📝 Add PRD.md and ROADMAP.md documentation

- Add Product Requirements Document (PRD.md) with P0-P3 user stories
- Add Roadmap.md with future ideas and lessons learned
- Add .specify/memory/constitution.md with FastAPI principles

Co-Authored-By: Claude Opus 4.6 <[email protected]>

.specify/memory/constitution.md

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+<!--
+Sync Impact Report:
+- Version change: N/A → 1.0.0 (initial creation)
+- New constitution - no prior version
+- Added sections: 5 core principles, 2 additional sections, governance
+- Templates requiring updates: N/A - this is the initial version
+-->
+
+# FastAPI Constitution
+
+## Core Principles
+
+### I. Standards-Based
+
+FastAPI MUST be built on open standards for APIs. All features MUST support OpenAPI (formerly Swagger) and JSON Schema. The framework MUST generate compliant API documentation automatically. Rationale: Ensures interoperability and automatic tooling support (client generation, documentation).
+
+### II. Type Safety (NON-NEGOTIABLE)
+
+FastAPI MUST leverage Python type hints for request validation, response serialization, and automatic documentation. Type checking MUST pass with mypy at strict level. Rationale: Catches bugs at development time, enables IDE autocomplete, powers automatic documentation.
+
+### III. Test-First Development
+
+All new features MUST have tests written before implementation. The framework MUST maintain comprehensive test coverage. Tests MUST verify both functionality and API contract compliance. Rationale: FastAPI is a framework used in production by millions; regressions are costly.
+
+### IV. Performance
+
+FastAPI MUST achieve performance comparable to NodeJS and Go frameworks. Async support MUST be first-class with no performance penalty for sync code paths. Rationale: Performance is a primary feature claim; benchmarks MUST remain competitive.
+
+### V. Developer Experience
+
+The framework MUST provide intuitive APIs with minimal boilerplate. Error messages MUST be clear and actionable. Documentation MUST include runnable examples. Rationale: "Fast to code" is a core value proposition; reduces developer cognitive load.
+
+## Additional Constraints
+
+### Technology Stack
+
+- **Language**: Python 3.8+ (subject to Python release support policy)
+- **Core Dependencies**: Starlette for routing, Pydantic for data validation
+- **Async**: First-class support for asyncio
+- **Standards**: OpenAPI 3.0+, JSON Schema
+
+### Compatibility
+
+- **Python Versions**: Support Python versions according to PEP 594
+- **Breaking Changes**: Follow semantic versioning; MAJOR version bumps require deprecation warnings in prior minor releases
+- **Dependencies**: Pin minimal required versions; allow compatible updates
+
+## Development Workflow
+
+### Code Quality Gates
+
+- All PRs MUST pass type checking (mypy --strict)
+- All PRs MUST maintain or increase test coverage
+- All PRs MUST include documentation for new features
+- All PRs MUST pass CI/CD pipeline (lint, test, coverage)
+
+### Contribution Process
+
+1. Fork and create feature branch
+2. Write tests first (must fail)
+3. Implement feature
+4. Ensure tests pass and coverage maintained
+5. Update documentation
+6. Submit PR with description
+
+### Release Process
+
+- Follow semantic versioning strictly
+- Maintain changelog
+- Publish release notes
+- Ensure backwards compatibility within MAJOR version
+
+## Governance
+
+The FastAPI Constitution supersedes all other development practices. Amendments to this constitution MUST be documented with:
+
+1. Rationale for the change
+2. Impact assessment on existing workflows
+3. Migration plan if applicable
+
+All PRs and code reviews MUST verify compliance with these principles. Complexity MUST be justified against simpler alternatives.
+
+**Version**: 1.0.0 | **Ratified**: 2026-02-23 | **Last Amended**: 2026-02-23

docs/PRD.md

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+# PRD: FastAPI Framework
+
+FastAPI is a modern, high-performance Python web framework for building APIs with Python type hints. This document outlines the product requirements for the FastAPI framework itself.
+
+## Implementation Status
+
+The core framework is mature and well-established. This PRD tracks major feature initiatives and improvements beyond the stable release.
+
+## User Stories
+
+### P0: Core Framework (Must Have) — ✅ Complete
+
+**As a** Python developer,
+**I want** to build APIs quickly using type hints,
+**So that** I get automatic validation, documentation, and IDE support.
+
+- [P0-US1] ✅ Route definition via decorators with path parameters
+- [P0-US2] ✅ Query, header, and cookie parameter extraction with type hints
+- [P0-US3] ✅ Request body validation using Pydantic models
+- [P0-US4] ✅ Automatic OpenAPI schema generation
+- [P0-US5] ✅ Interactive API documentation (Swagger UI + ReDoc)
+- [P0-US6] ✅ Dependency injection system
+- [P0-US7] ✅ Error handling with custom exception handlers
+- [P0-US8] ✅ Response model typing with automatic serialization
+
+**Acceptance Criteria:**
+- All core HTTP methods supported (GET, POST, PUT, DELETE, PATCH, OPTIONS)
+- Type hints enable validation and documentation without boilerplate
+- OpenAPI 3.0+ compliant schema generation
+
+### P1: Async & Performance (Must Have) — ✅ Complete
+
+**As a** developer building high-throughput APIs,
+**I want** first-class async support,
+**So that** I can handle many concurrent connections efficiently.
+
+- [P1-US1] ✅ Async route handlers with `async def`
+- [P1-US2] ✅ Background tasks for deferred processing
+- [P1-US3] ✅ WebSocket support for real-time communication
+- [P1-US4] ✅ Middleware stack (request/response processing)
+- [P1-US5] ✅ Sub-application mounting for modular apps
+
+**Acceptance Criteria:**
+- Async handlers perform comparably to Node.js/Go
+- WebSocket connections maintained efficiently
+- Middleware applies correctly to all routes
+
+### P1: Security & Authentication (Should Have) — ✅ Complete
+
+**As a** developer building secure APIs,
+**I want** built-in authentication and authorization,
+**So that** I don't have to implement common patterns from scratch.
+
+- [P1-US6] ✅ OAuth2 password flow implementation
+- [P1-US7] ✅ JWT token support
+- [P1-US8] ✅ CORS middleware
+- [P1-US9] ✅ HTTP Basic Auth
+- [P1-US10] ✅ Dependency-based authorization scopes
+
+**Acceptance Criteria:**
+- OAuth2 with JWT tokens works out of the box
+- Security schemes documented in OpenAPI spec
+
+### P2: Developer Experience (Should Have) — ✅ Complete
+
+**As a** FastAPI user,
+**I want** excellent tooling and error messages,
+**So that** I can develop quickly and debug easily.
+
+- [P2-US1] ✅ FastAPI CLI for running and generating projects
+- [P2-US2] ✅ Clear validation error messages with field locations
+- [P2-US3] ✅ Static type checking support with mypy
+- [P2-US4] ✅ Response model documentation in OpenAPI
+
+**Acceptance Criteria:**
+- CLI provides `fastapi dev` and `fastapi run`
+- Error responses include details for each validation failure
+- Type hints work with pyright/mypy
+
+### P2: Extensibility (Should Have) — ✅ Complete
+
+**As a** framework contributor,
+**I want** to extend FastAPI without modifying core code,
+**So that** I can add custom behaviors.
+
+- [P2-US5] ✅ Custom response classes
+- [P2-US6] ✅ Custom parameter types
+- [P2-US7] ✅ Custom middleware interfaces
+- [P2-US8] ✅ OpenAPI extension hooks
+
+**Acceptance Criteria:**
+- Extensions integrate seamlessly with FastAPI
+- Custom components documented in OpenAPI
+
+### P3: Advanced Features (Could Have) — ✅ Complete
+
+**As an** advanced user,
+**I want** sophisticated deployment options,
+**So that** I can optimize for production.
+
+- [P3-US1] ✅ Testing utilities with TestClient
+- [P3-US2] ✅ Dependency overrides for testing
+- [P3-US3] ✅ ASGI server integration (Uvicorn, Hypercorn)
+- [P3-US4] ✅ Gunicorn worker support
+- [P3-US5] ✅ Docker integration and multi-stage builds
+
+**Acceptance Criteria:**
+- Testing patterns documented and working
+- Production deployment guides available
+
+## Architecture: Starlette + Pydantic
+
+FastAPI builds on two key libraries:
+
+| Component | Role |
+|-----------|------|
+| Starlette | Routing, middleware, ASGI handler |
+| Pydantic | Data validation, serialization, OpenAPI generation |
+
+### Request/Response Flow
+
+```
+Request → ASGI Handler → Middleware → Route Handler → Dependency Injection
+                                                        ↓
+Response ← Serialization ← Pydantic Model ← Return Value
+```
+
+### Key Components
+
+| Component | File | Role |
+|-----------|------|------|
+| FastAPI app | `fastapi/applications.py` | Main application class |
+| Routing | `fastapi/routing.py` | Route resolution, OpenAPI generation |
+| Dependencies | `fastapi/dependencies.py` | Dependency injection system |
+| Params | `fastapi/params.py` | Parameter definitions |
+| Response | `fastapi/response.py` | Response handling |
+| OpenAPI | `fastapi/openapi/` | Schema generation |
+
+## Non-Functional Requirements
+
+### Performance
+- Request/response latency comparable to Node.js and Go
+- Minimal overhead for sync handlers
+- Efficient async task scheduling
+
+### Compatibility
+- Python 3.8+ (subject to PEP 594)
+- OpenAPI 3.0+ and JSON Schema
+- ASGI specification compliance
+
+### Security
+- Input validation via Pydantic
+- Secure defaults for authentication
+- No sensitive data in error messages
+
+### Reliability
+- Comprehensive test coverage
+- Deprecation warnings for breaking changes
+- Stable API surface within major versions
+
+## Test Scenarios
+
+1. **Basic API**: Create endpoint, verify request/response
+2. **Validation**: Send invalid data, verify 422 error with details
+3. **Async**: Test async handler with concurrent requests
+4. **Dependencies**: Verify dependency injection ordering
+5. **Auth**: Test OAuth2 flow end-to-end
+6. **Documentation**: Verify OpenAPI schema accuracy
+7. **Middleware**: Test request/response modification
+8. **Sub-app**: Mount app, verify routing isolation

docs/ROADMAP.md

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+# Roadmap
+
+Future enhancements and improvements for the FastAPI framework.
+
+## Completed
+
+All P0–P3 user stories from the original PRD are implemented. See [PRD.md](PRD.md) for details.
+
+Key milestones achieved:
+- Core routing with type hints and automatic validation
+- Async support with first-class performance
+- OAuth2, JWT, and security utilities
+- FastAPI CLI and developer tooling
+- Extensibility via custom components
+- Comprehensive testing utilities
+- Production deployment options
+
+## Ideas (Unprioritized)
+
+These are potential directions. None have user stories or acceptance criteria yet — they need to be scoped before work begins.
+
+- **Improved Error Messages**: More helpful validation errors with suggestions
+- **Typed Middleware**: Type-safe middleware definitions
+- **Enhanced OpenAPI**: More detailed schema generation options
+- **Plugin System**: Formal extension mechanism for third-party integrations
+- **Native gRPC Support**: gRPC reflection and transcoding
+- **GraphQL Integration**: More mature GraphQL schema generation
+- **Better Type Inference**: Improved type hints for complex scenarios
+- **Streaming Responses**: Native support for Server-Sent Events
+- **HTTP/2 Support**: Push promises and header compression
+- **Zero-Config Deployments**: Simplified production setup
+
+## Won't Have
+
+- **Built-in Database ORM**: Users should choose their own (SQLAlchemy, Prisma, etc.)
+- **Built-in Authentication Provider**: Identity management is outside framework scope
+- **Template Engine**: Use external libraries (Jinja2, etc.) directly
+- **Full-Stack Framework**: FastAPI remains focused on APIs only
+
+## Lessons Learned
+
+From years of maintaining FastAPI as a community-driven framework:
+
+1. **Good**: Type hints provide excellent developer experience and IDE support
+2. **Good**: OpenAPI integration enables rich ecosystem (clients, docs, testing)
+3. **Good**: Dependency injection promotes loose coupling and testability
+4. **Issue**: Balancing new features with stability is challenging
+5. **Fix**: Semantic versioning with clear deprecation paths
+6. **Fix**: Comprehensive documentation with examples