “http://localhost:3009/@vite/client”. login:19:80

It appears to redirect to /login just fine and show the name of the app in the browser's tab, so I know it's partially working. But this CORS thing is stopping it cold and I don't know what to do to get past it. Can anyone please help?

EDIT

Even stranger, when cancel out of sail npm run dev, then the app works fine! (Maybe because I ran sail num run build at some point after posting this.) But the moment I start up sail npm run dev, I again get the CORS errors. So confusing!