diff --git a/src/Infrastructure/BotSharp.Abstraction/Functions/IMcpHttpFunctionRouter.cs b/src/Infrastructure/BotSharp.Abstraction/Functions/IMcpHttpFunctionRouter.cs
new file mode 100644
index 00000000..2461544b
--- /dev/null
+++ b/src/Infrastructure/BotSharp.Abstraction/Functions/IMcpHttpFunctionRouter.cs
@@ -0,0 +1,21 @@
+using BotSharp.Abstraction.Agents.Models;
+using BotSharp.Abstraction.Routing.Executor;
+
+namespace BotSharp.Abstraction.Functions;
+
+/// <summary>
+/// W4C extension point: resolves an <see cref="IFunctionExecutor"/> for MCP tools served by
+/// dynamically-configured <b>Streamable HTTP</b> servers (user custom MCP servers and the built-in
+/// OpenPencil design server). BotSharp's stock <c>McpClientManager</c> only reaches SSE/Stdio
+/// servers registered at startup, so hosts that talk to streamable-HTTP servers register an
+/// implementation of this and <see cref="Routing.Executor.FunctionExecutorFactory"/> consults it
+/// before its own executors. Return <c>null</c> to let the stock executors handle the function.
+/// </summary>
+public interface IMcpHttpFunctionRouter
+{
+    /// <summary>
+    /// Returns an executor for <paramref name="functionName"/> when it belongs to a routed MCP server
+    /// the host can reach over streamable HTTP, otherwise <c>null</c>.
+    /// </summary>
+    IFunctionExecutor? Create(Agent agent, string functionName);
+}
diff --git a/src/Infrastructure/BotSharp.Core/Routing/Executor/FunctionExecutorFactory.cs b/src/Infrastructure/BotSharp.Core/Routing/Executor/FunctionExecutorFactory.cs
index 8a4a5486..93a93d6b 100644
--- a/src/Infrastructure/BotSharp.Core/Routing/Executor/FunctionExecutorFactory.cs
+++ b/src/Infrastructure/BotSharp.Core/Routing/Executor/FunctionExecutorFactory.cs
@@ -13,6 +13,21 @@ internal class FunctionExecutorFactory
             return new FunctionCallbackExecutor(functionCall);
         }
 
+        // W4C: route MCP tools served by dynamically-configured Streamable HTTP servers (custom MCP
+        // servers and the OpenPencil design server) that the stock McpClientManager (SSE/Stdio only)
+        // cannot reach. The host's router resolves the owning server itself, so it also covers
+        // "all tools" (empty function list) entries. Returns null when the function is not an MCP
+        // tool, letting the stock executors below handle it.
+        var w4c = services.GetService<IMcpHttpFunctionRouter>();
+        if (w4c != null)
+        {
+            var w4cExecutor = w4c.Create(agent, functionName);
+            if (w4cExecutor != null)
+            {
+                return w4cExecutor;
+            }
+        }
+
         var functions = (agent?.Functions ?? []).Concat(agent?.SecondaryFunctions ?? []);
         var funcDef = functions.FirstOrDefault(x => x.Name == functionName);
         if (!string.IsNullOrWhiteSpace(funcDef?.Output))