How do you integrate an Agile work stream into your project WBS?
This is a very broad question to answer, and from what you said in your post, it might be made even broader by a lack of familiarity with Agile practices.
A WBS is not something that you would normally find in Agile practices, like Scrum, for example, because a WBS is synonym with a big design upfront. With a Work Breakdown Structure you decompose your project into smaller pieces. Those will basically be your deliverables. Sometimes, people also include actions within the WBS, as an indication of how to make those deliverables happen.
Agile practices argue that this is most likely a waste. You are trying to plan your project at the beginning of the project, when you know the least about the project. Things will inevitably change once you start the project and some things on the WBS might not be needed, others might suffer modifications, while some new ones might show up. Agile says you should probably not do that, but instead wait until you have more information and more feedback on what the product should do. That will allow you to plan better and to figure out what deliverables are actually needed.
It seems to me from your question, that you want to build the WBS then use Scrum to build everything. Scrum doesn't work with a WBS, it works with a Product Backlog. You might say that a product backlog is just another form of organizing a work breakdown structure (for example, you might also say epics in a backlog might be equivalent to work packages in WBS), but a backlog is usually not defined as detailed as a WBS. The WBS should include all the scope of the project, while a backlog usually includes a higher perspective. In other words, compared to the WBS, the backlog might contain just the higher levels of the WBS and not go deeper into other levels. You go deeper as you need to. After each iteration or release, and after each dose of feedback you receive, you decide on what to go deeper next.
With a WBS you decide "this is all we are going to build". With an Agile approach, you build the thing incrementally, in iterations. A WBS works better when you know exactly what you want, an Agile approach works better - as you said yourself - "under uncertainty where adaptation is required as the work progresses".
So because of the things I mentioned above, you might integrate Scrum with your WBS, but most likely you won't end up with Scrum or an Agile implementation, but just with Waterfall performed in sprints. A more Agile practice of decomposing work than using a somewhat rigid WBS (that contains the total scope of work to be carried out), might be User Story Mapping, so maybe have a look at that for reference.