refactor(mcp): simplify generated code via runtime invoker adapters

docs/asciidoc/modules/mcp.adoc

@@ -189,7 +189,7 @@ public class UserService {
 <1> Forces array schema generation for `User`, overriding generic `Object` erasure and the global/config flag.
 <2> Explicitly disables schema generation for this specific tool.
 
-=== Custom Invokers & Telemetry
+=== Custom Invokers
 
 You can inject custom logic (like SLF4J MDC context propagation, tracing, or custom error handling) around every tool, prompt, or resource execution by providing an `McpInvoker`.
 
@@ -204,16 +204,21 @@ Invokers are chained. You can register multiple invokers and they will wrap the
 ----
 import io.jooby.mcp.McpInvoker;
 import io.jooby.mcp.McpOperation;
+import io.jooby.mcp.McpChain;
+import io.modelcontextprotocol.common.McpTransportContext;
+import io.modelcontextprotocol.server.McpSyncServerExchange;
+import org.jspecify.annotations.Nullable;
 import org.slf4j.MDC;
 
 public class MdcMcpInvoker implements McpInvoker {
   @Override
-  public <R> R invoke(McpOperation operation, SneakyThrows.Supplier<R> action) {
+  public <R> R invoke(@Nullable McpSyncServerExchange exchange, McpTransportContext transportContext, McpOperation operation, McpChain chain) throws Exception {
     try {
-      MDC.put("mcp.id", operation.id());                 <1>
+      MDC.put("mcp.id", operation.id());                            // <1>
       MDC.put("mcp.class", operation.className());
       MDC.put("mcp.method", operation.methodName());
-      return action.get();                               <2>
+
+      return chain.proceed(exchange, transportContext, operation);  // <2>
     } finally {
       MDC.remove("mcp.id");
       MDC.remove("mcp.class");
@@ -224,13 +229,66 @@ public class MdcMcpInvoker implements McpInvoker {
 
 {
   install(new McpModule(new CalculatorServiceMcp_())
-      .invoker(new MdcMcpInvoker()));                    <3>
+      .invoker(new MdcMcpInvoker()));                               // <3>
 }
 ----
 
 <1> Extract rich contextual data from the `McpOperation` record.
-<2> Proceed with the execution chain.
-<3> Register the invoker. Jooby will safely map any business exceptions thrown by your action into valid MCP JSON-RPC errors.
+<2> Proceed to the next interceptor in the chain or execute the final target handler.
+<3> Register the invoker. Jooby will safely map any business exceptions thrown by your chain into valid MCP JSON-RPC errors.
+
+==== Context Augmentation
+
+You can use an `McpInvoker` to resolve contextual data (such as an authenticated user, a tenant ID, etc.) and inject it directly into the `McpOperation`.
+
+This allows your tool methods to simply declare the custom type in their method signature, keeping your business logic clean and completely decoupled from transport-layer extraction.
+
+.Context Injector Example
+[source, java]
+----
+import io.jooby.mcp.McpInvoker;
+import io.jooby.mcp.McpOperation;
+import io.jooby.mcp.McpChain;
+import io.modelcontextprotocol.common.McpTransportContext;
+import io.modelcontextprotocol.server.McpSyncServerExchange;
+import org.jspecify.annotations.Nullable;
+
+public class UserContextInvoker implements McpInvoker {
+  @Override
+  @SuppressWarnings("unchecked")
+  public <R> R invoke(@Nullable McpSyncServerExchange exchange, McpTransportContext transportContext, McpOperation operation, McpChain chain) throws Exception {
+
+    User currentUser = retrieveUser();
+
+    // 2. Augment the operation with the resolved user
+    operation.setArgument("user", currentUser);
+
+    // 3. Proceed with the augmented operation
+    return (R) chain.proceed(exchange, transportContext, augmentedOp);
+  }
+}
+----
+
+Once the invoker is registered, you can seamlessly declare the augmented argument in your MCP controllers. The Jooby Annotation Processor will automatically map the injected argument to your method parameter.
+
+.Tool Implementation
+[source, java]
+----
+import io.jooby.annotation.mcp.McpTool;
+
+public class BillingService {
+
+  /**
+   * @param user The authenticated user (injected by UserContextInvoker). 
+   * Note: Because it is a complex type not present in the JSON request, 
+   * it is safely ignored by the JSON schema generator.
+   */
+  @McpTool(description = "Retrieves the billing history for the current user")
+  public InvoiceHistory getMyInvoices(User user, int limit) {
+    return database.findInvoices(user.getId(), limit);
+  }
+}
+----
 
 === Multiple Servers
 

modules/jooby-apt/src/main/java/io/jooby/apt/JoobyProcessor.java

@@ -24,7 +24,7 @@
 import javax.tools.*;
 
 import io.jooby.internal.apt.*;
-
+import io.jooby.internal.apt.mcp.McpRouter;
 import io.jooby.internal.apt.ws.WsRouter;
 
 /** Process jooby/jakarta annotation and generate source code from MVC controllers. */

modules/jooby-apt/src/main/java/io/jooby/internal/apt/McpRoute.java → modules/jooby-apt/src/main/java/io/jooby/internal/apt/mcp/McpRoute.java

@@ -3,7 +3,7 @@
  * Apache License Version 2.0 https://jooby.io/LICENSE.txt
  * Copyright 2014 Edgar Espina
  */
-package io.jooby.internal.apt;
+package io.jooby.internal.apt.mcp;
 
 import static io.jooby.internal.apt.CodeBlock.*;
 import static io.jooby.internal.apt.CodeBlock.string;
@@ -15,6 +15,8 @@
 
 import javax.lang.model.element.ExecutableElement;
 
+import io.jooby.internal.apt.AnnotationSupport;
+import io.jooby.internal.apt.WebRoute;
 import io.jooby.javadoc.JavaDocNode;
 import io.jooby.javadoc.MethodDoc;
 
@@ -333,7 +335,8 @@ private List<String> generatePromptDefinition(boolean kt) {
       var type = param.getType().getRawType().toString();
       if (type.equals("io.modelcontextprotocol.server.McpSyncServerExchange")
           || type.equals("io.modelcontextprotocol.common.McpTransportContext")
-          || type.equals("io.jooby.Context")) continue;
+          || type.equals("io.jooby.Context")
+          || type.equals("io.jooby.mcp.McpOperation")) continue;
 
       var mcpName = param.getMcpName();
       var isRequired = !param.isNullable(kt);
@@ -461,7 +464,8 @@ private List<String> generateToolDefinition(boolean kt) {
       var type = param.getType().getRawType().toString();
       if (type.equals("io.modelcontextprotocol.server.McpSyncServerExchange")
           || type.equals("io.modelcontextprotocol.common.McpTransportContext")
-          || type.equals("io.jooby.Context")) continue;
+          || type.equals("io.jooby.Context")
+          || type.equals("io.jooby.mcp.McpOperation")) continue;
 
       var mcpName = param.getMcpName();
       var paramDescription = param.getMcpDescription();
@@ -809,15 +813,19 @@ public List<String> generateMcpHandlerMethod(boolean kt) {
               "private fun ",
               handlerName,
               "(exchange: io.modelcontextprotocol.server.McpSyncServerExchange?, transportContext:"
-                  + " io.modelcontextprotocol.common.McpTransportContext, req:"
-                  + " io.modelcontextprotocol.spec.McpSchema.",
-              reqType,
-              "): io.modelcontextprotocol.spec.McpSchema.",
+                  + " io.modelcontextprotocol.common.McpTransportContext, operation:"
+                  + " io.jooby.mcp.McpOperation): io.modelcontextprotocol.spec.McpSchema.",
               resType,
               " {"));
 
       buffer.add(
           statement(indent(6), "val ctx = transportContext.get(\"CTX\") as? io.jooby.Context"));
+      buffer.add(
+          statement(
+              indent(6),
+              "val req_ = operation.request(io.modelcontextprotocol.spec.McpSchema.",
+              reqType,
+              "::class.java)"));
     } else {
       buffer.add(
           statement(
@@ -827,37 +835,36 @@ public List<String> generateMcpHandlerMethod(boolean kt) {
               " ",
               handlerName,
               "(io.modelcontextprotocol.server.McpSyncServerExchange exchange,"
-                  + " io.modelcontextprotocol.common.McpTransportContext"
-                  + " transportContext,"
-                  + " io.modelcontextprotocol.spec.McpSchema.",
-              reqType,
-              " req) {"));
+                  + " io.modelcontextprotocol.common.McpTransportContext transportContext,"
+                  + " io.jooby.mcp.McpOperation operation) {"));
 
       buffer.add(
           statement(
               indent(6),
               "var ctx = (io.jooby.Context) transportContext.get(\"CTX\")",
               semicolon(kt)));
+      buffer.add(
+          statement(
+              indent(6),
+              "var req_ = operation.request(io.modelcontextprotocol.spec.McpSchema.",
+              reqType,
+              ".class)",
+              semicolon(kt)));
     }
 
     if (isMcpTool() || isMcpPrompt()) {
       if (kt) {
-        buffer.add(statement(indent(6), "val args = req.arguments() ?: emptyMap<String, Any>()"));
+        buffer.add(statement(indent(6), "val args = operation.arguments()"));
       } else {
-        buffer.add(
-            statement(
-                indent(6),
-                "var args = req.arguments() != null ? req.arguments() :"
-                    + " java.util.Collections.<String, Object>emptyMap()",
-                semicolon(kt)));
+        buffer.add(statement(indent(6), "var args = operation.arguments()", semicolon(kt)));
       }
     } else if (isMcpResource() || isMcpResourceTemplate()) {
       String uriTemplate = extractAnnotationValue("io.jooby.annotation.mcp.McpResource", "uri");
       boolean isTemplate = isMcpResourceTemplate();
 
       if (isTemplate) {
         if (kt) {
-          buffer.add(statement(indent(6), "val uri = req.uri()"));
+          buffer.add(statement(indent(6), "val uri = req_.uri()"));
           buffer.add(
               statement(
                   indent(6),
@@ -867,7 +874,7 @@ public List<String> generateMcpHandlerMethod(boolean kt) {
           buffer.add(statement(indent(6), "val args = mutableMapOf<String, Any>()"));
           buffer.add(statement(indent(6), "args.putAll(manager.extractVariableValues(uri))"));
         } else {
-          buffer.add(statement(indent(6), "var uri = req.uri()", semicolon(kt)));
+          buffer.add(statement(indent(6), "var uri = req_.uri()", semicolon(kt)));
           buffer.add(
               statement(
                   indent(6),
@@ -911,7 +918,11 @@ public List<String> generateMcpHandlerMethod(boolean kt) {
           || type.equals("io.modelcontextprotocol.common.McpTransportContext")) {
         continue;
       } else if (type.equals("io.modelcontextprotocol.spec.McpSchema." + reqType)) {
-        buffer.add(statement(indent(6), kt ? "val " : "var ", javaName, " = req", semicolon(kt)));
+        buffer.add(statement(indent(6), kt ? "val " : "var ", javaName, " = req_", semicolon(kt)));
+        continue;
+      } else if (type.equals("io.jooby.mcp.McpOperation")) {
+        buffer.add(
+            statement(indent(6), kt ? "val " : "var ", javaName, " = operation", semicolon(kt)));
         continue;
       }
 
@@ -1070,7 +1081,7 @@ public List<String> generateMcpHandlerMethod(boolean kt) {
 
     var methodCall = "c." + getMethodName() + "(" + String.join(", ", javaParamNames) + ")";
 
-    String toMethodPrefix = (isMcpResource() || isMcpResourceTemplate()) ? "req.uri(), " : "";
+    String toMethodPrefix = (isMcpResource() || isMcpResourceTemplate()) ? "req_.uri(), " : "";
 
     // Resolve output schema flag for Handler runtime behavior
     String toMethodSuffix = "";