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HarperHarperSan Francisco, CA

Staff Engineer, Harness Engineering

As a Staff Engineer, Harness Engineering, you will own the meta-harness that powers all Harper AI agents, both product and coding. This involves designing and building the agent loop, execution environment, tool layer, and model-provider abstraction to ensure efficient and reliable agent operation.

253k – 308k
On-site8+ YOEML Engineering

About the role

The Role

Harper operates like a factory with a series of modules spanning the full lifecycle from intake through renewals. Across them we run a stack of internal AI systems covering operator guidance, the operational backbone that matches risks to underwriters, autonomous communications, and voice AI for customer interactions.

Underneath all of that lives the harness substrate you'll own - the meta-harness wrapping our frontier coding agents, OpenClaw, Hermes, and the model-routing layer on top of our foundation-model providers. You define the contracts every Harper agent integrates against.

What You'll Own

  • The agent loop - Prompt construction, tool routing, context-window management, retry/timeout/budget logic, multi-step orchestration
  • Execution environment - Sandbox lifecycle, isolation, blast-radius limits, file-system + network policy for agents that browse or call APIs
  • Tool layer - The canonical set of tools every agent can call. Schema, auth, rate-limit, observability per tool.
  • Model-provider abstraction - Provider routing, fallback chains, cost/latency tradeoffs, eval-driven model selection
  • Multi-agent coordination patterns - Parent/child handoff, shared memory contracts, parallel execution, conflict resolution, subagent budgets
  • The harness SDK - What every pod engineer imports when they ship an agent. If pod engineers ship faster, you did this right.
  • Guardrails - Banned tool combinations, prompt-injection defense, data-egress policy, PII scrubbing

You Might Be a Fit If…

  • You've built or owned an agent harness at an AI-substrate company (or a strong open-source equivalent)
  • You can describe trade-offs between agent loops you've used and have opinions on which works when
  • You think in tool design, not just prompt design - the prompt is the last 5%, the tool surface is the work
  • You've shipped sandbox infrastructure at scale (Firecracker, gVisor, comparable isolation)
  • You write code with AI daily and have strong opinions about which harness behaviors matter and which are theater
  • You're 8–12 years into your career with 3+ years at the Senior+ level

Requirements

  • 8+ years software engineering experience, including senior+ scope at a high-growth company
  • Production agent-harness or AI-substrate experience - agent loop, tool routing, execution environment, model routing
  • Strong written communication - RFCs, API contracts, integration guides
  • Based in San Francisco or willing to relocate

Nice to Have

  • Open-source contribution to agent/harness frameworks
  • Sandbox/isolation infrastructure depth
  • Foundation-model partner or early-access experience

Compensation

OTE: $253,000–$308,000 cash compensation (base salary + target performance bonus) Equity: competitive equity, so you share in the company you are helping build Location: San Francisco, in-office

Benefits

  • Health, dental, and vision insurance
  • Commuter benefits
  • Team meals and snacks

Skills

AIAgent HarnessSandbox InfrastructureModel RoutingAPI DesignSystem DesignSoftware EngineeringFirecrackerGvisor

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