See https://weblogs.asp.net/ricardoperes/net-8-dependency-injection-changes-keyed-services

Design:

1. A new [Service<TKey>(key)] attribute will be emitted. Use of the attribute reflects an explicit opt-in to keyed services and will cause a build failure if the referenced DI package isn't v8+ (seems reasonable to me).

2. Using [FromKeyedServices] in a type constructor will (as expected) result in resolving with the given key.

3. To keep the MEF-based decoupling in libraries, [Export("contract")] and [Import("contract")] will both be considered as hints for a string-based keyed service (both for registering and resolving, respectively).

4. Lifetime considerations remain as before: default is Singleton for [Service], and transient for [Export] unless a [PartCreationPolicy(CreationPolicy.Shared)] is used (to keep MEF conventions).