Append-only history of person properties and cohort definitions, since
the free tier overwrites the live person / prunes data. A new row is
written only when the payload changes (hash compare), so the tables stay
a compact change-timeline rather than a daily full copy.
- `PosthogPersonSnapshot` (personId join key to PosthogEvent.personId,
all distinct_ids, properties JSONB, propertiesHash).
- `PosthogCohortSnapshot` (cohortId, name, count, filters, stateHash).
- `listPersons` / `listCohorts` REST helpers (next-pagination) in posthog.ts.
- `stableHash` (sorted-key JSON hash) in hash.ts for change detection.
- `posthog-identity-archive` job wired @03:00 daily. Latest-hash lookup
via one DISTINCT ON query, inserts only changed rows via createMany.
Verified against prod: 242 persons → 242 snapshots on first run, 0 on
immediate re-run (change detection). 0 cohorts currently → graceful no-op.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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