Merge branch 'main' into feature/sep-2106-output-schema-relaxation

Author: jayaraman-venkatesan

.github/workflows/ci-build-test.yml

@@ -52,7 +52,7 @@ jobs:
     - name: 🔧 Set up Node.js
       uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
       with:
-        node-version: '20'
+        node-version: '22'
 
     - name: 📦 Install pinned npm dependencies for tests
       run: npm ci

.gitignore

@@ -1,6 +1,9 @@
 # Cake tools
 /[Tt]ools/
 
+# Language server cache
+*.lscache
+
 # Build output
 [Bb]uildArtifacts/
 # Build results

docs/concepts/tools/tools.md

@@ -315,3 +315,28 @@ public static string Search(
     // Schema will include descriptions and default value for maxResults
 }
 ```
+
+### Custom HTTP headers from tool parameters
+
+When using the Streamable HTTP transport, tool parameters can be mirrored as HTTP headers so that network infrastructure (load balancers, proxies, gateways) can make routing decisions without parsing the JSON-RPC request body. Apply the <xref:ModelContextProtocol.Server.McpHeaderAttribute> to a parameter to opt it in:
+
+```csharp
+[McpServerTool, Description("Executes a SQL query in a specific region")]
+public static string ExecuteSql(
+    [McpHeader("Region"), Description("Target datacenter region")] string region,
+    [Description("The SQL query to execute")] string query)
+{
+    // Clients will send an additional HTTP header:
+    //   Mcp-Param-Region: <region value>
+}
+```
+
+When the tool's schema is generated, the annotated parameter includes an `x-mcp-header` extension property. Clients read this annotation and automatically add the corresponding `Mcp-Param-{Name}` header on outgoing `tools/call` requests. The server validates that the header value matches the value in the JSON-RPC body.
+
+Rules and constraints:
+
+- Only primitive parameter types (`string`, numeric types, `bool`) are supported.
+- The header name must contain only visible ASCII characters (0x21–0x7E) excluding colon (`:`).
+- Values containing non-ASCII characters, control characters, or leading/trailing whitespace are Base64-encoded using the `=?base64?{value}?=` wrapper.
+- Header names must be case-insensitively unique within the tool's input schema.
+- Header validation is enforced only for protocol versions that support the HTTP Standardization feature (currently `DRAFT-2026-v1` and later).

package-lock.json

@@ -2,7 +2,7 @@
   "private": true,
   "description": "Pinned npm dependencies for MCP C# SDK integration and conformance tests",
   "dependencies": {
-    "@modelcontextprotocol/conformance": "0.1.13",
+    "@modelcontextprotocol/conformance": "0.1.16",
     "@modelcontextprotocol/server-everything": "2026.1.26",
     "@modelcontextprotocol/server-memory": "2026.1.26"
   }