fix: fall back to portable RID for bundled CLI lookup on Linux (#424)

On Linux distros that install .NET from distribution packages (Ubuntu,
Fedora, RHEL, etc.), RuntimeInformation.RuntimeIdentifier returns
distro-specific RIDs like ubuntu.24.04-x64 instead of the portable
linux-x64. The bundled CLI is placed under runtimes/linux-x64/native/,
so the lookup fails and throws.

Fix both the runtime lookup and build-time RID resolution:

- Client.cs: GetBundledCliPath now falls back to the portable RID
  (e.g., linux-x64) when the distro-specific RID path doesn't exist.
- GitHub.Copilot.SDK.targets: Always use portable RIDs derived from
  OS/architecture detection instead of the project's RuntimeIdentifier,
  which may be distro-specific.

Fixes #424

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

dotnet/src/Client.cs

@@ -997,11 +997,32 @@ private async Task VerifyProtocolVersionAsync(Connection connection, Cancellatio
     private static string? GetBundledCliPath(out string searchedPath)
     {
         var binaryName = OperatingSystem.IsWindows() ? "copilot.exe" : "copilot";
-        var rid = Path.GetFileName(System.Runtime.InteropServices.RuntimeInformation.RuntimeIdentifier);
+        // Always use portable RID (e.g., linux-x64) to match the build-time placement,
+        // since distro-specific RIDs (e.g., ubuntu.24.04-x64) are normalized at build time.
+        var rid = GetPortableRid()
+            ?? Path.GetFileName(System.Runtime.InteropServices.RuntimeInformation.RuntimeIdentifier);
         searchedPath = Path.Combine(AppContext.BaseDirectory, "runtimes", rid, "native", binaryName);
         return File.Exists(searchedPath) ? searchedPath : null;
     }
 
+    private static string? GetPortableRid()
+    {
+        string os;
+        if (OperatingSystem.IsWindows()) os = "win";
+        else if (OperatingSystem.IsLinux()) os = "linux";
+        else if (OperatingSystem.IsMacOS()) os = "osx";
+        else return null;
+
+        var arch = System.Runtime.InteropServices.RuntimeInformation.OSArchitecture switch
+        {
+            System.Runtime.InteropServices.Architecture.X64 => "x64",
+            System.Runtime.InteropServices.Architecture.Arm64 => "arm64",
+            _ => null,
+        };
+
+        return arch != null ? $"{os}-{arch}" : null;
+    }
+
     private static (string FileName, IEnumerable<string> Args) ResolveCliCommand(string cliPath, IEnumerable<string> args)
     {
         var isJsFile = cliPath.EndsWith(".js", StringComparison.OrdinalIgnoreCase);

dotnet/src/build/GitHub.Copilot.SDK.targets

@@ -3,17 +3,30 @@
   <!-- CopilotCliVersion is imported from GitHub.Copilot.SDK.props (generated at SDK build time, packaged alongside) -->
   <Import Project="$(MSBuildThisFileDirectory)GitHub.Copilot.SDK.props" Condition="'$(CopilotCliVersion)' == '' And Exists('$(MSBuildThisFileDirectory)GitHub.Copilot.SDK.props')" />
 
-  <!-- Resolve RID: use explicit RuntimeIdentifier, or infer from current machine -->
+  <!-- Resolve RID: honor explicit portable RuntimeIdentifier for cross-platform builds,
+       fall back to OS/arch detection only when RuntimeIdentifier is not set -->
   <PropertyGroup>
-    <_CopilotRid Condition="'$(RuntimeIdentifier)' != ''">$(RuntimeIdentifier)</_CopilotRid>
-    <_CopilotRid Condition="'$(_CopilotRid)' == '' And $([MSBuild]::IsOSPlatform('Windows')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'X64'">win-x64</_CopilotRid>
-    <_CopilotRid Condition="'$(_CopilotRid)' == '' And $([MSBuild]::IsOSPlatform('Windows')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'Arm64'">win-arm64</_CopilotRid>
-    <_CopilotRid Condition="'$(_CopilotRid)' == '' And $([MSBuild]::IsOSPlatform('Linux')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'X64'">linux-x64</_CopilotRid>
-    <_CopilotRid Condition="'$(_CopilotRid)' == '' And $([MSBuild]::IsOSPlatform('Linux')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'Arm64'">linux-arm64</_CopilotRid>
-    <_CopilotRid Condition="'$(_CopilotRid)' == '' And $([MSBuild]::IsOSPlatform('OSX')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'X64'">osx-x64</_CopilotRid>
-    <_CopilotRid Condition="'$(_CopilotRid)' == '' And $([MSBuild]::IsOSPlatform('OSX')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'Arm64'">osx-arm64</_CopilotRid>
+    <!-- Use explicit RuntimeIdentifier if it matches a supported portable RID -->
+    <_CopilotRid Condition="'$(RuntimeIdentifier)' == 'win-x64'">win-x64</_CopilotRid>
+    <_CopilotRid Condition="'$(RuntimeIdentifier)' == 'win-arm64'">win-arm64</_CopilotRid>
+    <_CopilotRid Condition="'$(RuntimeIdentifier)' == 'linux-x64'">linux-x64</_CopilotRid>
+    <_CopilotRid Condition="'$(RuntimeIdentifier)' == 'linux-arm64'">linux-arm64</_CopilotRid>
+    <_CopilotRid Condition="'$(RuntimeIdentifier)' == 'osx-x64'">osx-x64</_CopilotRid>
+    <_CopilotRid Condition="'$(RuntimeIdentifier)' == 'osx-arm64'">osx-arm64</_CopilotRid>
+    <!-- Detect from build host only when no explicit RuntimeIdentifier is set -->
+    <_CopilotRid Condition="'$(_CopilotRid)' == '' And '$(RuntimeIdentifier)' == '' And $([MSBuild]::IsOSPlatform('Windows')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'X64'">win-x64</_CopilotRid>
+    <_CopilotRid Condition="'$(_CopilotRid)' == '' And '$(RuntimeIdentifier)' == '' And $([MSBuild]::IsOSPlatform('Windows')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'Arm64'">win-arm64</_CopilotRid>
+    <_CopilotRid Condition="'$(_CopilotRid)' == '' And '$(RuntimeIdentifier)' == '' And $([MSBuild]::IsOSPlatform('Linux')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'X64'">linux-x64</_CopilotRid>
+    <_CopilotRid Condition="'$(_CopilotRid)' == '' And '$(RuntimeIdentifier)' == '' And $([MSBuild]::IsOSPlatform('Linux')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'Arm64'">linux-arm64</_CopilotRid>
+    <_CopilotRid Condition="'$(_CopilotRid)' == '' And '$(RuntimeIdentifier)' == '' And $([MSBuild]::IsOSPlatform('OSX')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'X64'">osx-x64</_CopilotRid>
+    <_CopilotRid Condition="'$(_CopilotRid)' == '' And '$(RuntimeIdentifier)' == '' And $([MSBuild]::IsOSPlatform('OSX')) And '$([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture)' == 'Arm64'">osx-arm64</_CopilotRid>
   </PropertyGroup>
 
+  <!-- Fail early if an explicit RID was given but not recognized -->
+  <Target Name="_ValidateCopilotRid" BeforeTargets="BeforeBuild" Condition="'$(RuntimeIdentifier)' != '' And '$(_CopilotRid)' == ''">
+    <Error Text="RuntimeIdentifier '$(RuntimeIdentifier)' is not a supported portable RID for the Copilot CLI. Supported RIDs: win-x64, win-arm64, linux-x64, linux-arm64, osx-x64, osx-arm64." />
+  </Target>
+
   <!-- Map RID to platform name used in npm packages -->
   <PropertyGroup>
     <_CopilotPlatform Condition="'$(_CopilotRid)' == 'win-x64'">win32-x64</_CopilotPlatform>