Senior Staff Software Engineer - C#, Agentic Workflows & Native AI Engineering, .Net 8/9, AWS (Lambda, SQS) – OUTSIDE IR35 at Smart Sourcer, United Kingdom, £700-£900 per day

Senior C# Engineer - Agentic Workflows & Native AI Engineering, .Net 8/9, AWS (Lambda, SQS) – OUTSIDE IR35

Reporting to the Director of Engineering, this is a genuinely outstanding contract opportunity for a rockstar Senior C# Engineer to lead the development of a greenfield SaaS product. We’re looking for a ‘best of breed’, deeply senior, technically hands‑on engineer who thrives in complex problem spaces and fast-moving start-up & scale-up environments. You’ll need a genuinely Product Centric mindset and approach twinned with experience of AI‑Native Engineering and Agentic Workflow.

Skills We’re Looking For:

• Senior–Staff‑level backend engineer with deep, current expertise in C# and .NET Core 8/9, capable of architecting and leading the design of distributed REST API microservices at scale.
• Authority in AWS serverless architecture; Lambda‑first, with strong working knowledge of API Gateway, SQS, Step Functions, EventBridge and IAM, and a track record of shipping production workloads on this stack.
• Hands‑on experience with Claude Code (or similar) and advanced agentic workflows; multi‑agent orchestration, context management, custom commands/skills and scaling AI‑assisted delivery across a team.
• Expertise across Aurora RDS MySQL and DynamoDB; schema design, access patterns, indexing, query tuning, single‑table vs multi‑table trade‑offs, and pragmatic thinking around consistency, scaling and cost.
• Proven experience designing event‑driven systems with SQS and adjacent AWS messaging; idempotency, retries, ordering, DLQs and operational robustness.
• Strong API design sensibility; versioning, documentation, throttling, backwards compatibility and a genuine obsession with developer experience.
• A strong product brain; comfortable operating without a traditional Product Owner, partnering with BAs, making sensible trade‑offs, prioritising ruthlessly and owning the solution through to delivery.
• Excellent communication skills and comfort with ad‑hoc client interaction, able to ask the right questions, shape requirements and translate outcomes into shippable work.
• Rigorous engineering standards; Git‑based workflows, trunk‑based development, CI/CD (ideally GitHub Actions), IaC (AWS CDK or Terraform), comprehensive testing and secure‑by‑default coding.
• A pragmatic, outcome‑oriented mindset; comfortable with ambiguity, biased to shipping, and able to make sensible calls on scope, sequencing and technical debt.

What You’ll Own & Deliver:

• Architect, build and ship complex distributed services in C# and .NET Core 8/9, primarily serverless on AWS Lambda, setting the technical bar for the squad and delivering major feature sets end‑to‑end.
• Build resilient, event‑driven systems using SQS and related AWS messaging primitives; idempotency, retries, DLQs, ordering and clean service boundaries.
• Leverage Claude Code, advanced agentic workflows and native AI engineering practices; orchestrating sub‑agents, managing context, running parallel workstreams and embedding AI‑native engineering patterns into everyday delivery.
• Own each feature’s solution end‑to‑end; partnering with BAs on high‑level problems, then driving product thinking, scoping, trade‑offs and delivery yourself.
• Design clean, well‑versioned, well‑documented APIs that other engineers love to consume; treating developer experience and contract stability as first‑class concerns.
• Champion a high‑quality engineering culture; test coverage, peer review, CI/CD discipline (GitHub Actions), IaC, secure coding, observability and performance

£700 - £900 per day. OUTSIDE IR35. 100% remote. 6 months rolling.