Function compute_env_delta 

pub fn compute_env_delta(
    ctx: &Ctx,
    registry: &Registry,
    cwd: &Path,
) -> Result<EnvDelta>

Compute the env delta for the directory cwd: for each backend with an active + installed version, collect its bin dirs and exec env. Invalid dynamic-tool inventory aborts activation instead of producing a partial environment that could route around the configured tool.