Implement outbox pattern for reliable event publishing in Products microservice

[Copilot]

This PR implements the outbox pattern to ensure reliable event publishing when products are created or updated, addressing the critical requirement for guaranteed event propagation in the Products microservice.

Problem

Previously, product events were published directly to the message broker after database operations, creating a risk of lost events if the message broker was unavailable or if failures occurred between database commits and message publishing.

Solution

Implemented the outbox pattern with the following components:

🗃️ Database Changes

• Added OutboxMessages table to store pending events atomically with product operations
• Includes retry logic, error tracking, and processing timestamps
• Optimized with indexes for efficient background processing

🔄 Core Components

• OutboxProcessor: Processes pending messages and publishes to message broker
• OutboxBackgroundService: Runs every 10 seconds to process pending events
• Enhanced ProductsWriteStore: Atomic operations ensuring product changes and event storage happen in the same transaction

📝 Updated Use Cases

• CreateProductDetails: Now stores events in outbox instead of direct publishing
• UpdateProductDetails: Same transactional approach for update events

✅ Testing

• 7 comprehensive unit tests covering all outbox functionality
• Integration tests verifying end-to-end use case behavior
• All existing tests continue to pass

Benefits

• 🛡️ Guaranteed Delivery: Events are persisted before any external operations
• 🔄 Retry Logic: Failed messages are retried with exponential backoff (max 3 attempts)
• ⚡ Performance: Background processing doesn't block API responses
• 🔍 Observability: Failed messages are logged with error details
• 🔒 Consistency: Database and message broker state remain synchronized

Example Usage

The API contracts remain unchanged - the outbox pattern works transparently:

// Creating a product now automatically stores the event in outbox
var response = await createProductUseCase.Execute(new CreateProductRequest(
    new ProductDetails("New Product", "Description"),
    stock: 10,
    price: 99.99m
));

// Event will be processed and published by the background service
// within 10 seconds, with automatic retry on failures

Configuration

The background service is automatically registered in dependency injection:

builder.Services
    .AddScoped<IOutboxRepository, OutboxRepository>()
    .AddScoped<IOutboxProcessor, OutboxProcessor>()
    .AddHostedService<OutboxBackgroundService>();

Fixes #45.

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[ElectNewt]

please address the comments

[ElectNewt]

you dn't need this

[Copilot]

You're right, I've removed the unused AddOutboxMessage method. The use cases now only use CreateRecordWithOutboxMessage and UpdateProductWithOutboxMessage methods which handle the outbox pattern transactionally. Fixed in commit e4b89ec.

[ElectNewt]

this is an indirection layer that it is not needed

[Copilot]

Agreed, I've removed the OutboxRepository indirection layer and moved the outbox operations directly to ProductsWriteStore. OutboxProcessor now depends on IProductsWriteStore directly, simplifying the architecture while maintaining the same functionality. Fixed in commit e4b89ec.