Senior Platform Engineer

Description

Please read first

This is a full-time, in-person role based in San Francisco (Presidio). We work from the office 5 days a week.

You must be based in the Bay Area or willing to relocate before starting.

We require US work authorisation, but are open to O-1 or J-1 visa sponsorship for exceptional candidates.

About Sauna by the company

Every tool you use was built as an island, so you became the glue between them: a name from Gmail into the CRM, a time from the CRM into Calendly, a note from Calendly into a doc. AI showed up and mostly became an eleventh window to paste into.

Sauna is a hybrid of AI and software standing on one shared brain. It holds your context and hands you real software built on top of it, so an ordinary Calendly becomes one that writes the invite itself and knows which of your busy hours bend, and for whom. Software for the path you repeat, AI for the edge that never repeats.

We build from an office in the Presidio, fifty metres from Crissy Field beach, and we work absurdly hard because we can see and feel the outcome every day.

About the Role

Sauna's agent runtime has to keep track of work when a tool fails or new code ships mid-task. One session might start with a message, check Calendar, draft a Slack reply, and update Linear after the first response. A tool call can time out after the action succeeds; the runtime needs to know what happened before retrying.

You'll build the execution engine behind those sessions, choosing when work belongs in an actor and when a job is enough. You'll also design how long-running processes deploy while other tasks are in flight. This is a senior, hands-on engineering role. You'll make those calls with the team, write the code, and own it in production. We'll teach you our agent harness.

Responsibilities

• Build and improve the runtime that starts agent work, carries session state through tool calls, and resumes interrupted runs.
• Choose between actors and jobs for different kinds of work. Implement the choice and check how it behaves when sessions overlap.
• Design how long-running processes drain or resume when code changes, keeping in-flight work accounted for across releases.
• Handle retries and timeouts around tool calls, including cases where an external action succeeded but the response never came back.
• Make runtime failures traceable. Find why a run stopped or stalled, fix the execution path, and see the change through to production.
• Stack: TypeScript, Cloudflare Workers, Durable Objects, Postgres, Docker. Experience with comparable runtimes counts.

Requirements

• Minimum
• You've built and operated stateful backend systems in production, including work that outlasts the request that started it.
• You can explain a decision you made between an actor, a background job, or a simpler service, and show what you shipped.
• You've debugged concurrency, retries, or recovery in code you've owned.
• You're productive in TypeScript and want to keep writing code as your scope grows.
• Bonus
• You've worked on an agent runtime or agent harness.
• You've worked with Cloudflare Workers, Durable Objects, or another actor-based runtime.
• You've deployed long-running processes that persist or resume work across a code release.

Conditions

Base salary: $180K-$240K + meaningful early-stage equity + health, dental, 401(k), considerable PTO, gym budget, lunch.

The Process

We keep our process simple. Exceptional candidates go from first touch to offer within 2 weeks.

Application: Submit your resume and answer a few short questions.

15-minute intro call: Quick check to align on location, motivation, and logistics. If it's a go, we move fast from here.

45-minute technical interview: You'll work through a real backend problem. We're looking for fluency, depth, and how you think about systems.

System design interview: We'll walk through a real the company architecture problem together.

Final conversation: We answer your questions and scope out the work trial.

Work trial: Paid trial to work on a real project in person with us, usually a few days to two weeks. See how we work and whether this feels like the right fit on both sides.

 

Experience: 5+ years

Visa: US citizen/visa only