refactor: standardize getBillingDbClient helper across all billing files

Apply the same getBillingDbClient helper pattern from grant-credits.ts to:
- balance-calculator.ts (calculateUsageThisCycle)
- credit-delegation.ts (findOrganizationForRepository)
- org-billing.ts (syncOrganizationBillingCycle)

This centralizes the DB client casting logic and removes redundant comments.

Author: brandonkachen

packages/billing/src/balance-calculator.ts

@@ -22,6 +22,10 @@ import type { trackEvent as trackEventFn } from '@codebuff/common/analytics'
 import type { reportPurchasedCreditsToStripe as reportPurchasedCreditsToStripeFn } from './stripe-metering'
 import type { BillingDbConnection } from '@codebuff/common/types/contracts/billing'
 
+const getBillingDbClient = (
+  dbOverride?: BillingDbConnection,
+): BillingDbConnection => (dbOverride ?? db) as BillingDbConnection
+
 export interface CreditBalance {
   totalRemaining: number
   totalDebt: number
@@ -693,8 +697,7 @@ export async function calculateUsageThisCycle(params: {
   deps?: CalculateUsageThisCycleDeps
 }): Promise<number> {
   const { userId, quotaResetDate, deps = {} } = params
-  // Cast to BillingDbConnection to allow either real db or mock to be used
-  const dbClient = (deps.db ?? db) as BillingDbConnection
+  const dbClient = getBillingDbClient(deps.db)
 
   const usageResult = await dbClient
     .select({

packages/billing/src/credit-delegation.ts

@@ -14,6 +14,10 @@ import type { ConsumeCreditsWithFallbackFn, BillingDbConnection } from '@codebuf
 import type { Logger } from '@codebuff/common/types/contracts/logger'
 import type { ParamsOf } from '@codebuff/common/types/function-params'
 
+const getBillingDbClient = (
+  dbOverride?: BillingDbConnection,
+): BillingDbConnection => (dbOverride ?? db) as BillingDbConnection
+
 export interface OrganizationLookupResult {
   found: boolean
   organizationId?: string
@@ -47,8 +51,7 @@ export async function findOrganizationForRepository(params: {
   deps?: FindOrganizationForRepositoryDeps
 }): Promise<OrganizationLookupResult> {
   const { userId, repositoryUrl, logger, deps = {} } = params
-  // Cast to BillingDbConnection to allow either real db or mock to be used
-  const dbClient = (deps.db ?? db) as BillingDbConnection
+  const dbClient = getBillingDbClient(deps.db)
 
   try {
     const normalizedUrl = normalizeRepositoryUrl(repositoryUrl)

packages/billing/src/org-billing.ts

@@ -19,6 +19,10 @@ import type { BillingTransactionFn, BillingDbConnection } from '@codebuff/common
 import type { OptionalFields } from '@codebuff/common/types/function-params'
 import type { GrantType } from '@codebuff/internal/db/schema'
 
+const getBillingDbClient = (
+  dbOverride?: BillingDbConnection,
+): BillingDbConnection => (dbOverride ?? db) as BillingDbConnection
+
 // Minimal structural type that both `db` and `tx` satisfy
 // Note: This is intentionally defined locally rather than imported from billing.ts
 // because it needs to be compatible with real Drizzle types (PgTransaction, etc.)
@@ -42,8 +46,7 @@ export async function syncOrganizationBillingCycle(params: {
   deps?: SyncOrganizationBillingCycleDeps
 }): Promise<Date> {
   const { organizationId, logger, deps = {} } = params
-  // Cast to BillingDbConnection to allow either real db or mock to be used
-  const dbClient = (deps.db ?? db) as BillingDbConnection
+  const dbClient = getBillingDbClient(deps.db)
   const stripe = deps.stripeServer ?? stripeServer
 
   const organization = await dbClient.query.org.findFirst({