The `_currentTransaction` field is added to a singleton `MauiEventsBinder` and accessed from multiple event handlers (`OnShellOnNavigating`, `OnApplicationOnModalPushed`, `OnApplicationOnModalPopped`, `OnWindowOnStopped`) without thread synchronization. These handlers can fire concurrently from different navigation events. The `StartNavigationTransaction` method has a TOCTOU race where it checks `_currentTransaction is { IsFinished: false }` and then conditionally finishes or resets it - another thread could modify `_currentTransaction` between the check and the subsequent operations.

The new `ChildSpanFinished()` method checks `_hasFinished` and then calls `_idleTimer?.Start()`, but the timer can be disposed by a concurrent `Finish()` call between these operations. This is the same race condition that `ResetIdleTimeout()` handles with a try-catch block, but `ChildSpanFinished()` lacks this protection. When `SpanTracer.Finish()` calls `Transaction.ChildSpanFinished()`, if `TransactionTracer.Finish()` is called concurrently, an unhandled `ObjectDisposedException` will propagate up to the caller.