useChat onData is not triggered when used with a shared chat context context

[jonnyhd]

When using a shared context useChat's onData callback is not triggered by transient data messages sent from the server.

The onData for the Chat class (which is at the context level) does trigger.

I've recreated the issue in the repo below, using ai sdk template files.

https://github.com/jonnyhd/on-data-issue

Seeking guidance on whether my assumptions are correct before raising as an issue.

May be related to: #8549

[gr2m]

fyi I created an issue for this discussion:
#8597

We'll have a look over there.