Post-V1: cross-period entity continuity (name_history) #13

Context

Deferred from Phase 1. The source (Historical Basemaps) has no stable entity identifiers across periods — each of the 53 snapshots is independent. V1 is therefore snapshots-only: each territory id is a slug unique within a snapshot, not stable across years.

Goal

Power the territory panel's name timeline (Roadmap Phase 4) and the name_history field in the ARCHITECTURE.md data model (e.g. Roman Republic → Roman Empire) by resolving entity continuity across snapshots.

Approach (sketch)

• Use the Wikidata QID already attached during enrichment as a cross-snapshot join key.
• Group features sharing a QID across years; derive per-period name spans ({ name, from, to }).
• Handle entities without a QID (~36% today) and many-to-one / splits & merges (empires fragmenting, unions forming) — this is the hard part.

Notes

Significant data-modeling effort with real uncertainty; explicitly post-V1. The pipeline's source isolation and the committed Wikidata cache are the building blocks.

Refs: docs/ARCHITECTURE.md (Territory data model), docs/ROADMAP.md (Phase 4), scripts/pipeline/.