fix(csharp-ci): match CodeCoverage 18.9.0 relocated cobertura output

.github/workflows/csharp-ci.yaml

@@ -142,18 +142,20 @@ on:
         default: 'C# coverage'
       tests-glob:
         description: >-
-          Glob (relative to working-directory) used to locate the per-project
-          `*.cobertura.xml` files emitted by MTP's coverage extension. The
-          matching files are union-merged into a single report
-          (`coverage/merged.cobertura.xml`) by `dotnet-coverage merge`
-          before irongut/CodeCoverageSummary summarizes it. The default
-          narrows to `bin/Release/net*/` so that stale cobertura files
-          left over in source-controlled or scratch directories do not get
-          merged. Adjust if your tests live outside a top-level `tests/`
-          directory or target a non-Release configuration.
+          Space-separated glob(s), relative to working-directory, used to
+          locate the `*.cobertura.xml` files emitted by MTP's coverage
+          extension. All matching files are union-merged into
+          `coverage/merged.cobertura.xml` by `dotnet-coverage merge` before
+          irongut/CodeCoverageSummary summarizes it. The defaults cover the
+          two places the toolchain writes coverage output — each test
+          project's `bin/Release/` tree and the run-level `TestResults/`
+          directory — while staying narrow enough to skip stale files in
+          source-controlled or scratch directories. Adjust if your tests
+          live outside a top-level `tests/` directory or target a
+          non-Release configuration.
         required: false
         type: string
-        default: 'tests/**/bin/Release/net*/**/*.cobertura.xml'
+        default: 'tests/**/bin/Release/net*/**/*.cobertura.xml TestResults/**/*.cobertura.xml'
       pack:
         description: >-
           Whether to run `dotnet pack` and upload the resulting .nupkg as a

README.md

@@ -187,9 +187,11 @@ stay on a previous SHA / tag until you've migrated the items below.
     across files fails the coverage shard loud — like a missing
     `global.json`. The version must be a literal (e.g. `18.8.0`).
   See [`canton-ledger-api-csharp#79`](https://github.com/peacefulstudio/canton-ledger-api-csharp/pull/79)
-  for the MTP 1.x / 2.x compatibility rationale: do not bump
-  `CodeCoverage` past 18.0.x until `xunit.v3` ships an MTP 2.x build —
-  newer 19.x lines have produced empty Cobertura output in this pipeline.
+  for the MTP 1.x / 2.x compatibility rationale: the 18.0.x ceiling
+  applied until `xunit.v3` shipped its MTP 2.x package. With
+  `xunit.v3.mtp-v2` in place, 18.x lines through 18.9.x are supported —
+  but newer 19.x lines have produced empty Cobertura output in this
+  pipeline.
 
 - **`tests/Directory.Build.props`** (or equivalent) must enable MTP:
 
@@ -200,16 +202,27 @@ stay on a previous SHA / tag until you've migrated the items below.
   ```
 
   The exact arguments live in the caller — what matters is that MTP runs
-  in-process and emits `*.cobertura.xml` files somewhere under `tests/`.
-
-- **Multi-TFM test projects** must set a per-TFM Cobertura filename to
-  avoid silent overwrites between target frameworks:
+  in-process and emits `*.cobertura.xml` files. Their location depends on
+  the toolchain combination: CodeCoverage 18.9.0 together with .NET SDK
+  10.0.3xx relocates the relative `--coverage-output` file to
+  `<working-directory>/TestResults/` (the run-level results directory),
+  whereas with an older package line or SDK 10.0.1xx they land under each
+  test project's `tests/**/bin/Release/<tfm>/TestResults/`. The default
+  `tests-glob` matches both layouts.
+
+- **Multi-TFM test projects** must set a Cobertura filename that is unique
+  per project *and* per TFM to avoid silent overwrites — under the relocated
+  layout (CodeCoverage 18.9.0 + SDK 10.0.3xx) every project writes into the
+  shared `<working-directory>/TestResults/`, so a project-name prefix is
+  what keeps two projects from clobbering each other's files:
 
   ```xml
   <TestingPlatformCommandLineArguments>... --coverage-output $(MSBuildProjectName)_$(TargetFramework).cobertura.xml</TestingPlatformCommandLineArguments>
   ```
 
-  Single-TFM projects can omit this.
+  The `$(MSBuildProjectName)` prefix satisfies both. Single-TFM projects in
+  the per-project layout can omit this, but the project-name prefix is
+  still required to stay collision-free in the shared directory.
 
 - **`coverage.settings.xml`** at the repo root (or wherever
   `TestingPlatformCommandLineArguments` points), tuning the coverage