Summary

Document the asynchronous database operations API at database/async/async_operations.h which provides non-blocking query execution.

Parent Issue

Part of: [EPIC] docs: Address documentation gaps across all ecosystem systems (kcenon/common_system#325)

Background (Why)

The async_operations.h module provides asynchronous database query execution, enabling non-blocking database access patterns. This is critical for high-throughput applications but is completely undocumented. Users must read source code to discover async capabilities.

Source files:

• database/async/async_operations.h — Async operation definitions

Scope (What)

Add async operations documentation covering:

1. Async Architecture Overview

• How async operations integrate with thread_system
• Callback vs future-based patterns
• Connection pool interaction in async context

2. API Reference

• All async operation functions/methods
• Parameter types and return types
• Future/promise types used
• Cancellation support

3. Usage Patterns

// Document patterns like:
auto future = db.async_query("SELECT * FROM users WHERE id = ?", {user_id});
auto result = future.get(); // blocking wait

// Or callback-based:
db.async_query("SELECT ...", {}, [](auto result) {
    // handle result
});

4. Error Handling

• Async-specific error scenarios
• Timeout handling
• Connection loss during async operation
• Retry strategies

5. Performance Considerations

• When to use async vs sync operations
• Connection pool sizing for async workloads
• Batching async operations
• Backpressure handling

6. Thread Safety

• Which async operations are thread-safe
• Shared state considerations
• Result object thread safety

Acceptance Criteria

• Async operations API fully documented
• Usage examples for both future and callback patterns
• Error handling patterns documented
• Thread safety guarantees stated
• Performance guidance provided
• Integration with thread_system explained