Usercontrol: if changed manually from a page or similar

_This issue has been moved from [a ticket on Developer Community](https://developercommunity.visualstudio.com/t/Usercontrol:-if-changed-manually-from-a-/10961837)._

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[severity:It bothers me. A fix would be nice]
If a WPF UserControl or Page XAML file is missing its required .xaml.cs code-behind file, the build should fail with an error, not silently succeed. This causes hard-to-diagnose runtime issues.

the solution is built without errors and says no binding errors, but navigation silently fails, no errors or warning found.

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### Original Comments

#### Feedback Bot on 9/8/2025, 09:53 AM:

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