ADR-0002. DiscriminationType as authoritative tax classification (dual-write taxTypeId)

Field	Value
Status	Accepted
Date	2026-04-15
Deciders	taxation-team
Supersedes	—

Context

• The system has a generic DiscriminationType classifier (scopes for inventory, finance, license, and tax_classification).
• The legacy TaxType entity in the pricing schema also classified taxes (000_VAT, 400_PIT, ...), duplicating that concept.
• TaxGroupItem and Tax need one classification source; existing pricing/calculation code still reads Tax.taxTypeId.
• We want a single, scope-partitioned catalogue without breaking pricing immediately.

Decision

TaxGroupItem.discriminationTypeId and Tax.discriminationTypeId (both notNull) are the authoritative tax classification. During provisioning we dual-write: each Tax keeps the new discriminationTypeId and the legacy taxTypeId (nullable) so existing pricing reads continue to work. Discrimination types under scope tax_classification are seeded by taxation-0001-seed-discrimination-types.ts.

Consequences

Pros	Cons
Single classifier catalogue across domains	Two columns to keep aligned during the transition
Tax.taxTypeId stays nullable — no hard break for pricing	Reconciliation logic needed to map DiscriminationType → TaxType
New tax classes added via discrimination seeds, not schema	TaxType table lingers until pricing migrates fully

Alternatives Considered

Option	Pros	Cons	Why rejected
Keep TaxType only	No migration	Duplicate classifier concept; no cross-domain reuse	Diverges from DiscriminationType strategy
Drop taxTypeId immediately	Clean schema	Breaks pricing reads in-flight	Too risky without coordinated pricing change
Separate tax-only classifier table	Focused	Yet another classifier; same duplication problem	Reuse beats new table

References

• packages/core/src/models/schemas/tax/tax-group-item/schema.ts (discriminationTypeId)
• packages/core/src/models/schemas/pricing/tax/schema.ts (taxTypeId nullable + discriminationTypeId)
• packages/core/src/models/schemas/public/discrimination-type/constants.ts:DiscriminationTypeScopes.TAX_CLASSIFICATION
• packages/taxation/src/services/tax-provisioning.service.ts (dual-write loop)
• packages/taxation/src/migrations/processes/taxation-0001-seed-discrimination-types.ts