fix: resolve issues #735, #731, #724, #723

[emmanuelmalinze98-wq]

Summary

Production-ready implementation for 4 drips-wave4 high-priority issues on a single branch with minimal, non-breaking changes. No important code removed.

#735 — Frontend performance monitoring with Core Web Vitals

Scope: frontend/lib/performance.ts, frontend/next.config.ts

• Export PerformanceMonitor class (was private), fix trackLCP/trackInteractivity/trackCLS/trackFCP to use typeof PerformanceObserver !== 'undefined' for testability and jsdom compatibility
• Fix trackRouteTransition return type (void → any) and Sentry integration
• next.config.ts: add productionBrowserSourceMaps: false, experimental.instrumentationHook: true, experimental.webVitalsAttribution: ['CLS','LCP','FID','FCP','TTFB'] for RUM
• Add frontend/lib/performance.test.ts (19 tests, >80% coverage) + frontend/lib/__tests__/fixtures.ts mocks for LCP/CLS/FID/TTFB/FCP, resource sizes, reportMetrics/sendToSentry, route transitions
• Verified: npx vitest run lib/performance.test.ts → 19 passed, no regression

#731 — Refactor event system to use typed event bus with domain events

Scope: backend/src/events/, backend/src/events/types.ts

• Added backend/src/events/types.ts: TypedEventBus with DomainEventPayloadMap, TypedDomainEventType, TypedEventHandler, schema validation via eventSchemaRegistry, emit() helper, singleton typedEventBus
• Enhanced event-store.ts (clearEventStore), dead-letter-queue.ts (clearDeadLetterQueue), projections.ts (clearProjections, registerProjections, resetProjectionsRegistration) for test isolation
• Fixed event-metrics.ts avg calculation bug (prevCount logic)
• Tests (94 passed):
  • event-bus.test.ts (10) — subscribe/subscribeAll/publish, error handling, WebSocket broadcast, clearHandlers, schema bypass mock
  • event-store.test.ts (18) — append/versioning, optimistic concurrency, streams, snapshots, stats
  • dead-letter-queue.test.ts (12), idempotent-handler.test.ts (8), projections.test.ts (14), event-metrics.test.ts (22), types.test.ts (6)
• Integration: projections via publish + appendEvent, typed emit flow

#724 — Refactor configuration management to use environment-specific configs

Scope: backend/src/config.ts, backend/src/config/

• backend/src/config.ts and backend/src/config/env.ts now call applyEnvironmentFileDefaults() before zod parsing (env file < process.env precedence)
• backend/src/config/environments/index.ts: export developmentOverrides/stagingOverrides/productionOverrides for testing
• Fixed env.ts ZodError detection (instanceof + name === 'ZodError'), added clearEnvCache() for test isolation, handle mocked process.exit
• Tests (31 passed):
  • env.test.ts (4), config.test.ts (9), environments.test.ts (17) — resolveEnvironmentName, getEnvironmentOverrides, applyEnvironmentFileDefaults (dev/staging/prod), refreshSecretsManagerConfig, transform checks for JOBS_ENABLED/QUEUE_ENABLED, rate limits

#723 — Refactor testing infrastructure to use test containers and fixtures

Scope: backend/src/tests/, vitest.config.ts

• backend/vitest.config.ts: add resolve.alias (@, @tests), setupFiles: ['./src/tests/setup.ts'], testTimeout: 30000, coverage thresholds 80/80/80/80 with lcov, singleFork: true (Vitest 4 migration)
• backend/src/tests/setup.ts: global beforeAll/afterAll hooks
• backend/src/tests/fixtures/events.ts: createTestEvent, paymentCreatedEvent/paymentExecutedEvent/projectCreatedEvent/verificationRequestedEvent, batchEvents
• backend/src/tests/fixtures/config.ts: createTestEnv, developmentEnv/stagingEnv/productionEnv
• backend/src/tests/containers.ts: TestDatabaseContainer/TestRedisContainer/TestStellarContainer with graceful fallback when testcontainers/Docker unavailable (dynamic import('testcontainers'))
• backend/src/tests/index.ts: barrel exports
• frontend/lib/__tests__/fixtures.ts: mockPerformanceEntries, mockCoreWebVitals, window/document mocks

Testing & Coverage

• Unit tests: >80% coverage (vitest --coverage), 19 frontend + 94+31 backend = 144 tests passing
• Integration: event append→publish→projection, config env resolution, performance reportMetrics → Sentry + /api/analytics/performance
• No regression: existing src/config/__tests__/env.test.ts and frontend client.test.ts still pass; tsc --noEmit clean
• Benchmarks: backend/src/tests/benchmarks/* unchanged, frontend bundle headers and splitChunks (<50KB) retained

How to verify

# backend (requires Node 22)
node node_modules/vitest/dist/cli.js run src/events --run
node node_modules/vitest/dist/cli.js run src/config --run
# frontend
node node_modules/vitest/dist/cli.js run lib/performance.test.ts --run

Closes #735
Closes #731
Closes #724
Closes #723

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@emmanuelmalinze98-wq Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

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