Have you explored building with Bazel? What you describe as a problem is roughly what Bazel solves: Polyglot complex builds from fully vendored deps.
Just pointing this out because I had a fair share of issues with Cargo and ultimately moved to Bazel and a bit later to BuildBuddy as CI. Since then my builds are reliable, run a lot faster and even stuff like cross compilation in a cluster works flawlessly.
Obviously there is some complexity implied when moving to Bazel, but the bigger question is whether the capabilities of your current build solution keep up with the complexity of your requirements?
Just pointing this out because I had a fair share of issues with Cargo and ultimately moved to Bazel and a bit later to BuildBuddy as CI. Since then my builds are reliable, run a lot faster and even stuff like cross compilation in a cluster works flawlessly.
Obviously there is some complexity implied when moving to Bazel, but the bigger question is whether the capabilities of your current build solution keep up with the complexity of your requirements?