# ADR-0003: Dependency Injection Framework

## Status
Accepted

## Context
The platform requires dependency injection to:
- Manage service lifecycle
- Wire dependencies between components
- Support module system initialization
- Handle graceful shutdown
- Provide testability through dependency substitution

Options considered:
1. **uber-go/fx** - Runtime dependency injection with lifecycle management
2. **uber-go/dig** - Compile-time dependency injection
3. **Manual constructor injection** - No framework, explicit wiring

## Decision
Use **uber-go/fx** (v1.23.0+) as the dependency injection framework.

**Rationale:**
- Provides lifecycle management (OnStart/OnStop hooks) crucial for services
- Supports module-based architecture through fx.Option composition
- Runtime dependency resolution with compile-time type safety
- Excellent for modular monolith architecture
- Well-documented and actively maintained
- Used by major Go projects (Uber, etc.)

## Consequences

### Positive
- Clean lifecycle management for services
- Easy module composition via fx.Option
- Graceful shutdown handling built-in
- Test-friendly with fx.Options for test overrides

### Negative
- Runtime reflection overhead (minimal)
- Learning curve for developers unfamiliar with fx
- Slightly more complex error messages on dependency resolution failures

### Implementation Notes
- Install: `go get go.uber.org/fx@v1.23.0`
- Create `internal/di/container.go` with fx.New()
- Use fx.Provide() for service registration
- Use fx.Invoke() for initialization tasks
- Leverage fx.Lifecycle for service startup/shutdown