mhart / reproduce-next-parallel-context

To reproduce this error:

1. Run npm preview in one tab.
2. In the next tab npm run break (may need to run a couple of times if you observe no errors)
3. Observe TypeError: Cannot read properties of null (reading 'useContext') in the logs + 500 internal server error

To show the error is fixed (requires Node.js v22+):

1. Run npm preview:fixed in one tab.
2. In the next tab npm run break
3. Observe both requests succeed