Test-driven fixes for code review blockers NCS-16:
**Observable (CRITICAL):** Added synchronized blocks to subscribe, unsubscribe,
notifyObservers, and observerCount to prevent race conditions when concurrent
threads register observers while notifications are dispatched.
**CommandInvoker (IMPORTANT):** Added synchronized blocks to all methods
(execute, undo, redo, history, getCurrentIndex, canUndo, canRedo, clear) to
ensure atomic access to mutable state (executedCommands, currentIndex).
Tests:
- Added ObservableThreadSafetyTest: 3 tests for concurrent subscribe/unsubscribe/notify
- Added CommandInvokerThreadSafetyTest: 2 tests for concurrent execute/undo/redo
- All 54 existing tests remain green
- Full build passes with 100% core coverage
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Janis
8f64273ceb