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openspec/changes/enterprise-currency/proposal.md

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+# OpenSpec Change: enterprise-currency
+
+- **Change ID**: enterprise-currency
+- **Package**: `@suaveplan/currency`
+- **Category**: finance
+- **Target path**: `finance/currency/currency`
+- **Status**: PROPOSED
+- **Date**: 2026-04-24
+- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/currency.md`
+
+---
+
+## Summary
+
+Deliver `@suaveplan/currency` on the genesis branch from scratch at enterprise quality. The package is a currency conversion engine with pluggable `CurrencyProvider` interface, TTL-based `RateCache`, automatic BFS cross-rate triangulation (shortest-path over the cached-rate graph), inverse-rate calculation, per-provider circuit breaker, `AbortSignal` cancellation, batch convert, and a `setVirtualRate` live-update API. Returns typed `ConversionResult` with provenance (`providerName`, `triangulatedThrough`). Ships two reference providers: `InMemoryProvider` and `createStaticProvider`.
+
+---
+
+## Current-state audit (genesis)
+
+Does not exist on genesis — fresh build.
+
+---
+
+## Available workspace deps on genesis
+
+| Package | Role |
+|---|---|
+| `@suaveplan/error` (`workspace:^`) | Typed `CURRENCY.*` error codes |
+| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `EventBusLike` |
+| `@suaveplan/events` (`workspace:^`) | Virtual-rate change events |
+| `@suaveplan/retry` (`workspace:^`) | Circuit-breaker + backoff |
+| `@suaveplan/logger` (`workspace:^`) | Structured logs |
+| `zod` (`catalog:forms`) | Options validation |
+| `@opentelemetry/api` (`catalog:observability`) | Spans + counters |
+| `tslib` (`catalog:build`) | Runtime helpers |
+
+Dev dep: `@suaveplan/money workspace:^` (for `MoneyLike` type in tests).
+
+---
+
+## Public API surface (from main branch enterprise spec)
+
+```ts
+class CurrencyConverter {
+  constructor(config: ConverterConfig)
+  convert(from: string, to: string, amount: MoneyLike | number, options?: ConvertOptions): Promise<ConversionResult>
+  convertAmount(from: string, to: string, amount: number, options?: ConvertOptions): Promise<ConversionResult>
+  convertBatch(requests: Array<{from: string; to: string; amount: number}>): Promise<ConversionResult[]>
+  setVirtualRate(symbol: string, rate: number): void
+  invalidateCache(from?: string, to?: string): void
+}
+
+class RateCache {
+  get(from: string, to: string): ExchangeRate | undefined
+  set(from: string, to: string, rate: ExchangeRate): void
+  prune(): void
+  invalidate(from?: string, to?: string): void
+}
+
+function createStaticProvider(rates: Record<string, Record<string, number>>): CurrencyProvider
+class InMemoryProvider implements CurrencyProvider { setRates(rates: ExchangeRate[]): void }
+
+interface ConversionResult {
+  amount: number
+  rate: number
+  inverseRate: number
+  rateAgeMs: number
+  providerName: string
+  triangulatedThrough: string[] | null
+}
+
+interface ConverterConfig {
+  providers: CurrencyProvider[]
+  defaultBase?: string
+  cacheTtlMs?: number
+  maxRetries?: number
+  logger?: LoggerLike
+}
+
+interface CurrencyProvider {
+  name: string
+  supportsFiat: boolean
+  supportsCrypto: boolean
+  fetchRates(options: RateFetchOptions): Promise<RateFetchResult>
+  isHealthy?(): boolean
+}
+```
+
+### Error codes
+
+```ts
+type CurrencyErrorCode =
+  | 'CURRENCY_PROVIDER_UNAVAILABLE'
+  | 'CURRENCY_UNSUPPORTED_PAIR'
+  | 'CURRENCY_TRIANGULATION_IMPOSSIBLE'
+  | 'CURRENCY_CONVERT_ABORTED'
+  | 'CURRENCY_INVALID_CONFIG'
+
+function registerCurrencyErrorCodes(): void
+```
+
+---
+
+## New additions for genesis
+
+- **BFS triangulation** in `src/engine/triangulate.ts`
+- **Circuit breaker** per provider in `src/engine/circuit-breaker.ts` using `@suaveplan/retry`
+- **`convertBatch`** — coalesces required rate fetches
+- **`setVirtualRate` + change events** via `@suaveplan/events`
+- **`AbortSignal` on `convert`**
+- **Zod schemas** for `ConverterConfig`, `ConvertOptions`
+- **OTel** spans per convert, cache-hit counter, triangulation-path histogram
+
+---
+
+## File layout
+
+```text
+finance/currency/currency/
+  package.json
+  tsconfig.json
+  vitest.config.ts
+  src/
+    index.ts
+    error-codes.ts
+    constants/index.ts
+    types/
+      currency.types.ts
+      currency.types.md
+    engine/
+      converter/
+        converter.ts
+        converter.md
+        converter.types.ts
+        converter.test.ts
+        index.ts
+      rate-cache/
+        rate-cache.ts
+        rate-cache.md
+        rate-cache.test.ts
+        index.ts
+      triangulate/
+        triangulate.ts
+        triangulate.md
+        triangulate.test.ts
+        index.ts
+      circuit-breaker/
+        circuit-breaker.ts
+        circuit-breaker.md
+        circuit-breaker.test.ts
+        index.ts
+    provider/
+      in-memory-provider/
+        in-memory-provider.ts
+        in-memory-provider.md
+        in-memory-provider.test.ts
+        index.ts
+      static-provider/
+        static-provider.ts
+        static-provider.md
+        static-provider.test.ts
+        index.ts
+  tests/
+    integration.test.ts
+    property.test.ts
+```
+
+---
+
+## Impact
+
+Downstream: `@suaveplan/currency-providers` (implements `CurrencyProvider`), `@suaveplan/money` (integration for `MoneyLike`).
+
+**Prerequisites on Verdaccio**: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/events`, `@suaveplan/retry`, `@suaveplan/logger`.