⚙️ perf: reduce first-load MongoDB round trips (#14101)

* perf(api): reduce first-load database round trips

* docs: move agent guidance to claude docs

* refactor(api): move message validation into api package

* fix(api): narrow active generation job lookup

* fix(api): preserve omitted source identity

api/server/services/Config/loadConfigModels.spec.js

@@ -104,6 +104,7 @@ describe('loadConfigModels', () => {
       role: 'USER',
       userId: 'testUserId',
       tenantId: 'tenant-a',
+      idOnTheSource: undefined,
     });
   });