Enumerate a connection's catalog and stage what it finds as catalog sources.

Runs the provider's connector over a bounded window and upserts each item, so repeating the call is safe and reports how many rows were new. YouTube and Drive need external_account_id (the channel or folder) the first time, since consent is account-wide; send it in the body once and it is remembered. A connection that is not active is validation_error, an unknown one is not_found, and a provider with no connector here is ENGINE_PENDING. Requires the explicitly minted bernayser:write scope; bernayser:read permits safe projections and bernayser:write permits mutations. This BERNAYSER operation is quota-neutral. While dark it returns not_found, and a valid key without the required scope receives scope_missing. Fix a non-retryable request or credential before retrying; for rate_limited or service_unavailable, wait for retry_after_sec and retry once.