refetchInterval does not send "update" trigger

Environment

  System:
    OS: macOS 14.3
    CPU: (12) arm64 Apple M2 Pro
    Memory: 2.55 GB / 32.00 GB
    Shell: 3.2.57 - /bin/bash
  Binaries:
    Node: 18.18.0 - ~/.nvm/versions/node/v18.18.0/bin/node
    Yarn: 1.22.19 - ~/.nvm/versions/node/v18.18.0/bin/yarn
    npm: 10.3.0 - ~/.nvm/versions/node/v18.18.0/bin/npm
    pnpm: 8.7.6 - ~/.nvm/versions/node/v18.18.0/bin/pnpm
    bun: 1.1.8 - ~/.nvm/versions/node/v18.18.0/bin/bun
  Browsers:
    Chrome: 125.0.6422.78
    Safari: 17.3

Reproduction URL

https://github.com/sandervspl/next-auth-refetchinterval

Describe the issue

I might be misunderstanding the point of refetchInterval, but currently it does not pass a value to the "trigger" prop in the JWT callback. The update() function DOES have a "update" value on trigger in the JWT callback.

When I read the docs (https://next-auth.js.org/getting-started/client#refetch-interval) there is a link to an "alternative" option that uses the update() function to achieve the same thing. So my understanding is that refetchInterval should also fire with an "update" trigger, just like the update() function does.

How to reproduce

1. Clone the repo
2. npm install
3. npm run dev
4. go to http://localhost:3000/
5. Login with any username
6. Check the terminal for logs to see that the jwt callback is fired without a trigger (should be "update")

Expected behavior

I expect the JWT callback trigger to have a value of update when I read the docs.

Start with the linked reproduction repository and follow its refetchInterval setup, then inspect how the JWT callback receives the trigger during refetchInterval and update() calls. Confirm the behavior in the terminal logs and compare it with the documented expectation. Done means refetchInterval produces an "update" trigger consistently with update().