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docs/content/stories/epic0/0.2-configuration-management-system.md

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+# Story 0.2: Configuration Management System
+
+## Metadata
+- **Story ID**: 0.2
+- **Title**: Configuration Management System
+- **Epic**: 0 - Project Setup & Foundation
+- **Status**: Pending
+- **Priority**: High
+- **Estimated Time**: 4-6 hours
+- **Dependencies**: 0.1
+
+## Goal
+Implement a flexible configuration system that loads settings from YAML files, environment variables, and supports type-safe access. The system must be injectable via DI and usable by all modules.
+
+## Description
+This story implements a complete configuration management system using Viper that provides a clean interface for accessing configuration values. The system supports multiple configuration sources (YAML files, environment variables) with proper precedence and type-safe accessors.
+
+## Deliverables
+
+### 1. Configuration Interface (`pkg/config/config.go`)
+Define `ConfigProvider` interface with:
+- `Get(key string) any` - Get any value
+- `Unmarshal(v any) error` - Unmarshal into struct
+- `GetString(key string) string` - Type-safe string getter
+- `GetInt(key string) int` - Type-safe int getter
+- `GetBool(key string) bool` - Type-safe bool getter
+- `GetStringSlice(key string) []string` - Type-safe slice getter
+- `GetDuration(key string) time.Duration` - Type-safe duration getter
+- `IsSet(key string) bool` - Check if key exists
+
+### 2. Viper Implementation (`internal/config/config.go`)
+Implement `ConfigProvider` using Viper:
+- Load `config/default.yaml` as baseline
+- Merge environment-specific YAML files (development/production)
+- Apply environment variable overrides (uppercase with underscores)
+- Support nested configuration keys (dot notation)
+- Provide all type-safe getters
+- Support unmarshaling into structs
+- Handle configuration validation errors
+
+### 3. Configuration Loader (`internal/config/loader.go`)
+- `LoadConfig(env string) (ConfigProvider, error)` function
+- Environment detection (development/production)
+- Configuration file discovery
+- Validation of required configuration keys
+- Error handling and reporting
+
+### 4. Configuration Files
+Create configuration files:
+
+**`config/default.yaml`** - Base configuration:
+```yaml
+environment: development
+server:
+  port: 8080
+  host: "0.0.0.0"
+  read_timeout: 30s
+  write_timeout: 30s
+database:
+  driver: "postgres"
+  dsn: ""
+  max_connections: 25
+  max_idle_connections: 5
+logging:
+  level: "info"
+  format: "json"
+  output: "stdout"
+```
+
+**`config/development.yaml`** - Development overrides:
+```yaml
+environment: development
+logging:
+  level: "debug"
+  format: "console"
+```
+
+**`config/production.yaml`** - Production overrides:
+```yaml
+environment: production
+logging:
+  level: "warn"
+  format: "json"
+```
+
+### 5. DI Integration
+- Provider function for ConfigProvider
+- Register in DI container
+- Make configurable via FX
+
+## Implementation Steps
+
+1. **Install Dependencies**
+   ```bash
+   go get github.com/spf13/viper@v1.18.0
+   go get github.com/spf13/cobra@v1.8.0
+   ```
+
+2. **Create Configuration Interface**
+   - Define `ConfigProvider` interface in `pkg/config/config.go`
+   - Add package documentation
+   - Export interface for use by modules
+
+3. **Implement Viper Configuration**
+   - Create `internal/config/config.go`
+   - Implement all interface methods
+   - Handle configuration loading and merging
+   - Support nested keys and environment variables
+
+4. **Create Configuration Loader**
+   - Implement `LoadConfig()` function
+   - Add environment detection logic
+   - Add validation logic
+   - Handle errors gracefully
+
+5. **Create Configuration Files**
+   - Create `config/default.yaml` with base configuration
+   - Create `config/development.yaml` with dev overrides
+   - Create `config/production.yaml` with prod overrides
+   - Ensure proper YAML structure
+
+6. **Integrate with DI**
+   - Create provider function
+   - Register in DI container
+   - Test injection
+
+## Acceptance Criteria
+- [ ] `ConfigProvider` interface is defined and documented
+- [ ] Viper implementation loads YAML files successfully
+- [ ] Environment variables override YAML values
+- [ ] Type-safe getters work correctly (string, int, bool, etc.)
+- [ ] Configuration can be unmarshaled into structs
+- [ ] Nested keys work with dot notation
+- [ ] Configuration system is injectable via DI container
+- [ ] All modules can access configuration through interface
+- [ ] Configuration validation works
+- [ ] Error handling is comprehensive
+
+## Related ADRs
+- [ADR-0004: Configuration Management](../../adr/0004-configuration-management.md)
+
+## Implementation Notes
+- Use Viper's automatic environment variable support (uppercase with underscores)
+- Support both single-level and nested configuration keys
+- Consider adding configuration schema validation in future
+- Environment variable format: `SERVER_PORT`, `DATABASE_DSN`, etc.
+- Configuration files should be in YAML for readability
+- Support secret manager integration placeholder (Epic 6)
+
+## Testing
+```bash
+# Test configuration loading
+go test ./internal/config/...
+
+# Test type-safe getters
+go run -c "test config getters"
+
+# Test environment variable overrides
+export SERVER_PORT=9090
+go run cmd/platform/main.go
+```
+
+## Files to Create/Modify
+- `pkg/config/config.go` - Configuration interface
+- `internal/config/config.go` - Viper implementation
+- `internal/config/loader.go` - Configuration loader
+- `config/default.yaml` - Base configuration
+- `config/development.yaml` - Development configuration
+- `config/production.yaml` - Production configuration
+- `internal/di/providers.go` - Add config provider
+