Function createMessagingRegistry

createMessagingRegistry(options?: MessagingRegistryOptions): MessagingRegistry
Create the shell's provider registry.

The registry owns one backend per enabled provider and hands out a single composite backend for the NAP dm service. Preferences restored at construction are applied lazily: a provider that appears in the saved enabled list is enabled the moment it is registered, if it is available; an unavailable one stays disabled and reports why through list().

close() closes every backend without touching the preferences, so a shutdown never erases what the user chose. A closed registry is not reused.
Parameters
- options: MessagingRegistryOptions = {}
  Saved preferences and a change listener.
Returns MessagingRegistry
A MessagingRegistry.
Example
```
const registry = createMessagingRegistry({
  preferences: load(),
  onChange: (prefs) => save(prefs),
});
registry.register(createPrivateMessagesProvider(deps));
registry.enable('private');
registry.setDefault('private');
```