Lead Backend / Integrations Engineer (Python, FastAPI, Postgres)

AP US Tax Compliance and Advisory is a US tax firm based in Israel serving Israeli investors with US real estate and US citizens living abroad. Owner-run, growing, and building its own technology.

THE PROJECT
We prepare US tax returns in Wolters Kluwer CCH Axcess and have automated most of the preparation through CCH's REST API: import, calculation, printing, review memos, e-file qualification and release all run from code today. What runs in scripts must become a product before the 2027 filing season: a client platform where clients (or their AI assistants) complete a structured intake, the system extracts data from documents, prepares the return through CCH, routes it to a human reviewer and signer, collects an e-signature and payment, releases the e-file and delivers the result. The design document, data model, state machine, API and security model are written. You will be the first engineer and you will own the backend.

RESPONSIBILITIES
- Backend architecture and implementation: Python 3.12, FastAPI, SQLAlchemy/Alembic, Postgres, a job queue, workers, webhooks.
- The CCH Axcess API module as a server-side job runner: one in-flight job per return, global concurrency limits, exponential backoff on locks, idempotency keys, prompt handling, structured results, parked-job alerts.
- Security engineering: PII vault with field-level encryption (KMS), tokenized payload assembly, append-only audit log, RBAC with step-up MFA for sensitive actions, PII-free logging with a redaction layer, secrets manager, backups and restore tests.
- Integrations: Stripe (payments, webhooks), an e-signature vendor with identity verification, Google Drive, transactional email, WhatsApp Business API, Anthropic API for document extraction with human confirmation.
- Infrastructure as code on AWS (ECS Fargate or App Runner, RDS, S3, KMS, Secrets Manager, CloudWatch) or an agreed managed platform; CI with tests and security scans; staging and production environments; runbooks.
- You work against a mock CCH server built from our specification; production runs are performed by the firm. You will never hold production credentials or see client data.
- Collaboration: a full-stack engineer on the portal and staff console; an AI assistant that writes specifications and reviews every pull request before the owner sees it; a weekly 30-minute call with the owner.
- After the build: a retained maintenance agreement including on-call during the filing season.

REQUIREMENTS
- 5+ years building Python backends in production, 2+ years as the person responsible for a system's reliability.
- Deep Postgres: schema design, migrations, transactions, indexing, point-in-time recovery.
- Integrations with unreliable third-party APIs: retries, idempotency, partial failure, long-running jobs with polling.
- Security habits: least privilege, secrets management, no sensitive data in logs, dependency hygiene. You can explain how you would design a system where the people who build it never see the data it holds.
- Docker; one major cloud; infrastructure as code.
- Clear written English; you document decisions and write runbooks without being asked.
- At least four hours of daily overlap with Israel (UTC+2); availability December 2026 through June 2027 at 30-40 hours per week.

NICE TO HAVE
- Fintech, payments, accounting, insurance or health-data experience; SOC 2 or ISO 27001 exposure.
- LLM API experience (Anthropic/OpenAI SDKs, tool use, structured outputs) or MCP servers.
- Experience with XML-heavy enterprise APIs.
- Russian or Hebrew (the owner speaks both; not required).

ENGAGEMENT TERMS
- Independent contractor (B2B) via Deel, Payoneer or Upwork; NDA, IP assignment and the firm's confidentiality agreement signed before access to any repository.
- Phase 1: December 1, 2026 to April 30, 2027, 30-40 h/week; USD 3,500-6,000 per month (or USD 30-45/h) depending on seniority and hours.
- Phase 2: May 2027 onward, retained maintenance 10-20 h/week plus on-call in season, priced separately.
- Access: development and staging only; no production data, no production credentials; mock CCH server and synthetic data.
- Remote; Ukraine, Poland, Georgia, Armenia, Serbia, Kazakhstan and similar time zones preferred. Not available to contractors located in Russia.

PROCESS
1. Written application with three short answers: (a) one third-party API integration you built that had to survive locks, rate limits or inconsistent responses, and what you did about it; (b) how you keep secrets and personal data out of logs in a system you run; (c) your availability December 2026 to June 2027 and your overlap with UTC+2.
2. 30-minute call with the owner.
3. Paid trial task: 10-15 hours over one week, USD 500 paid regardless of outcome, on the mock server with synthetic data.
4. References, contract, onboarding. Target start: December 1, 2026.

Apply with a CV or LinkedIn profile, links to code or systems you are proud of, and the three answers. Applications without the answers are not reviewed.