Cross-provider links prove fixture identity only

Status: Accepted.

Bifrost may publish a Betfair event ID in an event's mutable externalIds. The current, unambiguous value is authoritative evidence that the Bifrost and Betfair fixtures represent the same real-world event, so Hannibal groups their provider sources and markets under one catalogue match. Duplicate copies of the same ID are harmless. No ID, a self-reference, or multiple distinct Betfair IDs is not sufficient evidence and leaves the event Bifrost-only. A newer Bifrost event may remove or retarget the link; older versions cannot reverse that transition.

The link does not establish that Bifrost's tournament and Betfair's competition are the same taxonomy. Catalogue ingestion may choose the linked match's one display parent deterministically, preferring an explicit display configuration and a specific tournament over a generic bucket, but it must not move either tournament's sibling matches or sources, transfer display configuration, archive a tournament, or create a permanent redirect. Admin pins remain authoritative.

This supersedes the tournament-wide cascade previously inferred from one linked fixture. Current ingestion ignores an old cross_provider_match_identity redirect and revives that provider's tournament for its current observations, preventing new fixtures from extending the pollution. Finished/history-only rows still require a separate, audited reconciliation. Betfair catalogue APIs may corroborate an active event or competition, but cannot manufacture a missing Bifrost relationship and omit closed-market history, so they are not an unlink or tournament-merge authority.