Domain: billing

Curated entry point for the billing bounded context.

Owner

Founder + agents (Phase 1).

Mission

Owns money flowing in to Astrix Trading: Stripe integration, evaluation purchases, instant-funded purchases, subscriptions, resets, refunds, coupon redemption, fraud signals, and invoice generation. Boundary: billing owns the cash-in side of the ledger; account-state changes triggered by purchase live in accounts; cash-out flows live in payouts.

Code paths

• Application code: apps/api/src/modules/billing/
• Domain logic (pure): packages/domain/pricing/
• Contracts: packages/contracts/api/billing.ts, packages/contracts/events/billing.ts
• External clients: packages/clients/stripe/
• Database schemas owned: billing (Charge, Subscription, Invoice, Refund, Coupon, FraudSignal, StripeWebhookEvent)

PRD chapters that touch this domain

• 02-business-model.md - pricing tiers, programs, unit economics
• 05-commerce-purchase.md - purchase funnel, checkout, resets, refunds
• 10-integrations.md - Stripe integration spec
• 11-data-model.md - billing entities

TDD chapters

(Empty - will populate as TDDs arrive.)

ADRs that affected this domain

• ADR-0001 (transversally applies)

Service interfaces this domain exposes

export interface BillingService {
  // createCheckoutSession(userId, productId, couponCode?): Promise<CheckoutSession>
  // handleStripeWebhook(payload, signature): Promise<void>
  // refundCharge(chargeId, reason): Promise<Refund>
  // listInvoices(userId): Promise<Invoice[]>
  // applyCoupon(code, productId): Promise<DiscountedPrice>
  // (full surface defined during billing TDD)
}

Events this domain produces / consumes

Direction	Topic	Triggered by
produces	billing.payment.completed	Successful Stripe charge
produces	billing.payment.failed	Failed / declined charge
produces	billing.refund.processed	Refund issued
produces	billing.subscription.updated	Subscription state change
produces	billing.fraud.flagged	Stripe Radar / our fraud signal
consumes	accounts.account.state_changed	Triggers reset eligibility / refund evaluation

External integrations

• Stripe - charges, subscriptions, refunds, Radar (fraud), tax (per Q-I in docs/PRD/10-integrations.md)

Runbooks for this domain

(Empty - will populate when alerts are defined in Section 17.6.)

On-call

To be filled in Section 17.6.

Cross-domain dependencies

• This domain calls: identity (actor lookup), accounts (post-purchase account provisioning).
• This domain emits events consumed by: accounts (provision on payment.completed), audit (every payment event), notifications (receipts, refund confirmations), admin (revenue dashboards, support-side refund tooling).