add suggested-nonce endpoint

src/__tests__/routes.test.ts

@@ -373,6 +373,37 @@ describe('API Routes', () => {
       sessionId = result.session.id;
     });
 
+    describe('GET /suggested-nonce/:chainId', () => {
+      it('should return a valid nonce for authenticated user', async () => {
+        const response = await server.inject({
+          method: 'GET',
+          url: '/suggested-nonce/1',
+          headers: {
+            'x-session-id': sessionId,
+          },
+        });
+
+        expect(response.statusCode).toBe(200);
+        const result = JSON.parse(response.payload);
+        expect(result).toHaveProperty('nonce');
+        expect(result.nonce).toMatch(/^0x[0-9a-f]{64}$/i);
+
+        // Verify nonce format: first 20 bytes should match sponsor address
+        const nonceHex = BigInt(result.nonce).toString(16).padStart(64, '0');
+        const sponsorHex = validPayload.address.toLowerCase().slice(2);
+        expect(nonceHex.slice(0, 40)).toBe(sponsorHex);
+      });
+
+      it('should reject request without session', async () => {
+        const response = await server.inject({
+          method: 'GET',
+          url: '/suggested-nonce/1',
+        });
+
+        expect(response.statusCode).toBe(401);
+      });
+    });
+
     describe('POST /compact', () => {
       it('should submit valid compact', async () => {
         const freshCompact = getFreshCompact();

src/routes.ts

@@ -15,6 +15,7 @@ import {
 } from './compact';
 import { getCompactDetails, getAllResourceLocks } from './graphql';
 import { getAllocatedBalance } from './balance';
+import { generateNonce } from './validation';
 
 // Declare db property on FastifyInstance
 declare module 'fastify' {
@@ -484,6 +485,46 @@ export async function setupRoutes(server: FastifyInstance): Promise<void> {
     // Add authentication to all routes in this context
     protectedRoutes.addHook('preHandler', authenticateRequest);
 
+    // Get suggested nonce for a chain
+    protectedRoutes.get<{
+      Params: { chainId: string };
+    }>(
+      '/suggested-nonce/:chainId',
+      async (
+        request: FastifyRequest<{
+          Params: { chainId: string };
+        }>,
+        reply: FastifyReply
+      ) => {
+        if (!request.session) {
+          reply.code(401);
+          return { error: 'Unauthorized' };
+        }
+
+        try {
+          const { chainId } = request.params;
+          const sponsor = request.session.address;
+
+          // Generate a nonce for the sponsor
+          const nonce = await generateNonce(sponsor, chainId, server.db);
+
+          // Return the nonce in hex format with 0x prefix
+          return {
+            nonce: '0x' + nonce.toString(16).padStart(64, '0'),
+          };
+        } catch (error) {
+          server.log.error('Failed to generate nonce:', error);
+          reply.code(500);
+          return {
+            error:
+              error instanceof Error
+                ? error.message
+                : 'Failed to generate nonce',
+          };
+        }
+      }
+    );
+
     // Get available balance for a specific lock
     protectedRoutes.get<{
       Params: { chainId: string; lockId: string };