Not finding bower components with vaadin-spring-boot-starter

Flow
1

I am extending an existing Spring application with a Vaadin-based admin UI. By following the quickstart example on https://spring.io/guides/gs/crud-with-vaadin/ (and other similar guides), I am not able to deploy this properly, the client fails to find most/all resources:

Instead of deploying to the context root, I am deploying it under /admin by adding the following to my application.properties:

vaadin.urlMapping=/admin/*

Is there a build-step I am missing, or something else that is wrong? The folders frontent and bower_component are not a part of my project, and does not seem to be generated either with mvn:install

edit:
After some digging I found this GitHub ticket: https://github.com/vaadin/flow/issues/4356
From what I understand, it is non-trivial to use Vaadin Flow and at the same time have something else listing on the root (“/”). In my case, this is already occupied by existing parts of the project (which is SPring-based, not Vaadin). And this is even not considered a bug, but intended features (ref the replies in that ticket). I think this means i am not able to use Vaadin Flow for creating just the admin console.

2

Is anyone able to confirm that you can (or can not) use Vaadin Flow while at the same time reserving the context root for something else (in this case, a Spring controller)? That is the only difference I can see between my project that is unable to load the resources indicated in the screenshot from the original post and the quick start examples (including Spring’s own for Spring Boot).

Using Vaadin 8 is a solution that would work, but I would like to confirm that Vaadin Flow is not an option first before investing time in a Vaadin 8 implementation.