Automatically generating pull requests for subproject changes

Question

We have a set of subprojects that are developed independently, but need to be coordinated on interface changes. In addition, a "main" project records consistent states of these subprojects.

Maintaining this is somewhat tedious, despite a lot of shell scripting.

The rules are:

• subproject commits should be advanced only to a direct descendant if possible (so either the change is atomic, or a merge commit needs to be generated in the subproject)
• if advancing a subproject commit does not break the build of the main project, a single commit should be generated that only includes this change
• if advancing a subproject commit does break the build of the main project, try advancing other subprojects alone first
• if no solution can be found that only changes one subproject, find a combination of multiple subprojects that need to be advanced together.

Usually, interface changes are submitted to all affected subprojects at the same time, and integrators are aware of the dependency and merge them close to each other as well, so we pretty much always have a consistent state even if this is not properly enforced (in other words, the process is bad but works), but the main project is quite often out of date, especially when multiple things get deployed to production on a Friday afternoon.

Is there a tool similar to GitHub's Dependabot that is able to go back and modify the merge request it generated when there is a build failure, and that can be taught to advance only small steps (so git bisect on the "main" project keeps working)?