[spike] investigate consequences of a controller changing from secondary to default (primary)

- What happens if we reconcile a record until ready in secondary mode, then switch to primary?
- What happens if we reconcile a record until ready in primary mode (i.e. records are in a provider somewhere), then switch to secondary? And then delete the delegated records? Clean up orphans in provider?

No files or tests are named. Start by tracing reconciliation when a record changes between secondary and primary modes, including delegated-record deletion and provider cleanup; done means the consequences and orphan-handling behavior for both transition directions are established.

Written by the indexing model from the issue text.