When members are bulk-deleted we previously left their entries in the\nmailListAudit collection behind. That meant unsubscribe/audit history\nkept showing the bare Mongo ObjectId in the Brevo Unsubscribes view\n(no name, no email — just the deleted member's ID), and more\nimportantly it left identifiable records hanging around past the point\nwhere the member record itself was gone. Not appropriate for a Ramblers\nendorsed project.
\nCascade — MemberBulkDeleteService now calls a new server endpoint\n(POST /api/database/mail-list-audit/delete-by-members) immediately\nafter deleting members. Audit rows for those member IDs are removed\nin a single deleteMany. Errors here log but don't fail the whole\nbulk-delete operation, so the member deletion is never left half\ndone.
\nOrphan sweep — same flow then calls\nPOST /api/database/mail-list-audit/delete-orphans which removes any\naudit row whose memberId no longer matches an existing member.\nBackstop for any data that drifts in via other delete pathways or\ndirect database edits.
\nOne-off migration — 20260427100000-purge-orphan-mail-list-audit.ts\ndoes the same orphan sweep once on next deploy so historical\npre-cascade orphans are cleaned up before the new cascade goes\nlive. Idempotent — safe to re-run.
\nMongoDB doesn't enforce foreign keys, so this is application-level\ncascade rather than DB-level. The migration is the necessary cleanup\nof pre-existing orphans before activating the new behaviour.
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