diff --git a/.github/workflows/validate-task.yml b/.github/workflows/validate-task.yml
index 6dd21b7..a204f6d 100644
--- a/.github/workflows/validate-task.yml
+++ b/.github/workflows/validate-task.yml
@@ -62,9 +62,18 @@ jobs:
       - name: Check EditorConfig step
         run: docker run --rm -v "$PWD":/check --workdir /check mstruebing/editorconfig-checker:latest
 
-      # --collect drives coverlet.collector to emit Cobertura XML into ./coverage/<guid>/.
+      # global.json opts into the native Microsoft.Testing.Platform runner, so the VSTest bridge
+      # (and its --collect data collector) is gone.
+      # --coverage-output stays unset because pinning one filename gives every test project in the solution the same path, and the last to finish overwrites the rest.
+      # The default <guid>.cobertura.xml written instead is a name codecov-cli's finder does not match, so each report is prefixed rather than renamed, keeping the guid that makes it unique.
       - name: Run unit tests step
-        run: dotnet test --collect:"XPlat Code Coverage" --results-directory ./coverage
+        run: |
+          set -Eeuo pipefail
+          dotnet test --coverage --coverage-output-format cobertura --results-directory ./coverage
+          for report in ./coverage/*.cobertura.xml; do
+            [ -e "$report" ] || continue
+            mv "$report" "./coverage/coverage-$(basename "$report")"
+          done
 
       # Report-only: fail_ci_if_error is false so a Codecov hiccup or an absent token never fails the gate.
       - name: Upload coverage to Codecov step
diff --git a/.gitignore b/.gitignore
index e255b63..67a587d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,9 @@
 .artifacts
 .DS_Store
 *.user
+
+# Coverage output (dotnet Microsoft.Testing.Extensions.CodeCoverage)
+coverage/
+[Tt]est[Rr]esults/
+*.cobertura.xml
+*.coverage
diff --git a/AGENTS.md b/AGENTS.md
index 94e6ff6..1a0fb71 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -40,6 +40,12 @@ For comprehensive coding and formatting standards, follow:
   - `version --versionpath=./Make/Version.json`.
   - `matrix --versionpath=./Make/Version.json --matrixpath=./Make/Matrix.json --updateversion`.
   - `make --versionpath=./Make/Version.json --makedirectory=./Make --dockerdirectory=./Docker --versionlabel=Beta`.
+- Tests run on the native Microsoft.Testing.Platform runner, opted into by `global.json`. Locally that is
+  plain `dotnet test`; CI adds coverage with
+  `dotnet test --coverage --coverage-output-format cobertura --results-directory ./coverage`, then prefixes
+  each report to `coverage-<guid>.cobertura.xml` so codecov-cli's file finder matches it. Running an
+  MTP-based test project through the VSTest target is what fails, so the old
+  `--collect:"XPlat Code Coverage"` form is an error here specifically because this project opted in.
 - Formatting and style checks are enforced by Husky.Net and VS Code tasks.
 - Required tasks are documented in `CODESTYLE.md` and `.husky/task-runner.json`.
 - C# code should be formatted with CSharpier, then verified with `dotnet format` (style).
diff --git a/CreateMatrixTests/CreateMatrixTests.csproj b/CreateMatrixTests/CreateMatrixTests.csproj
index 8152695..fe1756a 100644
--- a/CreateMatrixTests/CreateMatrixTests.csproj
+++ b/CreateMatrixTests/CreateMatrixTests.csproj
@@ -8,18 +8,14 @@
     <TargetFramework>net10.0</TargetFramework>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="AwesomeAssertions" Version="9.5.0" />
+    <PackageReference Include="AwesomeAssertions" Version="9.6.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.9.0" />
-    <PackageReference Include="xunit.v3" Version="3.2.2" />
-    <PackageReference Include="xunit.analyzers" Version="1.27.0">
+    <PackageReference Include="xunit.v3" Version="4.0.0" />
+    <PackageReference Include="xunit.analyzers" Version="2.0.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5" PrivateAssets="All" />
-    <PackageReference Include="coverlet.collector" Version="10.0.1">
-      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
-      <PrivateAssets>all</PrivateAssets>
-    </PackageReference>
+    <PackageReference Include="Microsoft.Testing.Extensions.CodeCoverage" Version="18.9.0" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\CreateMatrix\CreateMatrix.csproj" />
diff --git a/global.json b/global.json
new file mode 100644
index 0000000..3140116
--- /dev/null
+++ b/global.json
@@ -0,0 +1,5 @@
+{
+  "test": {
+    "runner": "Microsoft.Testing.Platform"
+  }
+}