Initial project setup: Add contracts, API definitions, tests, and documentation

- Add Foundry project configuration (foundry.toml, foundry.lock)
- Add Solidity contracts (TokenFactory138, BridgeVault138, ComplianceRegistry, etc.)
- Add API definitions (OpenAPI, GraphQL, gRPC, AsyncAPI)
- Add comprehensive test suite (unit, integration, fuzz, invariants)
- Add API services (REST, GraphQL, orchestrator, packet service)
- Add documentation (ISO20022 mapping, runbooks, adapter guides)
- Add development tools (RBC tool, Swagger UI, mock server)
- Update OpenZeppelin submodules to v5.0.0

api/services/rest-api/src/middleware/idempotency.ts

@@ -0,0 +1,21 @@
+/**
+ * Idempotency middleware
+ * Ensures requests with same idempotency key are only processed once
+ */
+
+import { Request, Response, NextFunction } from 'express';
+// import { redisClient } from '../services/redis';
+
+export async function idempotencyMiddleware(req: Request, res: Response, next: NextFunction) {
+  const idempotencyKey = req.headers['idempotency-key'] as string;
+  
+  if (!idempotencyKey) {
+    return next();
+  }
+  
+  // TODO: Check Redis for existing response
+  // TODO: Store response in Redis for replay
+  // For now, pass through (will be implemented in Phase 6)
+  next();
+}
+