There are no events at any version, so every integration polls. Concretely: rules run at import time only, and when a rule fails to match there is no signal — a script has to re-scan the transaction list on a timer to find rows that arrived unlinked or uncategorized.

Webhooks on transaction created and transaction updated would replace all of that polling. A third event when a recurring item's expected date passes with no matching transaction would be even better, since that is the failure users actually care about and it is currently invisible until someone looks.