Add SEP-2640 Skills extension support

.github/scripts/prepare_markdown_links.py

@@ -0,0 +1,41 @@
+import argparse
+from pathlib import Path
+
+
+class RepositoryLinks:
+    def __init__(self, root):
+        self.root = Path(root).resolve()
+
+    def prepare(self):
+        docs = self.root / "docs"
+        if not docs.is_dir():
+            raise ValueError(f"Missing documentation directory: {docs}")
+        if docs.is_symlink():
+            raise ValueError(f"Refusing to rewrite a documentation symlink: {docs}")
+
+        changed = 0
+        prefixes = (
+            "https://github.com/modelcontextprotocol/csharp-sdk/tree/main/",
+            "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/",
+        )
+        for path in docs.rglob("*.md"):
+            if path.is_symlink():
+                raise ValueError(f"Refusing to rewrite a documentation symlink: {path}")
+            text = path.read_text(encoding="utf-8")
+            updated = text
+            for prefix in prefixes:
+                updated = updated.replace(prefix, "/")
+            if updated != text:
+                path.write_text(updated, encoding="utf-8")
+                changed += 1
+        return changed
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(
+        description="Resolve this repository's main-branch links against the proposed checkout for mlc."
+    )
+    parser.add_argument("root")
+    arguments = parser.parse_args()
+    count = RepositoryLinks(arguments.root).prepare()
+    print(f"Prepared repository-local links in {count} Markdown files; mlc still validates each target.")

.github/scripts/test_prepare_markdown_links.py

@@ -0,0 +1,47 @@
+from pathlib import Path
+import tempfile
+import unittest
+
+from prepare_markdown_links import RepositoryLinks
+
+
+class RepositoryLinksTests(unittest.TestCase):
+    def setUp(self):
+        self.directory = tempfile.TemporaryDirectory()
+        self.addCleanup(self.directory.cleanup)
+        self.root = Path(self.directory.name)
+        (self.root / "docs").mkdir()
+
+    def test_main_links_become_checkout_paths_without_ignoring_missing_targets(self):
+        path = self.root / "docs" / "example.md"
+        path.write_text(
+            "[sample](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/SkillsServer)\n"
+            "[source](https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/missing.cs)\n",
+            encoding="utf-8",
+        )
+
+        self.assertEqual(RepositoryLinks(self.root).prepare(), 1)
+        self.assertEqual(
+            path.read_text(encoding="utf-8"),
+            "[sample](/samples/SkillsServer)\n[source](/src/missing.cs)\n",
+        )
+
+    def test_other_repositories_and_pinned_revisions_remain_web_links(self):
+        path = self.root / "docs" / "example.md"
+        original = (
+            "[other](https://github.com/other/project/tree/main/sample)\n"
+            "[pinned](https://github.com/modelcontextprotocol/csharp-sdk/tree/1234567/sample)\n"
+            "[relative](other.md)\n"
+        )
+        path.write_text(original, encoding="utf-8")
+
+        self.assertEqual(RepositoryLinks(self.root).prepare(), 0)
+        self.assertEqual(path.read_text(encoding="utf-8"), original)
+
+    def test_missing_documentation_is_not_a_success(self):
+        with self.assertRaises(ValueError):
+            RepositoryLinks(self.root / "absent").prepare()
+
+
+if __name__ == "__main__":
+    unittest.main()

.github/workflows/markdown-link-check.yml

@@ -3,10 +3,18 @@ name: Check Markdown links
 on:
   push:
     branches: [ "main" ]
-    paths: "**.md"
+    paths:
+      - "**.md"
+      - ".github/scripts/prepare_markdown_links.py"
+      - ".github/scripts/test_prepare_markdown_links.py"
+      - ".github/workflows/markdown-link-check.yml"
   pull_request:
     branches: [ "main" ]
-    paths: "**.md"
+    paths:
+      - "**.md"
+      - ".github/scripts/prepare_markdown_links.py"
+      - ".github/scripts/test_prepare_markdown_links.py"
+      - ".github/workflows/markdown-link-check.yml"
 
 permissions:
   contents: read
@@ -18,6 +26,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
+      - name: Resolve main-branch links against the proposed checkout
+        run: |
+          python3 -m unittest discover -s .github/scripts -p test_prepare_markdown_links.py
+          python3 .github/scripts/prepare_markdown_links.py .
+
       - name: Markup Link Checker (mlc)
         uses: becheran/mlc@7ec24825cefe0c9c8c6bac48430e1f69e3ec356e # v1.2.0
         with:
@@ -26,6 +39,7 @@ jobs:
           # Do not warn for learn.microsoft.com locale redirects.
           # Do not warn for modelcontextprotocol.io homepage/spec redirects.
           args: >-
+            --root-dir .
             --ignore-links "xref:*"
             --ignore-links "*samples/*?name=snippet_*"
             --do-not-warn-for-redirect-to "https://learn.microsoft.com/en-us/*"

ModelContextProtocol.slnx

@@ -49,6 +49,8 @@
     <Project Path="samples/ProtectedMcpServer/ProtectedMcpServer.csproj" />
     <Project Path="samples/QuickstartClient/QuickstartClient.csproj" />
     <Project Path="samples/QuickstartWeatherServer/QuickstartWeatherServer.csproj" />
+    <Project Path="samples/SkillsClient/SkillsClient.csproj" />
+    <Project Path="samples/SkillsServer/SkillsServer.csproj" />
     <Project Path="samples/TasksExtension/TasksExtension.csproj" />
     <Project Path="samples/TestServerWithHosting/TestServerWithHosting.csproj" />
     <Project Path="samples/WeatherAppServer/WeatherAppServer.csproj" />
@@ -69,6 +71,7 @@
     <Project Path="src/ModelContextProtocol.AspNetCore/ModelContextProtocol.AspNetCore.csproj" />
     <Project Path="src/ModelContextProtocol.Core/ModelContextProtocol.Core.csproj" />
     <Project Path="src/ModelContextProtocol.Extensions.Apps/ModelContextProtocol.Extensions.Apps.csproj" />
+    <Project Path="src/ModelContextProtocol.Extensions.Skills/ModelContextProtocol.Extensions.Skills.csproj" />
     <Project Path="src/ModelContextProtocol.Extensions.Tasks/ModelContextProtocol.Extensions.Tasks.csproj" />
     <Project Path="src/ModelContextProtocol/ModelContextProtocol.csproj" />
   </Folder>

README.md

@@ -16,6 +16,8 @@ The SDK packages are:
 
 - **[ModelContextProtocol.Extensions.Apps](https://www.nuget.org/packages/ModelContextProtocol.Extensions.Apps)** [![NuGet version](https://img.shields.io/nuget/v/ModelContextProtocol.Extensions.Apps.svg)](https://www.nuget.org/packages/ModelContextProtocol.Extensions.Apps) - MCP Apps extension for building interactive UI applications that render inside MCP hosts.
 
+- **[ModelContextProtocol.Extensions.Skills](https://www.nuget.org/packages/ModelContextProtocol.Extensions.Skills)** [![NuGet version](https://img.shields.io/nuget/v/ModelContextProtocol.Extensions.Skills.svg)](https://www.nuget.org/packages/ModelContextProtocol.Extensions.Skills) - MCP Skills extension for serving and consuming Agent Skills with verifiable file manifests.
+
 - **[ModelContextProtocol.Extensions.Tasks](https://www.nuget.org/packages/ModelContextProtocol.Extensions.Tasks)** [![NuGet version](https://img.shields.io/nuget/v/ModelContextProtocol.Extensions.Tasks.svg)](https://www.nuget.org/packages/ModelContextProtocol.Extensions.Tasks) - MCP Tasks extension for running long-running tool invocations asynchronously with status polling and input requests.
 
 ## Getting Started

docs/concepts/index.md

@@ -53,4 +53,5 @@ To install the SDK and build your first MCP client and server, see [Getting star
 | - | - |
 | [MCP Apps](apps/apps.md) | Learn how to use the MCP Apps extension to deliver interactive UIs from MCP servers. |
 | [Tasks](tasks/tasks.md) | Learn how to use task-based execution for long-running operations that can be polled for status and results. |
+| [Skills](skills/skills.md) | Learn how to serve and consume Agent Skills over MCP, with verifiable file manifests. |
 | [Identity and Roles](identity/identity.md) | Learn how to access caller identity and roles in MCP tool, prompt, and resource handlers. |