Clearing State subscriptions

If you clear all state subscriptions, the subscriptions persist until a new subscription is added. Similarly, if you try to remove the final subscription it persists until a new subscription is added.

Start by locating the state-subscription handling and reproduce clearing all subscriptions and removing the final subscription. The fix is done when both operations remove the subscriptions immediately, without requiring a new subscription to be added; add or update regression coverage if the relevant tests are found.

Written by the indexing model from the issue text.