[hubbuugittuuu]

Summary

This PR adds comprehensive unit and regression test coverage for pauseGuard middleware in backend/src/middleware/__tests__/pauseGuard.test.ts, addressing concurrent pause state transitions, mid-flight loan mutation races, and exempt route boundary rules.

Closes #2093

Details of Changes

• Concurrent State Transitions & Race Conditions:
  • Validates that concurrent invocations of setPauseState preserve valid in-memory state without race condition corruptions.
  • Tests rapid transition from unpaused to paused, verifying immediate rejection of mutating loan operations (/api/loans/disburse) with 503 AppError.
  • Tests transition from paused to unpaused, ensuring subsequent mutating operations (/api/loans/repay) are permitted through to next().
• Error Formatting & Fallbacks:
  • Asserts error message formatting and fallback handling when reason is null or omitted, verifying Maintenance or security measure default.
• Fail-Open Database Resilience:
  • Verifies that when database synchronization query fails, pauseGuard fails open gracefully and preserves existing in-memory state.
• Exempt Route Boundary Verification:
  • Tests exact prefix matches for exempt routes (/api/auth/login, /api/v1/auth/session, /api/admin/recovery, /api/v1/admin/unpause, /admin/status).
  • Verifies that non-exempt or partially matching routes (/api/authentication/login, /api/administrator/kill, /api/loans/repay, /api/v1/loans/apply, /api/contracts/invoke) remain strictly blocked during an active pause.

Verification & CI Proof

• npm run lint: Passed (0 errors)
• npm run build: Passed (0 errors)
• npm test -- src/middleware/__tests__/pauseGuard.test.ts: 28/28 tests passing (100% green)
• Full backend test suite: 125 test suites passed (1102 tests green)