fix(api): prevent self-loop routes, map P2003 to 400, forward DELETE error body

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/modules/routes/routes.service.spec.ts

@@ -87,6 +87,19 @@ describe('RoutesService', () => {
       mockPrisma.syncRoute.create.mockRejectedValueOnce(p2002);
       await expect(service.create('grp_1', 'grp_2')).rejects.toThrow(ConflictException);
     });
+
+    it('throws BadRequestException when source and target are the same group', async () => {
+      await expect(service.create('grp_1', 'grp_1')).rejects.toThrow(BadRequestException);
+    });
+
+    it('throws BadRequestException when a group ID does not exist (Prisma P2003)', async () => {
+      const p2003 = new Prisma.PrismaClientKnownRequestError('Foreign key constraint', {
+        code: 'P2003',
+        clientVersion: '6.0.0',
+      });
+      mockPrisma.syncRoute.create.mockRejectedValueOnce(p2003);
+      await expect(service.create('grp_1', 'bad_grp')).rejects.toThrow(BadRequestException);
+    });
   });
 
   describe('remove', () => {

apps/api/src/modules/routes/routes.service.ts

@@ -23,14 +23,22 @@ export class RoutesService {
     if (!sourceGroupId || !targetGroupId) {
       throw new BadRequestException('sourceGroupId and targetGroupId are required');
     }
+    if (sourceGroupId === targetGroupId) {
+      throw new BadRequestException('Source and target groups cannot be the same');
+    }
     try {
       return await this.prisma.syncRoute.create({
         data: { sourceGroupId, targetGroupId },
         include: routeInclude,
       });
     } catch (e) {
-      if (e instanceof Prisma.PrismaClientKnownRequestError && e.code === 'P2002') {
-        throw new ConflictException('A route between these groups already exists');
+      if (e instanceof Prisma.PrismaClientKnownRequestError) {
+        if (e.code === 'P2002') {
+          throw new ConflictException('A route between these groups already exists');
+        }
+        if (e.code === 'P2003') {
+          throw new BadRequestException('One or both group IDs do not exist');
+        }
       }
       throw e;
     }