Senior Fullstack Engineer (TS, React, Python)

We're building a platform that companies use to create marketplaces that help people find the right kind of provider and book an appointment. Payer and employer partners deliver it to their members inside their own sites and apps, through embeddable experiences, SDKs, an API, and
an MCP server.
You'll build those surfaces and the API behind them. The work spans the embeddable widget clients place on their sites, the preview app that demonstrates it, the questionnaire and booking flows, SDKs, and a remote MCP server.

This is a hands-on, AI-native role: you'll use coding agents and reusable AI skills every day to ship faster without trading away quality or security.
Responsibilities:
- Build the embeddable widget as web components or iframes, with style isolation, Content Security Policy compatibility, a postMessage protocol, and versioning that won't break partner pages.
- Build the questionnaire and booking flows, white-label theming, and the preview app, to WCAG 2.1 AA.
- Implement endpoints in the shared OpenAPI contract, in Python services, including tenancy and partner authentication.
- Generate SDKs from the OpenAPI contract, write developer documentation, and build the sandbox experience for partner developers.
- Ensure proper handling of PHI.
- Write unit, integration, and end-to-end tests, ship through CI/CD, monitor what you build, and support incident response.

Mandatory Skills Description:
- 6+ years of full-stack engineering experience shipping production web applications.
- Experience building embeddable widgets, third-party-hosted web components, or SDKs that run inside other companies' products.
- Strong TypeScript and React, plus backend services in Python (e.g., FastAPI).
- Command of the web platform for embedding: custom elements and Shadow DOM, iframe sandboxing, Content Security Policy, and postMessage.
- REST API design with OpenAPI, including SDK generation from specs. GraphQL experience is a plus.
- Practical knowledge of OAuth 2.0, OpenID Connect, and SSO.
- Experience working with PII and/or PHI under HIPAA.
- Daily use of AI coding tools like Claude Code, with the judgment to keep AI-assisted code correct, tested, and secure.
- You drive work to landed, not merged, and you own the result.