FastAPI

# MISSION: Scaffold "FastAPI" Production Architecture
You are an expert Senior Staff Software Architect and Full-Stack Engineer. Your mission is to scaffold and implement a production-grade, highly reliable, and modular codebase following the proven architecture of **FastAPI**.
---
## 1. PROJECT SPECIFICATIONS & BENCHMARK
- **Reference Architecture**: FastAPI
- **What It Does**: FastAPI is a Python web framework that generates request validation, serialization and an interactive OpenAPI/Swagger UI/ReDoc documentation site directly from type-hinted routes and Pydantic models, built on top of the Starlette ASGI toolkit.
- **Domain & Category**: High-Performance Python Web API Framework
- **Production Scale**: 1M+ MAU
- **Development Mode**: CLASSIC
- **Architectural Rationale**: FastAPI keeps its own dependency surface to Starlette and Pydantic and pushes servers, CLI, templating, forms and settings into an optional 'standard' extra, so a bare install stays minimal while typical apps opt into one bundle instead of assembling it dependency by dependency.
- **Live Website Reference**: https://fastapi.tiangolo.com
- **Source Repository**: https://github.com/fastapi/fastapi
---
## 2. PRODUCTION TECH STACK
- **Full Stack Array**: Python, Starlette, Pydantic, Uvicorn, uv, pytest, mypy, Ruff, GitHub Actions
- **Primary Language(s)**: Python
- **License of the reference repo**: MIT
- **Frontend**: Swagger UI — Interactive API docs generated from the OpenAPI schema; configurable via fastapi/openapi and docs_src/configure_swagger_ui.; ReDoc — Second interactive docs UI generated from the same OpenAPI schema, shown alongside or instead of Swagger UI.
- **Backend & APIs**: Starlette — ASGI toolkit FastAPI builds routing, middleware, WebSockets and request/response handling on top of.; Pydantic — Validates and serializes request/response data from Python type hints (pydantic>=2.9.0 required).; Uvicorn — ASGI server used by `fastapi dev`/`fastapi run`; installed via the optional 'standard' extra (uvicorn[standard]).
- **Infrastructure & deploy**: uv — Documented install/run tool for FastAPI apps (`uv add "fastapi[standard]"`, `uv run fastapi dev`) per the README quick start.; pytest — Test runner (pytest>=9.0.0) with strict-config, strict-markers and a 20s per-test timeout.; mypy — Strict type checking (`strict = true`) across the codebase via the pydantic.mypy plugin.; Ruff — Lints pyflakes/pycodestyle/isort/bugbear/comprehension/pyupgrade rules (E, W, F, I, B, C4, UP).; GitHub Actions — Runs the test suite, docs build/deploy, pre-commit hook bumps, translation automation and release drafts (20 workflows).
- **Tooling, testing & ops**: Pydantic AI — Included in the translations dependency group to assist the docs translation pipeline behind translate.yml.
---
## 3. KEY ARCHITECTURAL DECISIONS (audited from https://github.com/fastapi/fastapi @ 50113da)
1. **Built directly on Starlette and Pydantic, not a custom core**: pyproject.toml's runtime `dependencies` list is just starlette>=0.46.0, pydantic>=2.9.0, typing-extensions, typing-inspection and annotated-doc; FastAPI's routing/ASGI layer is Starlette's, and all validation/serialization is Pydantic's, rather than FastAPI reimplementing either.
2. **Almost every feature is opt-in through the "standard" extra**: [project.optional-dependencies].standard in pyproject.toml pulls in fastapi-cli, httpx, jinja2, python-multipart, email-validator, uvicorn[standard], pydantic-settings and pydantic-extra-types; installing bare `fastapi` with no extras gives none of the CLI, templating, forms, or dev server.
3. **Two docs UIs are generated from one OpenAPI schema, not hand-written pages**: fastapi/openapi builds the OpenAPI schema from route type hints and Pydantic models; docs_src/configure_swagger_ui and docs_src/custom_docs_ui show both Swagger UI and ReDoc being served, restyled, or swapped out from that same generated schema.
4. **Strict mypy runs alongside a second, independent type checker**: [tool.mypy] sets strict = true with the pydantic.mypy plugin, and the `tests` dependency group additionally pins `ty>=0.0.25` (Astral’s Rust type checker), so the same codebase is checked by two independently implemented type checkers rather than one.
5. **Performance regressions are benchmarked in CI, not just caught by tests**: The `tests` dependency group includes pytest-codspeed>=4.3.0, and tests/benchmarks plus tests/memory_benchmarks are separate directories explicitly excluded from coverage reporting in [tool.coverage.run].omit, keeping benchmark runs distinct from correctness tests.
6. **Docs translation has a dedicated automation dependency group**: A `translations` group in [dependency-groups] (gitpython, pydantic-ai, pygithub) backs the translate.yml and notify-translations.yml workflows listed under .github/workflows, rather than translations flowing through the same review path as code PRs.
7. **The documentation build pipeline spans two static-site generators**: The `docs` dependency group installs both zensical>=0.0.42 and mkdocstrings[python]>=1.0.3 (plus griffe-typingdoc and griffe-warnings-deprecated) to build the docs_src tutorials that are translated into 15+ language folders under docs/.
---
## 4. NON-NEGOTIABLE ARCHITECTURAL GUARDRAILS
1. **Monorepo & Modular Separation**:
   - Structure as a Turborepo monorepo with strict package boundaries:
     - `apps/web`: Application UI, routing, layouts, and server endpoints.
     - `packages/ui`: Shared design tokens, CSS variables, and Radix UI primitive components.
     - `packages/db`: Database schemas, client singleton, declarative migrations, and seed scripts.
     - `packages/config`: Shared TypeScript, ESLint, and build configurations.
2. **Strict Type Safety & Zero `any` Policy**:
   - Enable `strict: true`, `noImplicitAny: true`, and `strictNullChecks: true`.
   - Validate ALL external inputs, API request bodies, and query parameters with **Zod** schemas before execution.
3. **Frontend & Rendering Guidelines**:
   - Isolate interactive UI state to leaf components. Keep core pages lightweight and performant.
4. **Design System & Aesthetics**:
   - Keep every color, radius, shadow and font in a single token file (CSS variables) and consume tokens everywhere; never hardcode hex values in components.
   - Prefer crisp 1px borders and one subtle shadow scale over blurry default shadows. Pair one sans-serif for body/headings with one monospace for tags, badges, metrics, and code.
5. **Data Layer & Reliability**:
   - Write declarative schema definitions with foreign keys, composite indexes on queried filters, and automated timestamp triggers.
   - Use connection pooling and prepared statements for serverless database execution.
---
## 5. STEP-BY-STEP SCAFFOLDING ROADMAP
- **Phase 1: Workspace & Root Config**: Initialize package manager, monorepo configuration (`turbo.json`, `tsconfig.base.json`, `package.json`).
- **Phase 2: Database Schema & Client**: Set up the data layer: client, connection pool, models, and migration scripts.
- **Phase 3: Design Tokens & UI Primitives**: Build accessible `Button`, `Input`, `Card`, `Badge`, and layout wrappers inside `packages/ui`.
- **Phase 4: Core Application Routes & Handlers**: Implement primary authentication, user session handling, and application routes.
- **Phase 5: Quality Assurance & Build Verification**: Run `tsc --noEmit`, ESLint, Prettier, and smoke test suites to ensure zero compilation or runtime errors.
---
## 6. EXECUTION INSTRUCTIONS
1. Review all specifications, architectural guardrails, and stack choices above.
2. Present the full monorepo directory tree structure.
3. Systematically generate the complete, production-ready codebase according to the 5-phase roadmap above — starting with the root workspace setup, followed by the database schema, UI design system package, and full-stack application routes until the repository is fully scaffolded and ready to run.