Principal Full-Stack Engineer – Diagnose & Stabilize a Distributed Next.js / NestJS Application

We are looking for a Principal-Level Full-Stack Engineer to investigate and stabilize a partially implemented production-grade web application built with Next.js, React, TypeScript, NestJS, PostgreSQL, and Docker This is not a basic bug-fixing task. We need an engineer who can reason across the entire application architecture, identify root causes rather than patch symptoms, and recommend technically sound solutions. Scope of Work The application currently has intermittent issues involving frontend state, backend APIs, database interactions, and asynchronous data flows. Your responsibility will be to perform a focused technical investigation and implement the most critical fixes. Key Areas to Investigate * Analyze the existing Next.js App Router architecture and identify problematic server/client boundaries. * Trace API requests from the React frontend through NestJS controllers/services into PostgreSQL. * Investigate inconsistent or stale frontend state after mutations. * Review asynchronous operations and identify potential race conditions. * Analyze backend error handling and determine why certain failures are being silently swallowed. * Review PostgreSQL queries and ORM interactions for obvious performance or consistency problems. * Identify potential issues with transactions and concurrent updates. * Review Docker configuration and ensure frontend/backend services communicate reliably. * Examine authentication/session handling where relevant. * Identify architectural weaknesses that could become production issues. Principal-Level Requirement We are specifically looking for someone capable of answering: 1. **What is actually causing the problem?** 2. **Why does the current architecture allow the problem to occur?** 3. **What is the safest production-ready fix?** 4. **Could the fix introduce regressions elsewhere?** 5. **How should the architecture be improved to prevent the issue from returning?** Simply modifying code until the error disappears will not be considered sufficient. Deliverables The selected developer should provide: * Root-cause analysis of the identified issues. * Implementation of the highest-priority fixes. * Clean, maintainable TypeScript code. * Appropriate validation/error handling. * Any required database/query improvements. * Updated configuration where necessary. * A concise technical summary explaining: * Issues discovered * Root causes * Changes made * Architectural risks identified * Recommended next steps Technical Environment Frontend * Next.js * React * TypeScript * App Router * REST API integration Backend * Node.js * NestJS * TypeScript * REST APIs Database * PostgreSQL * ORM-based data access **Infrastructure** * Docker / Docker Compose * Linux-based deployment environment Ideal Candidate You should have strong experience with: * Principal/Staff-level software engineering * Distributed application debugging * Next.js and React architecture * NestJS / Node.js backend systems * PostgreSQL * TypeScript * API design * Concurrency and asynchronous workflows * Production debugging * Docker * System architecture and technical decision-making You should be comfortable entering an unfamiliar codebase, understanding it quickly, and making decisions based on system behavior rather than assumptions.