# System Architecture & Invariants: High-Performance Go & Fiber API Specialist

## 1. System Overview
Production standards for Go Fiber microservices. Enforces explicit error handling, context propagation, and clean layered architecture.
All AI agents operating within this repository must adhere strictly to these architectural boundaries.

### Technology Stack
- **Framework**: Go Fiber v3
- **Language Standard**: Go (Golang 1.22+)
- **UI & Styling**: None / API Service
- **Data Persistence**: PostgreSQL / pgx / Redis
- **Engineering Philosophy**: strict

## 2. Core Architectural Invariants
- **Clean Layered Architecture**: Decouple presentation, business logic, and data access layers via interfaces.
- **Guard Clauses & Early Returns**: Exit early from functions to eliminate deeply nested if-else pyramids.
- **Explicit Result / Tuple Returns**: Return [error, result] or Result<T, E> types for operations that can fail.

## 3. Data Flow & State Management Principles
1. **Unidirectional Data Flow**: State flows top-down; mutations flow through explicit, typed handlers.
2. **Boundary Validation**: External inputs (API payloads, query parameters, environment variables) must be parsed with strict schemas before reaching domain logic.
3. **Surgical Precision**: Diffs must remain minimal and scoped exclusively to the objective. Do not reformat unrelated code.

## 4. Forbidden Anti-Patterns & Operational Guardrails
- **Inspect Before Acting**: Always read and understand existing code and imports before suggesting changes.
- **Minimal Surgical Diffs**: Touch only lines relevant to prompt. Preserve existing comments and formatting.
- **Propose Verification Steps**: With every modification, specify concrete commands or tests to verify correctness.

## 5. Domain-Specific Invariants
- Never call panic() in production request handlers.
- Inject dependencies into struct receivers rather than using package globals.

## 6. Implementation Reference Patterns

### Preferred Pattern
```go
// Good: Explicit error handling with context
func (h *Handler) GetUser(c *fiber.Ctx) error {
    id := c.Params("id")
    user, err := h.service.FindByID(c.UserContext(), id)
    if err != nil {
        if errors.Is(err, domain.ErrNotFound) {
            return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
        }
        return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "internal"})
    }
    return c.JSON(user)
}
```

### Forbidden Anti-Pattern
```go
// Discouraged: Ignored errors and missing context
func GetUser(c *fiber.Ctx) error {
    id := c.Params("id")
    user, _ := db.Find(id)
    return c.JSON(user)
}
```

## 7. Verification Protocol
Before finalizing any implementation:
1. Check all errors explicitly (if err != nil); never discard errors with '_'.
2. Propagate request context (c.UserContext()) to all database and remote calls.
3. Structure application into cmd/, internal/handlers/, internal/services/, and internal/models/.
4. Use Fiber validator middleware to parse and validate request structs.