Senior Backend Engineer (Node.js/Python) for "Zero-UI" API Routing & Stripe Escrow Integration

[Job Title] Senior Backend Engineer (Node.js/Python) for "Zero-UI" API Routing & Stripe Escrow Integration [Project Overview] We are building a highly secure, backend-only "A2A (Agent-to-Agent)" communication protocol. Please note: NO frontend (UI/UX) development is required for this project. The goal of this project is to build an automated backend routing system where two independent nodes can negotiate a schedule via JSON payloads in the background, and immediately trigger a micro-escrow payment lock-up using Stripe API upon agreement. [Core Responsibilities & Features to Build] Hash Mapping System: Convert user identifiers (e.g., phone numbers) into hashed keys to act as communication nodes. A2A Negotiation Logic: Build RESTful API endpoints that allow Node A and Node B to exchange schedule data (Time, Capacity, Deposit limits) via JSON. The system must enforce a maximum "3-ping-pong" rule to reach an agreement or terminate. Micro-Escrow Integration (Stripe): Once both nodes agree on the schedule, automatically trigger a Stripe API call to place a temporary hold (Auth) on a specific amount (e.g., $10) without any frontend UI intervention. Build the logic to either "Capture" (No-show) or "Release" (Visited) the hold based on webhook triggers. [Required Tech Stack] Backend: Node.js (Express/NestJS) or Python (Django/FastAPI) Database: PostgreSQL or MongoDB Payment Gateway: Deep experience with Stripe Connect & Stripe Payment Intents (specifically Auth & Capture flow) Version Control: Git / GitHub [Milestone Payment Structure] We strictly follow a 3-step milestone payment structure to ensure quality and transparency: Milestone 1 (30%): Completion of Node-to-Node JSON communication API and hashing logic. (Successfully demonstrating two servers negotiating a schedule). Milestone 2 (40%): Successful integration of Stripe Escrow (Auth/Hold) logic in the Test Environment. Milestone 3 (30%): Final QA, bug fixing, and 100% transfer of source code and IP rights to our GitHub repository. [Strict Requirements & NDA] All source code and Intellectual Property (IP) developed during this project will belong 100% to the client. You may not use this specific core logic in your public portfolio. To prove you are a human and have read this entirely, please start your proposal with the phrase: "Zero-UI Escrow Protocol". Proposals without this exact phrase will be automatically declined.