The DebounceAsync_LeadingMode_DebounceSubsequentCalls test was flaky, failing intermittently with execution count of 3 instead of expected 2.

Root Cause

Race condition in DebounceDispatcher.cs: the CancellationTokenSource was captured outside the lock, allowing multiple concurrent calls to capture the same instance.

// Before - race condition
finally { _lock.Release(); }
var localCts = _cancellationTokenSource;  // ← captured after lock release

// After - fixed
CancellationTokenSource? localCts = null;
// ... inside lock:
_cancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
localCts = _cancellationTokenSource;  // ← captured before lock release
finally { _lock.Release(); }

Changes

Implementation (DebounceDispatcher.cs)

• Declare localCts at method scope
• Capture CTS reference inside lock before release

Test (DebounceDispatcherTests.cs)

• Store task references and explicitly await them instead of fire-and-forget with Task.Delay(150)
• Eliminates timing assumptions, ensures proper synchronization

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