My experience of Golang is that dependency injection doesn't really have much benefit. It felt like a square peg in a round hole exercise when my team considered it. The team was almost exclusively Java/Typescript Devs so it was something that we thought we needed but I don't believe we actually missed once we decided to not pursue it.
If you are looking at OpenAPI in Golang I can recommend having a look at https://goa.design/. It's a DSL that generates OpenAPI specs and provides an implementation of the endpoints described. Can also generate gRPC from the same definitions.
We found this removed the need to write almost all of the API layer and a lot of the associated validation. We found the generated code including the server element to be production ready from the get go.
For OpenTofu specifically, having DI for implementing state encryption would have been really nice. Of you look at the PR, a lot of code needed to be touched because the code was entirely procedural. Of course, one could just make a global variable, but that is all sorts of awful and makes the code really hard to test efficiently. But then again, this is a 300k line project, which in my opinion is way beyond what Go is really good for. ContainerSSH with 35k+ lines was already way too big.
I wish I had an answer to that, but I don't know. I only worked on projects of comparable size in Go, Java and PHP. Java was maybe the best for abstractions (big surprise), but it really doesn't lend itself to system-level stuff.
If you are looking at OpenAPI in Golang I can recommend having a look at https://goa.design/. It's a DSL that generates OpenAPI specs and provides an implementation of the endpoints described. Can also generate gRPC from the same definitions.
We found this removed the need to write almost all of the API layer and a lot of the associated validation. We found the generated code including the server element to be production ready from the get go.