[discussion] validation of core exposed services/shared instances

If core exposed services/shared instances are not initialized correctly or are not ready to use, should we block the registration of extensions? Or we should let the extension make the validation when registering itself to Eventhub and decide how to handle the other logic.

Start by tracing initialization of the core exposed services and shared instances, then follow extension registration through Eventhub. Determine whether registration should be blocked when core services are unavailable or whether each extension validates them, and document the chosen behavior and handling of failure cases.

Written by the indexing model from the issue text.