microsoft · Chris Anderson (codemonkeychris) · Jul 21, 2026 · Jul 21, 2026
@@ -90,4 +90,11 @@
     <PackageReference Include="Microsoft.WindowsAppSDK.Runtime" Condition="'$(_ReactorWinAppSDKFrameworkDependentApp)' == 'true'" />
   </ItemGroup>
 
+  <!-- Make the GitHub.Copilot.SDK build-time CLI download resilient on offline /
+       restricted networks so `dotnet build` / `dotnet run` works for everyone; see
+       the target's own comment. Imported here (a late import) so $(CopilotCliVersion)
+       and the SDK's $(_CopilotPlatform)/$(_CopilotBinary) are already resolved. -->
+  <Import Project="$(MSBuildThisFileDirectory)build\Reactor.CopilotCli.targets"
+          Condition="Exists('$(MSBuildThisFileDirectory)build\Reactor.CopilotCli.targets')" />
+
 </Project>
@@ -0,0 +1,158 @@
+<Project>
+
+  <!--
+    Resilient, internal/external-aware Copilot CLI acquisition for
+    GitHub.Copilot.SDK consumers (widget-creator, demo-script-tool, Reactor.Cli).
+
+    THE PROBLEM
+    The SDK's GitHub.Copilot.SDK.targets fetch the native `copilot.exe` at build
+    time with an unauthenticated MSBuild <DownloadFile> hardcoded to
+    registry.npmjs.org, then <Error> if it can't. That download:
+      * HARD-FAILS the build (MSB3923) on any offline / proxied / TLS-intercepted
+        network, and
+      * cannot use an authenticated Azure Artifacts npm feed (DownloadFile has no
+        credential support; Azure Artifacts npm feeds have no anonymous read).
+    See upstream github/copilot-sdk#921. The CLI is only a RUNTIME artifact — it is
+    not needed to compile — yet its download breaks `dotnet build` / `dotnet run`.
+
+    The SDK resolves the CLI at run time from COPILOT_CLI_PATH or the build-bundled
+    binary only (it does NOT download at run time), so we cannot simply skip: we
+    want to still bundle the pinned CLI whenever we can.
+
+    THE FIX (this file)
+    Take over acquisition ourselves whenever the SDK is referenced and neither the
+    developer nor CI has already pinned/skipped it, and turn OFF the SDK's own
+    hard-failing download. We decide this at EVALUATION time (this file is imported
+    from Directory.Build.targets AFTER the SDK's package targets, so the value we
+    evaluate for CopilotSkipCliDownload is the one the SDK targets' Conditions see —
+    a value set inside a BeforeTargets hook would be too late). We then obtain the
+    binary best-effort, in preference order, and place it in the output exactly like
+    the SDK would:
+
+      (1) A binary cached by a previous build              -> reuse it.
+      (2) COPILOT_CLI_PATH -> a local copilot(.exe)        -> bundle that.
+      (3) Public registry (external/OSS) -> <DownloadFile>  (auth-less, fast).
+      (4) `npm pack` honoring the ambient .npmrc            -> the supported path for
+          an AUTHENTICATED internal Azure Artifacts npm feed (internal dev/CI); also
+          a proxy-friendly fallback when (3) is blocked.
+      (5) Nothing worked -> warn and build WITHOUT a bundled CLI. The build still
+          succeeds; the app resolves the CLI at run time via COPILOT_CLI_PATH.
+
+    INTERNAL vs EXTERNAL
+      * External / OSS: the committed nuget.config + .npmrc stay on nuget.org /
+        registry.npmjs.org. (3) downloads the CLI directly. Nothing to configure.
+      * Internal: the build environment points npm at the internal Azure Artifacts
+        feed via an authenticated .npmrc (CI writes one; see build/pipelines). (4)
+        `npm pack` then resolves the CLI through that feed. Set CopilotNpmRegistryUrl
+        to force a specific registry; otherwise the ambient .npmrc registry is used.
+
+    Only active when GitHub.Copilot.SDK is referenced ($(CopilotCliVersion) is set by
+    its props). Inert when CopilotSkipCliDownload=true (CI default, see
+    Directory.Build.props) or the developer pinned CopilotCliBinaryPath.
+  -->
+
+  <PropertyGroup Condition="'$(CopilotCliVersion)' != '' and '$(_CopilotPlatform)' != '' and '$(CopilotSkipCliDownload)' != 'true' and '$(CopilotCliBinaryPath)' == ''">
+    <!-- We manage acquisition: disable the SDK's own download/copy/register targets
+         (they gate off CopilotSkipCliDownload) and bundle the CLI ourselves. -->
+    <_ReactorCopilotManage>true</_ReactorCopilotManage>
+    <CopilotSkipCliDownload>true</CopilotSkipCliDownload>
+
+    <_ReactorCopilotCacheDir>$(IntermediateOutputPath)copilot-cli\$(CopilotCliVersion)\$(_CopilotPlatform)</_ReactorCopilotCacheDir>
+    <_ReactorCopilotCacheBin>$(_ReactorCopilotCacheDir)\$(_CopilotBinary)</_ReactorCopilotCacheBin>
+    <_ReactorCopilotRegistry>$([System.String]::Copy('$(CopilotNpmRegistryUrl)').TrimEnd('/'))</_ReactorCopilotRegistry>
+    <_ReactorCopilotRegistry Condition="'$(_ReactorCopilotRegistry)' == ''">https://registry.npmjs.org</_ReactorCopilotRegistry>
+    <_ReactorCopilotRegistryIsPublic>false</_ReactorCopilotRegistryIsPublic>
+    <_ReactorCopilotRegistryIsPublic Condition="'$(_ReactorCopilotRegistry)' == 'https://registry.npmjs.org'">true</_ReactorCopilotRegistryIsPublic>
+  </PropertyGroup>
+
+  <!-- Obtain the CLI into the SDK's cache path, best-effort. Everything is
+       ContinueOnError so a restricted network / missing npm can't break the build. -->
+  <Target Name="_ReactorAcquireCopilotCli"
+          Condition="'$(_ReactorCopilotManage)' == 'true' and '$(TargetFramework)' != ''"
+          BeforeTargets="BeforeBuild">
+
+    <PropertyGroup>
+      <_ReactorCopilotTgzUrl>$(_ReactorCopilotRegistry)/@github/copilot-$(_CopilotPlatform)/-/copilot-$(_CopilotPlatform)-$(CopilotCliVersion).tgz</_ReactorCopilotTgzUrl>
+      <_ReactorCopilotArchive>$(_ReactorCopilotCacheDir)\copilot.tgz</_ReactorCopilotArchive>
+      <_ReactorCopilotNpmTgz>$(_ReactorCopilotCacheDir)\github-copilot-$(_CopilotPlatform)-$(CopilotCliVersion).tgz</_ReactorCopilotNpmTgz>
+      <_ReactorCopilotNpmRegistryArg Condition="'$(_ReactorCopilotRegistryIsPublic)' != 'true'"> --registry $(_ReactorCopilotRegistry)</_ReactorCopilotNpmRegistryArg>
+      <_ReactorCopilotTar Condition="$([MSBuild]::IsOSPlatform('Windows'))">$(SystemRoot)\System32\tar.exe</_ReactorCopilotTar>
+      <_ReactorCopilotTar Condition="'$(_ReactorCopilotTar)' == ''">tar</_ReactorCopilotTar>
+    </PropertyGroup>
+
+    <MakeDir Condition="!Exists('$(_ReactorCopilotCacheBin)')" Directories="$(_ReactorCopilotCacheDir)" />
+
+    <!-- (2) Developer-provided local CLI. -->
+    <Copy Condition="!Exists('$(_ReactorCopilotCacheBin)') and '$(COPILOT_CLI_PATH)' != '' and Exists('$(COPILOT_CLI_PATH)')"
+          SourceFiles="$(COPILOT_CLI_PATH)"
+          DestinationFiles="$(_ReactorCopilotCacheBin)"
+          SkipUnchangedFiles="true"
+          ContinueOnError="true" />
+
+    <!-- (3) Public registry: direct, auth-less download. -->
+    <DownloadFile Condition="!Exists('$(_ReactorCopilotCacheBin)') and '$(_ReactorCopilotRegistryIsPublic)' == 'true'"
+                  SourceUrl="$(_ReactorCopilotTgzUrl)"
+                  DestinationFolder="$(_ReactorCopilotCacheDir)"
+                  DestinationFileName="copilot.tgz"
+                  ContinueOnError="true" />
+    <Exec Condition="!Exists('$(_ReactorCopilotCacheBin)') and Exists('$(_ReactorCopilotArchive)')"
+          Command="&quot;$(_ReactorCopilotTar)&quot; -xzf &quot;$(_ReactorCopilotArchive)&quot; --strip-components=1 -C &quot;$(_ReactorCopilotCacheDir)&quot;"
+          ContinueOnError="true" />
+
+    <!-- (4) Authenticated internal feed (or proxy fallback): `npm pack` honors the
+         ambient .npmrc credentials that DownloadFile cannot use. -->
+    <Exec Condition="!Exists('$(_ReactorCopilotCacheBin)')"
+          Command="npm pack @github/copilot-$(_CopilotPlatform)@$(CopilotCliVersion)$(_ReactorCopilotNpmRegistryArg) --pack-destination &quot;$(_ReactorCopilotCacheDir)&quot;"
+          ContinueOnError="true" />
+    <Exec Condition="!Exists('$(_ReactorCopilotCacheBin)') and Exists('$(_ReactorCopilotNpmTgz)')"
+          Command="&quot;$(_ReactorCopilotTar)&quot; -xzf &quot;$(_ReactorCopilotNpmTgz)&quot; --strip-components=1 -C &quot;$(_ReactorCopilotCacheDir)&quot;"
+          ContinueOnError="true" />
+
+    <!-- (5) Give up gracefully. -->
+    <Warning Condition="!Exists('$(_ReactorCopilotCacheBin)')"
+             Code="REACTORCLI001"
+             Text="Copilot CLI $(CopilotCliVersion) could not be acquired (offline, restricted network, or no authenticated npm feed). Building '$(MSBuildProjectName)' without a bundled CLI. Set the COPILOT_CLI_PATH environment variable to a local Copilot CLI binary to enable generation at run time; internal builds should point npm at the internal Azure Artifacts feed (see build/pipelines)." />
+  </Target>
+
+  <!-- Register the bundled CLI as content so it flows to this project's output and
+       any referencing project. Mirrors the SDK's _RegisterCopilotCliForCopy but is a
+       no-op (no <Error>) when acquisition produced no binary. -->
+  <Target Name="_ReactorRegisterCopilotCli"
+          Condition="'$(_ReactorCopilotManage)' == 'true' and '$(TargetFramework)' != ''"
+          DependsOnTargets="_ReactorAcquireCopilotCli"
+          BeforeTargets="GetCopyToOutputDirectoryItems">
+    <PropertyGroup>
+      <_ReactorCopilotRuntimeNode>$(_ReactorCopilotCacheDir)\prebuilds\$(_CopilotPlatform)\runtime.node</_ReactorCopilotRuntimeNode>
+    </PropertyGroup>
+    <ItemGroup Condition="Exists('$(_ReactorCopilotCacheBin)')">
+      <ContentWithTargetPath Include="$(_ReactorCopilotCacheBin)"
+                             TargetPath="runtimes\$(_CopilotRid)\native\$(_CopilotBinary)"
+                             CopyToOutputDirectory="PreserveNewest" />
+      <ContentWithTargetPath Include="$(_ReactorCopilotRuntimeNode)"
+                             TargetPath="runtimes\$(_CopilotRid)\native\$(_CopilotRuntimeLib)"
+                             CopyToOutputDirectory="PreserveNewest"
+                             Condition="Exists('$(_ReactorCopilotRuntimeNode)')" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Copy the bundled CLI into this project's output runtimes folder. Mirrors the
+       SDK's _CopyCopilotCliToOutput; guarded on Exists so it is a no-op when absent. -->
+  <Target Name="_ReactorCopyCopilotCliToOutput"
+          Condition="'$(_ReactorCopilotManage)' == 'true' and '$(TargetFramework)' != '' and Exists('$(_ReactorCopilotCacheBin)')"
+          DependsOnTargets="_ReactorAcquireCopilotCli"
+          AfterTargets="Build">
+    <PropertyGroup>
+      <_ReactorCopilotOutDir>$(OutDir)runtimes\$(_CopilotRid)\native</_ReactorCopilotOutDir>
+      <_ReactorCopilotRuntimeNode>$(_ReactorCopilotCacheDir)\prebuilds\$(_CopilotPlatform)\runtime.node</_ReactorCopilotRuntimeNode>
+    </PropertyGroup>
+    <MakeDir Directories="$(_ReactorCopilotOutDir)" />
+    <Copy SourceFiles="$(_ReactorCopilotCacheBin)"
+          DestinationFiles="$(_ReactorCopilotOutDir)\$(_CopilotBinary)"
+          SkipUnchangedFiles="true" />
+    <Copy SourceFiles="$(_ReactorCopilotRuntimeNode)"
+          DestinationFiles="$(_ReactorCopilotOutDir)\$(_CopilotRuntimeLib)"
+          SkipUnchangedFiles="true"
+          Condition="Exists('$(_ReactorCopilotRuntimeNode)')" />
+  </Target>
+
+</Project>
@@ -27,7 +27,13 @@ parameters:
   - name: npmRegistry
     displayName: 'Internal npm registry (ADO feed) for transitive npm downloads.'
     type: string
-    default: 'https://github-private.pkgs.visualstudio.com/microsoft/_packaging/microsoft-ui-reactor/npm/registry/'
+    # Modern pkgs.dev.azure.com domain (org/project scoped), matching nuget.internal.config's
+    # feed. Equivalent to the legacy https://github-private.pkgs.visualstudio.com/microsoft/...
+    # form; the pkgs.dev.azure.com domain is Microsoft's preferred/required endpoint (agent
+    # firewall rules, reliability). The `microsoft-ui-reactor` feed proxies registry.npmjs.org
+    # via its npm upstream source, so transitive npm downloads (e.g. the GitHub.Copilot.SDK CLI)
+    # resolve internally with feed auth.
+    default: 'https://pkgs.dev.azure.com/github-private/microsoft/_packaging/microsoft-ui-reactor/npm/registry/'
   - name: version
     displayName: 'Explicit version; "auto" or blank => MinVer.'
     type: string

@@ -69,6 +69,28 @@ dotnet run --project samples/apps/widget-creator/widget-creator.csproj -p:Platfo
    feed. Run `mur pack-local` if it's missing. Override the feed path with
    `WIDGET_CREATOR_NUPKGS`.
 
+### The Copilot CLI at build time (internal vs external)
+
+The `GitHub.Copilot.SDK` bundles a native `copilot.exe` that it downloads at
+**build** time from an npm registry. The repo makes this resilient for everyone
+(`build/Reactor.CopilotCli.targets`), so `dotnet build` / `dotnet run` never
+hard-fails on a restricted network:
+
+- **External / OSS** — the committed `nuget.config` + `.npmrc` stay on public
+  `nuget.org` / `registry.npmjs.org`; the CLI downloads directly. Nothing to set up.
+- **Internal (Microsoft)** — point npm at the internal Azure Artifacts feed
+  (`https://pkgs.dev.azure.com/github-private/microsoft/_packaging/microsoft-ui-reactor/npm/registry/`)
+  via an authenticated `.npmrc` (CI does this automatically; locally use
+  `az artifacts` or the feed's *Connect to feed* → npm instructions). The build then
+  acquires the CLI through that feed with `npm pack`, since Azure Artifacts feeds
+  require auth that the SDK's raw download can't provide.
+- **Offline / no feed** — the build still succeeds *without* a bundled CLI (a
+  `REACTORCLI001` warning is emitted). To run generation you then need a Copilot
+  CLI binary available at run time: set `COPILOT_CLI_PATH` to a local `copilot.exe`
+  (or install the standalone Copilot CLI in its default per-user location). Note
+  `gh auth` only supplies Copilot credentials — it is not itself a runnable
+  `copilot.exe`.
+
 Type a prompt, click **Generate & Run**. The generated source streams into the
 right panel; the build + `wxc-exec` log streams below it. The widget window opens
 sandboxed — close it to finish the run. If it crashes instead, the creator keeps

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using System.Threading;
 using System.Threading.Channels;
 using System.Threading.Tasks;
@@ -42,6 +44,18 @@ async Task<CopilotClient> GetClientAsync(CancellationToken ct)
         {
             if (_client is not null) return _client;
             var options = new CopilotClientOptions();
+            // The SDK's default stdio transport looks ONLY for a CLI bundled next to
+            // the app (runtimes/<rid>/native/copilot.exe) and does not consult
+            // COPILOT_CLI_PATH. On builds where the CLI could not be bundled at build
+            // time (offline / restricted-network / authenticated-feed environments —
+            // see build/Reactor.CopilotCli.targets), resolve one at run time and pass
+            // it explicitly so generation still works.
+            var cliPath = ResolveCliPath();
+            if (cliPath is not null)
+            {
+                SessionLog.Write($"[CopilotSdk] no bundled CLI; using resolved CLI at {cliPath}");
+                options.Connection = RuntimeConnection.ForStdio(path: cliPath);
+            }
             var client = new CopilotClient(options);
             SessionLog.Write($"[CopilotSdk] starting CLI server (model={_model})");
             await client.StartAsync().ConfigureAwait(false);
@@ -55,6 +69,44 @@ async Task<CopilotClient> GetClientAsync(CancellationToken ct)
         }
     }
 
+    /// <summary>
+    /// Resolves a Copilot CLI to spawn when the SDK's bundled binary is absent.
+    /// Returns <c>null</c> when the bundled CLI is present (let the SDK use it) or
+    /// when nothing could be found (let the SDK throw its descriptive error).
+    /// Order: bundled next to the app → <c>COPILOT_CLI_PATH</c> → a locally
+    /// installed Copilot CLI in its well-known per-user location. We deliberately
+    /// do NOT probe <c>PATH</c> for <c>copilot.exe</c> — that would let any
+    /// unrelated (or malicious) binary earlier on <c>PATH</c> be launched. To use
+    /// a CLI in a non-standard location, set <c>COPILOT_CLI_PATH</c> explicitly.
+    /// </summary>
+    static string? ResolveCliPath()
+    {
+        var rid = "win-" + (RuntimeInformation.ProcessArchitecture == Architecture.Arm64 ? "arm64" : "x64");
+        var bundled = Path.Combine(AppContext.BaseDirectory, "runtimes", rid, "native", "copilot.exe");
+        if (File.Exists(bundled))
+            return null; // SDK's default resolution works.
+
+        var env = Environment.GetEnvironmentVariable("COPILOT_CLI_PATH");
+        if (!string.IsNullOrWhiteSpace(env) && File.Exists(env))
+            return env;
+
+        foreach (var candidate in EnumerateInstalledCliPaths())
+            if (File.Exists(candidate))
+                return candidate;
+
+        return null;
+    }
+
+    static IEnumerable<string> EnumerateInstalledCliPaths()
+    {
+        // Standalone GitHub Copilot CLI install (winget / gh), in its well-known
+        // per-user location. Intentionally a fixed, trusted path — never a PATH
+        // scan, so an unrelated copilot.exe on PATH can't be picked up and run.
+        var localAppData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
+        if (!string.IsNullOrEmpty(localAppData))
+            yield return Path.Combine(localAppData, "GitHub CLI", "copilot", "copilot.exe");
+    }
+
     public async Task<IModelConversation> StartConversationAsync(string systemPrompt, CancellationToken ct)
     {
         var client = await GetClientAsync(ct).ConfigureAwait(false);

@@ -25,12 +25,12 @@ public static class MxcBinaryManifest
         {
             ["win-arm64"] = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
             {
-                ["winhttp-proxy-shim.exe"] = "aca7cd110b09a1045c53a5c9bd73089f63e6c66f0b3d2627a5bdfb55bb524fdc",
-                ["wxc-exec.exe"] = "e430d0e4f44f616e91db684f8d825a6dc93e06a1262b8d00bcaac7522a317aab",
-                ["wxc-host-prep.exe"] = "3ef702332286a39153fc259310b5021e3de3c191751d7522684f6475f73af5ef",
-                ["wxc-test-proxy.exe"] = "1d1a5821a65c9b4aceb2f1788ca54b08d06b92b784daa1926ab978f4a49f1f00",
-                ["wxc-windows-sandbox-daemon.exe"] = "fc8079bddf5db77ee4ecea91d7f22a543fbec3618945a7ab97269dcfef3f66b1",
-                ["wxc-windows-sandbox-guest.exe"] = "69c972ce4a65d337f15d828e40b92fcb2f89665d32f2cb598606b45c76adfde3",
+                ["winhttp-proxy-shim.exe"] = "f1fdf37c66af032f4472f5de24fae766544d2fac19da75e45cecb38c5437caa8",
+                ["wxc-exec.exe"] = "d12957f434871af4cee0fbccfe12a91a615d3e91d8b81c7713f4141eb1f466df",
+                ["wxc-host-prep.exe"] = "ec91ae4a8d8b537b11c8401f3c1efd7ffc0fb4fba26d0f822f5138aa6cb08aee",
+                ["wxc-test-proxy.exe"] = "553fbc073ff820b674a87e0a348ddb8814031144812e5df2bc87e4ce7ba34ffa",
+                ["wxc-windows-sandbox-daemon.exe"] = "68054c012e8fcea6f8b82336edad58f96debb4d02b6f0a145befd9d7eaf301c1",
+                ["wxc-windows-sandbox-guest.exe"] = "985b88a7871653518f6db0103abf491c2e510be2405bf6a3dff8e64dece7f6f2",
             },
             ["win-x64"] = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
             {