Loader request not cancelled when streaming promises Single Fetch

[timvandam]

Reproduction

https://stackblitz.com/edit/remix-run-remix-869qzk?file=package.json,app%2Froutes%2F_index.tsx,app%2Froot.tsx

System Info

System:
    OS: macOS 14.3
    CPU: (16) arm64 Apple M3 Max
    Memory: 2.78 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.11.1 - ~/.nvm/versions/node/v20.11.1/bin/node
    npm: 10.2.4 - ~/.nvm/versions/node/v20.11.1/bin/npm
    pnpm: 9.5.0 - ~/.nvm/versions/node/v20.11.1/bin/pnpm
  Browsers:
    Chrome: 126.0.6478.183
    Safari: 17.3

Used Package Manager

npm

Expected Behavior

I am encountering issues with Single Fetch when a fetcher is called while a loader is still streaming down deferred promises. If I make the loader/action take arbitrarily long (e.g., awaiting a timeout of 10 seconds) and submit a form multiple times, all requests but the last are correctly aborted. However, this does not happen if a promise is being streamed down. This seems like a bug in Single Fetch. In my case this results in issues with optimistic UI, as data returned by useLoaderData is not in sync with the data returned by the last loader invocation.

Actual Behavior

I would expect the loader request to be cancelled