references/schema-contracts.md

# Schema, grain, types and consumer contracts

For every dataset document owner, source, target, intended grain, keys, type/nullability, allowed values, time semantics, currency/unit semantics, latest acceptable source version, update/delete behavior and consumer SLA.

## Key/cardinality review
- Identify unique rows in each table **before** joining; one-to-many child tables may need aggregation at parent grain.
- Check FK nulls/unmatched rows, unexpected duplicate primary keys, temporal overlap for SCD2 and point-in-time join logic.
- Numeric conversions and timezone effects can change totals even when row counts match.

## Schema evolution
Define additive vs breaking changes, defaults for new nullable columns, type widening/narrowing, rename/drop policy and compatibility with streaming state and downstream models.

## Acceptance contract
Provide fixture queries for uniqueness, nullability, source-to-target conservation, reconciliation and downstream metric invariants. Keep an owner and severity per contract.