Build Historical Market Data API

## Python Backend Developer Needed: Historical Market Data API (FastAPI, WebSockets, Parquet)

We are looking for an experienced **Python backend developer** to build a production-ready historical market-data API for a commercial platform.

### Project Scope

- **REST API:** Dataset discovery, metadata, historical data access, authentication, API keys, customer entitlements, and quotas.
- **Historical downloads:** Efficient delivery of large Parquet datasets stored in S3-compatible object storage.
- **WebSocket replay:** Deterministic historical replay of order-book and trade data, including correct ordering, state reconstruction, gaps, resets, and reconnection handling.
- **Concurrency and performance:** At least 8 simultaneous replay sessions, slow-client isolation, bounded memory, and resource fairness between downloads and replay. Architecture should support future expansion to 16+ sessions.
- **Production readiness:** PostgreSQL, automated tests, logging, monitoring, security, Docker deployment, documentation, and operational handover.

### Required Skills

Python, FastAPI, asyncio, WebSockets, PostgreSQL, Parquet/PyArrow, S3-compatible storage, Docker, and Linux.

Experience with financial market data, streaming systems, or performance-sensitive APIs is a strong advantage.

### Important: Technical Assignment Attached

**Please carefully review the attached ZIP before bidding.**

It includes the complete backend assignment, technical specifications, data contracts, milestones (M1–M6), and mandatory acceptance tests (T01–T22).

We already have detailed technical requirements. We are looking for **implementation and delivery, not an expensive architecture-only consulting phase**.

### Proposal Requirements

Please provide:

1. Your estimated **total cost and delivery timeline for M1–M6**, broken down by milestone.
2. Your hourly rate and weekly availability.
3. Links to substantial backend projects you personally developed or maintained.
4. Your experience with asynchronous programming, WebSockets, and production systems.
5. The main technical risks you identify in our assignment and how you would address them.

We prefer individual freelancers over agencies.

**Please do not submit a generic proposal. We will prioritize candidates who have reviewed the attached assignment and demonstrate strong technical judgment, reliability, and ownership.**