Fix RS0017 enforcement via WarningsAsErrors in csproj

Agent-Logs-Url: https://github.com/petesramek/polyline-algorithm-csharp/sessions/1c652162-2d70-48dc-a57e-4a97a697213e

Co-authored-by: petesramek <2333452+petesramek@users.noreply.github.com>

Author: Copilot

.editorconfig

@@ -275,5 +275,5 @@ dotnet_naming_style.underscore_camel_case.capitalization = camel_case
 
 dotnet_public_api_analyzer.require_api_files = true
 
-# RS0017: Symbol removed from public API - always an error (breaking change detection)
+# RS0017: Symbol removed from public API - error severity (IDE guidance; build enforcement via WarningsAsErrors in .csproj)
 dotnet_diagnostic.RS0017.severity = error

src/PolylineAlgorithm/PolylineAlgorithm.csproj

@@ -8,6 +8,13 @@
 		<GenerateDocumentationFile>True</GenerateDocumentationFile>
 	</PropertyGroup>
 
+	<PropertyGroup>
+		<!-- RS0017: Symbol removed from public API — hard error so breaking changes can never be
+		     silently committed. The editorconfig dotnet_diagnostic setting alone is not honoured
+		     by MSBuild for third-party NuGet analyzers; WarningsAsErrors is required. -->
+		<WarningsAsErrors>$(WarningsAsErrors);RS0017</WarningsAsErrors>
+	</PropertyGroup>
+
 	<PropertyGroup>
 		<PublishRepositoryUrl>true</PublishRepositoryUrl>
 	</PropertyGroup>