Senior Backend Developer — .NET / PostgreSQL (Healthcare SaaS)

We're building CarePortal — a multi-tenant SaaS platform for UK care home operations: billing, workforce management, and regulatory compliance. The billing engine is ledger-grade: append-only financial records, penny-accurate calculations, tamper-evident audit trails. You'll be the dedicated backend engineer working alongside the founder and an AI-augmented development
workflow on a codebase with strong architectural governance (documented invariants, ADRs, design-locked schema).

What you'll do

- Build and maintain ASP.NET Core APIs (CQRS via MediatR) over PostgreSQL with EF Core
- Implement financial workflows: invoicing, payment allocation, reconciliation, funder ledgers
- Write rigorous tests — unit, integration (Testcontainers/PostgreSQL), BDD (Reqnroll/SpecFlow)
- Own DB migrations, query performance, and data-integrity constraints
- Work within established architecture (layer boundaries, append-only ledger discipline, audit-trail requirements) — and challenge it with evidence when it's wrong
- Collaborate with AI coding agents as part of daily workflow — review, direct, and verify agent-produced code

Must have

- 4-7 years .NET backend (ASP.NET Core, C#, async/await discipline)
- Strong EF Core: migrations, query translation pitfalls, concurrency tokens, performance
- Real PostgreSQL experience (not just SQL Server) — indexes, constraints, triggers
- Testing rigour: you write regression tests that fail before the fix
- Financial-domain or correctness-critical systems experience (billing, payments, ledgers, accounting)
- Self-directed — this is a small team; you own outcomes, not tickets

Nice to have

- MediatR / CQRS patterns; multi-tenant SaaS architecture
- UK healthcare / GDPR / audit-compliance exposure
- Docker, GitHub Actions CI/CD
- Experience working with AI coding tools (Copilot, Claude, Cursor) productively