How to combine conventions buildSrc, platform and versions in gradle 7.3

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Hi, I am trying to find a useful reusable multiproject structure, using buildSrc, conventions and platform subprojects.

What I have now is:

root
|--- buildSrc/
|--- build-conventions/
|     |--- src/main/groovy/
|     |     |--- Catalog.groovy             # interface Libraries {static guava = 'com.google.guava:guava:31.0.1-jre'}
|     |     |--- example-convention.gradle  # dependencies { implementation Libraries.guava }
|     |     |--- dummy-convention.gradle    # // empty file
|--- platform/
|     |--- build.gradle   
|--- example/
|     |--- build.gradle   # plugins { id("example-convention") }
|--- settings.gradle      # includeBuild("build-conventions")

I wanted to use constants defined in Catalog.groovy within the platform project to define constraints.
The only way I could get that to work in platform/build.gradle is:

plugins {
    id "java-platform"
    id("empty-convention") // only using this, I can use Libraries.guava from Catalog.groovy
}

dependencies {
    constraints {
        api Libraries.guava
    }
}

I am not sure whether I am using well-defined behavior or a loophole.
But even this does not allow using the Catalog.groovy constants within buildSrc. If I move it to buildSrc, then the convention project do not see the constants defined in Catalog.groovy.

Is there any cleaner way in gradle 7 to provide build constants such as in the Catalog.groovy to all of: subproject, platform subprojects, convention plugins, buildSrc?

Or should I stop using buildSrc altogether when using composite builds?

Where would incubating Catalog strict dependencies be visible within the project graph?