Discover complete lineages with bounded historical exceptions

[iam-brain]

Question

Expand discovery in one isolated PR so the normal 30-day scan remains bounded while exceptional long-lived parents outside that window are pulled from active or archived storage only when transitively referenced by an included descendant.

[iam-brain]

Implemented and locally validated in stacked fork PR #26. Per the map completion rule, this slice does not wait for CI or merge.