Document breaking change: Code coverage EnableDynamicNativeInstrumentation defaults to false in .NET 10 (#49620)

Author: Copilot

docs/core/compatibility/10.0.md

@@ -117,6 +117,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 | [.NET CLI `--interactive` defaults to `true` in user scenarios](sdk/10.0/dotnet-cli-interactive.md) | Behavioral change | Preview 3 |
 | [`dotnet` CLI commands log non-command-relevant data to stderr](sdk/10.0/dotnet-cli-stderr-output.md) | Behavioral change | RC 2 |
 | [.NET tool packaging creates RuntimeIdentifier-specific tool packages](sdk/10.0/dotnet-tool-pack-publish.md) | Behavioral change | Preview 6 |
+| [Code coverage EnableDynamicNativeInstrumentation defaults to false](sdk/10.0/code-coverage-dynamic-native-instrumentation.md) | Behavioral change | GA |
 | [Default workload configuration from 'loose manifests' to 'workload sets' mode](sdk/10.0/default-workload-config.md) | Behavioral change | Preview 2 |
 | [dnx.ps1 file is no longer included in .NET SDK](sdk/10.0/dnx-ps1-removed.md) | Source incompatible | GA |
 | [Double quotes in file-level directives are disallowed](sdk/10.0/file-level-directive-double-quotes.md) | Source incompatible | GA |

docs/core/compatibility/sdk/10.0/code-coverage-dynamic-native-instrumentation.md

@@ -0,0 +1,66 @@
+---
+title: "Breaking change - Code coverage EnableDynamicNativeInstrumentation defaults to false"
+description: "Learn about the breaking change in .NET 10 where dynamic native instrumentation is disabled by default when collecting code coverage."
+ms.date: 11/05/2025
+ai-usage: ai-assisted
+ms.custom: https://github.com/dotnet/docs/issues/49376
+---
+
+# Code coverage EnableDynamicNativeInstrumentation defaults to false
+
+Running `dotnet test --collect:"Code Coverage"` now disables dynamic native instrumentation by default. This change affects how code coverage is collected from native code. It doesn't affect how code coverage is collected from managed code.
+
+## Version introduced
+
+.NET 10 GA
+
+## Previous behavior
+
+Previously, dynamic native instrumentation was enabled by default and used a fallback for native modules when static native instrumentation couldn't be used. This behavior is described in [Static and dynamic native instrumentation](/visualstudio/test/customizing-code-coverage-analysis?view=vs-2022#static-and-dynamic-native-instrumentation).
+
+```bash
+dotnet test --collect:"Code Coverage"
+# Dynamic native instrumentation was enabled by default
+```
+
+## New behavior
+
+Starting in .NET 10, dynamic native instrumentation is disabled by default. The `<EnableDynamicNativeInstrumentation>false</EnableDynamicNativeInstrumentation>` option is set by default from `dotnet test` and `vstest`. If you explicitly set the option in a *runsettings* file, it isn't overridden.
+
+```bash
+dotnet test --collect:"Code Coverage"
+# Dynamic native instrumentation is now disabled by default
+```
+
+You can re-enable dynamic native instrumentation by setting `<EnableDynamicNativeInstrumentation>true</EnableDynamicNativeInstrumentation>` in your *runsettings* file. However, when you do so, it might fail with "The code execution cannot proceed because covrun64.dll was not found." This error can also happen for `covrun32.dll` in a 32-bit process.
+
+## Type of breaking change
+
+This change is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+Dynamic native instrumentation was enabled by default to maintain backwards compatibility in `dotnet test`. However, its way of injecting DLLs into the process isn't standard. With [security hardening changes](https://github.com/dotnet/runtime/pull/112359) in the .NET 10 runtime, it fails to find the linked DLL, causing the process to [crash with error](https://github.com/dotnet/sdk/issues/50950). The error might not be visible in non-interactive sessions or in the command line, but the process does crash.
+
+Dynamic native instrumentation is already disabled by default by `dotnet-coverage`, which is an alternative way to collect code coverage using the same underlying tools. It's also disabled by default for solutions in Visual Studio that don't have native projects.
+
+## Recommended action
+
+If you collect coverage on solutions that don't have any native components, you shouldn't be affected. However, you might observe increased performance when collecting coverage.
+
+If you collect coverage on solutions that include native components, such as C++ projects, you have the following options:
+
+- Configure your projects to use [static native instrumentation](/visualstudio/test/customizing-code-coverage-analysis#static-and-dynamic-native-instrumentation)
+
+  OR
+
+- Update to Microsoft.CodeCoverage 18.0.1 and enable dynamic native instrumentation:
+
+  - Add the setting `<EnableDynamicNativeInstrumentation>true</EnableDynamicNativeInstrumentation>` to your *runsettings* file.
+  - Globally opt out from this new default by setting the `VSTEST_DISABLE_DYNAMICNATIVE_CODECOVERAGE_DEFAULT_SETTING=1` environment variable.
+
+  Similarly, when collecting code coverage with `vstest.console`, VSTest version 18.0.1 and newer is required to successfully collect dynamic native coverage on systems that have the .NET 10 SDK installed.
+
+## Affected APIs
+
+None.

docs/core/compatibility/toc.yml

@@ -126,6 +126,8 @@ items:
                 href: reflection/10/makegeneric-signaturetype-validation.md
           - name: SDK and MSBuild
             items:
+              - name: Code coverage EnableDynamicNativeInstrumentation defaults to false
+                href: sdk/10.0/code-coverage-dynamic-native-instrumentation.md
               - name: .NET CLI `--interactive` defaults to `true` in user scenarios
                 href: sdk/10.0/dotnet-cli-interactive.md
               - name: "`dotnet` CLI commands log non-command-relevant data to stderr"