Identities Overview Metrics

Secondary directory metrics with independent recovery from core rows.

TOS-2838 reference implementation for user-initiated cancellation. This is the route the ticket opened on - the slowest authenticated read in the product, and the one where a user is most likely to give up waiting.

The caller chooses the operation id and sends it up front, because a non-streaming response cannot hand one back while the request it would cancel is still running. Sending no header simply means no Cancel is offered, so every existing caller keeps working unchanged.

Registration and release both use their own short-lived session rather than db: after a cancel lands, db's transaction is aborted and cannot be written to, so bookkeeping on it would fail exactly when it matters.