Node.js Backend Developer / SaaS Developer for a written mobile API and offline sync spec

We run a multi-tenant B2B SaaS for workforce management. Our customers are US service businesses whose crews spend the day on job sites, and the web platform is where their office schedules jobs, assigns crews, tracks time and bills. We are now building a mobile companion app for those crews - React Native, offline-first, on company-issued Android and iOS phones. The app side is settled in writing: the stack has been audited and the design has been scoped. What is not settled is the backend underneath the app. Until now our platform has only served people in an office with a good connection. The app will talk to it from basements, parking garages and trucks, often with no signal for hours, and the time records it sends become our customers' payroll. Before the build reaches this layer, we want the backend and its contract with our platform specified in writing by someone who has done it in production. Looking for an experienced node.js backend developer to deliver a written technical specification of the backend behind the app: the mobile API, offline sync, device sessions, tenant isolation, media upload, push notifications and audit logging, plus the internal API between that backend and our existing platform. No call needed - we want a structured written document our engineers build from and our customers' IT people can read. There is a second reason to do this now. Our larger customers run a security review on every vendor change, and an app that carries job addresses, site photos and staff time records will trigger those reviews. We want the saas developer view on customer data, access control, data retention and logging designed in from the start, not patched after the first security questionnaire arrives. What the written specification should cover: What the new backend owns and what stays in our platform, and how the two integrate - internal API, shared database or something else, and why The mobile API itself - endpoints, versioning, error handling, rate limits, and an API contract our engineers can review before code is written Sign-in on company phones that crews share between shifts or lose - device sessions, token refresh, revoking a device the same day Multi-tenant data isolation - how one customer's data stays invisible to every other customer, through the app as well as the web Offline-first sync - the offline queue, idempotent ingestion, ordering, and what happens when the office and the field change the same job Site photos and signatures - resumable upload on a bad connection, storage, encryption, and who can see them afterwards Push notifications for new and changed jobs, device token lifecycle, and what is allowed to be in a notification Backward compatibility, because phones in the field will not all update at once Audit logging, so we can answer a customer who asks who saw or changed what What a customer security review is likely to ask about this layer and where the answer sits in the design The screens our office will need in the web platform to see sync status and resolve conflicts Hosting, monitoring and alerting for the new service, and a rough build estimate in hours Pitfalls you have seen on backends behind field service or offline-first mobile apps Who we are looking for: a node.js backend developer with production SaaS APIs behind them - Node.js and TypeScript, PostgreSQL, Redis, queues and workers, REST APIs with written contracts - who has built the backend for at least one mobile app that had to work offline. Experience with multi-tenant platforms and with answering customer security questionnaires is a strong plus. Someone who thinks like a full stack developer helps, because part of this is what our office sees on the web side. Format: 6-10 pages, structured, no fluff. Google Doc is fine. Specifics about our platform, our customers, the security questionnaires and the work done on the app so far will be shared only after the contract is signed, under NDA. Access to code and documentation comes after the contract as well. To apply, please share: 2-3 production APIs or SaaS backends you have built, at least one that served a mobile app A short note on how you would handle two people changing the same job when one of them was offline for half a day Your fixed price for the written specification If the specification lands well, this is the first step of a longer engagement - the backend part of the build itself.