Model/packages

Shared packages

Workspace packages consumed by services/*. Each package is its own Python distribution with its own pyproject.toml; services import via the workspace dependency mechanism ({ workspace = true }).

Package	Purpose
domain/	Shared domain types — Property, BaselinePerformance, Plan, Scenario, EpcPropertyData, etc. No persistence, no IO, no business logic.
repos/	Persistence layer — one repo per aggregate. Owns the SQL. Depends on domain.
fetchers/	External API clients (gov EPC, Ofgem, Google Solar, etc.). Depend on domain for response shapes.
utils/	Cross-cutting infra — logging, S3, CloudWatch URL builders, SQS task helpers.

Adding a new shared package

Only when a real second consumer materialises. Don't pre-shatter (repos-epc, repos-property, ...) — split when a deployment needs to drop a dep, not before.

See ../ara_backend_design.md §11 for the broader monorepo layout and ../CONTEXT.md for the domain glossary that names the types living in domain/.