Add event-driven dashboard stats with product event tracking

[antosubash]

Summary

Implements an event-driven architecture for the Dashboard module to track product lifecycle events (create, update, delete) without direct coupling to the Products module. The EventBus is refactored to use pyee's AsyncIOEventEmitter for more robust async event handling.

Key Changes

Event Bus Refactoring

• Replaced custom event handler dictionary with pyee.asyncio.AsyncIOEventEmitter for more reliable async event dispatch
• Updated publish() to use asyncio.gather() for concurrent handler execution with error isolation
• Updated publish_nowait() to use pyee's native event emission
• Added error handler for background task failures

Product Events & Contracts

• Created products/contracts/events.py with domain events: ProductCreated, ProductUpdated, ProductDeleted
• Exported events from products/contracts/__init__.py for cross-module consumption
• Updated Products API endpoints to publish events after successful operations (create, update, delete)
• Added get_event_bus() dependency in products/deps.py to inject EventBus into endpoints

Dashboard Module Implementation

• Created dashboard/handlers.py with event handlers that maintain in-memory counters for product events
• Created dashboard/endpoints/api.py with /stats endpoint returning product event counts
• Updated DashboardModule to:
  • Register event handlers via register_event_handlers()
  • Set route prefix and module dependencies
  • Include API router
• Added Dashboard dependency on Products module

Testing

• Added comprehensive test suite (modules/dashboard/tests/test_dashboard.py) covering:
  • Individual handler unit tests
  • Module registration and event subscription
  • Stats API endpoint behavior and authentication
  • End-to-end integration tests (product CRUD → event bus → dashboard counters)
  • Edge cases (failed operations don't emit events, concurrent handler execution)
• Added EventBus tests for subclass event matching, concurrent dispatch, and edge cases

Dependencies

• Added pyee>=12.0 to framework/core dependencies
• Added products module as dependency for dashboard module

Notable Implementation Details

• Event handlers are strictly type-matched (subclass events don't trigger parent handlers)
• Failed product operations (404s) don't publish events—handlers execute after successful lookups
• Dashboard stats are read-only snapshots to prevent external mutation
• All event handlers run concurrently for better performance
• Error isolation ensures one handler failure doesn't prevent others from executing

https://claude.ai/code/session_01KLjCnJoNbCbk8is6pVZcom