.NET 7 dependencies and nuget packages managing - asp.net-core

Question

I've started a new .NET 7 project in Visual Studio 2022. The template I used was "ASP.NET Core WebAPI". The project turned out to look like this in the solution explorer:
I can see that there is a dependency upon a series of DLLs in the folder "C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\7.0.2\ref\net7.0". When I browse to this folder and grab, for instance, the "Microsoft.AspNetCore.Http.Abstractions.dll" assembly I see its version as 7.0.22..... which makes sense.
What is weird is that when I click "Manage NuGet Packages" on this project I see absolutely no NuGet package already installed. It looks like this dependency mechanism is something independent of NuGet.
Now I want to create a class library that will encapsulate some common functionality I'd like to share across the projects but it needs to read data from the HttpContext class, which is defined in the "Microsoft.AspNetCore.Http.Abstractions.dll" file. So how should I add this dependency?
Adding it through "dotnet add package Microsoft.AspNetCore.App" command on the class library projects seems like a waste of resources as it adds the entire bundle of dlls and I only care about .Http.Abstractons.dll and it's direct dependencies.
Plus, when I ran the command Visual Studio complained with the warning:
NETSDK1080 A PackageReference to Microsoft.AspNetCore.App is not necessary when targeting .NET Core 3.0 or higher. If Microsoft.NET.Sdk.Web is used, the shared framework will be referenced automatically. Otherwise, the PackageReference should be replaced with a FrameworkReference".
Adding the dll through NuGet worked as Visual Studio was not complaining any more but the version of assembly added was 2.2.0 and not 7.0.2 as in the dotnet package. So technically, the HttpContext referenced in one projects is a different thing to the HttpContext referenced in the other project.
Please help me understand this mechanism and how should I add the dll of interest to my project to be able to access HttpContext in my library.
When should I use dotnet add package and when should I use NuGet packages management? Any good reading on this subject to bring me up to speed from .NET Framework 4.+ to .NET 7 in this area?
As .NET user for the last 10 years or so I feel so lost in the recent developments and find official docs I can find on the web of little use.
I tried adding the Microsoft.AspNetCore.App package through the "dotnet add package" command - Visual Studio complained, plus it pulled the entire bundle of assemblies but I care about only "Microsoft.AspNetCore.Http.Abstractions.dll".
I tried adding the "Microsoft.AspNetCore.Http.Abstractions" NuGet package but the version of assembly added was completely different to the one referenced in the WebAPI project.

Answer 1

What is weird is that when I click "Manage NuGet Packages" on this project I see absolutely no NuGet package already installed.
Those dependencies are determined by the project SDK which can be found in the root element of .csproj:
<Project Sdk="Microsoft.NET.Sdk.Web">
...
</Project>
So how should I add this dependency?
For latest versions of .NET you should reference corresponding SDK via FrameworkReference, for example to reference ASP.NET Core components you should add <FrameworkReference Include="Microsoft.AspNetCore.App"/> to library projects .csproj file as mentioned in the docs (and in the warning):
<Project Sdk="Microsoft.NET.Sdk">
<!--... rest of file-->
<ItemGroup>
<FrameworkReference Include="Microsoft.AspNetCore.App" />
</ItemGroup>
<!--... rest of file-->
</Project>