Could auto-detect the type of project in the repository and run a common plan for that kind of project
Easy for Rust, but hard in general. It'd be OK to support just one or two common types of project.
Could also be provided as a tool that developers can run to add a CI specific plan file.
Example: if repsitory contains Cargo.toml at the root, assume it's a Rust project, and run the following:
cargo clippy --all-targets --workspace -- --deny warnings
carbo build --all-targets --workspace
cargo test --workspace
That will work for most Rust projects.