add demo mcp example (remove jar before merging!!!)

distribution/examples/mcp/README.md

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+# MCP Tool Blocking with Membrane
+
+This example shows how to place a Membrane API Gateway in front of an MCP server and block a specific tool call based on the MCP request body.
+
+The backend MCP server exposes two tools:
+
+- `echo`
+- `secretHello`
+
+The setup is:
+
+- backend MCP server on `http://localhost:8081/mcp`
+- Membrane API Gateway on `http://localhost:2000/mcp`
+
+The gateway forwards all MCP requests to the backend, but blocks calls to `secretHello`.
+
+## Running the Example
+
+1. Go to this example directory.
+
+2. Start the backend MCP server.
+
+   Linux / macOS:
+   ```sh
+   ./start-backend.sh
+   ```
+
+   Windows:
+   ```bat
+   start-backend.cmd
+   ```
+
+3. Start Membrane.
+
+   Linux / macOS:
+   ```sh
+   ./membrane.sh
+   ```
+
+   Windows:
+   ```bat
+   membrane.cmd
+   ```
+
+4. Start the MCP Inspector:
+
+   ```sh
+   npx @modelcontextprotocol/inspector
+   ```
+
+5. Open the Inspector UI in your browser.
+
+6. Create a connection to the gateway with these values:
+
+    - **Transport:** `Streamable HTTP`
+    - **URL:** `http://localhost:2000/mcp`
+
+7. Connect.
+
+## Testing with the Inspector
+
+### 1. Inspect available tools
+
+Open the **Tools** section.
+
+You should see both backend tools:
+
+- `echo`
+- `secretHello`
+
+This example blocks the execution of one tool at the gateway layer. It does not remove the tool from `tools/list`.
+
+### 2. Call the allowed tool
+
+Select the `echo` tool and set the text to e.g. "Hello".
+
+### 3. Call the blocked tool
+
+Select the `secretHello` tool and use the same text:
+
+`Blocked by Membrane gateway: tool secretHello is not allowed`

distribution/examples/mcp/apis.yaml

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+api:
+  name: demo-mcp-gateway
+  port: 2000
+  path:
+    uri: /mcp
+  flow:
+    - request:
+        - if:
+            language: SpEL
+            test: "isJSON() and json.method == 'tools/call' and json['params'] != null and json['params']['name'] == 'secretHello'"
+            flow:
+              - template:
+                  contentType: application/json
+                  src: |
+                    {
+                      "jsonrpc": "2.0",
+                      "id": ${json.id},
+                      "result": {
+                        "content": [
+                          {
+                            "type": "text",
+                            "text": "Blocked by Membrane gateway: tool secretHello is not allowed"
+                          }
+                        ],
+                        "isError": true
+                      }
+                    }
+              - return:
+                  status: 200
+                  contentType: application/json
+
+    - log: {}
+
+  target:
+    host: localhost
+    port: 8081

distribution/examples/mcp/membrane.cmd

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+@echo off
+setlocal EnableExtensions
+
+set "SCRIPT_DIR=%~dp0"
+if "%SCRIPT_DIR:~-1%"=="\" set "SCRIPT_DIR=%SCRIPT_DIR:~0,-1%"
+
+set "dir=%SCRIPT_DIR%"
+
+:search_up
+if exist "%dir%\LICENSE.txt" if exist "%dir%\scripts\run-membrane.cmd" goto found
+for %%A in ("%dir%\..") do set "next=%%~fA"
+if /I "%next%"=="%dir%" goto notfound
+set "dir=%next%"
+goto search_up
+
+:found
+set "MEMBRANE_HOME=%dir%"
+set "MEMBRANE_CALLER_DIR=%SCRIPT_DIR%"
+call "%MEMBRANE_HOME%\scripts\run-membrane.cmd" %*
+exit /b %ERRORLEVEL%
+
+:notfound
+>&2 echo Could not locate Membrane root. Ensure directory structure is correct.
+exit /b 1

distribution/examples/mcp/membrane.sh

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+#!/bin/sh
+# Default: ./proxies.xml (next to this script); fallback -> $MEMBRANE_HOME/conf/proxies.xml
+# JAVA_OPTS: relative -D paths are auto-resolved against $MEMBRANE_HOME (absolute/URI unchanged).
+# Examples:
+#   export JAVA_OPTS='-Dlog4j.configurationFile=examples/logging/access/log4j2_access.xml'
+#   export JAVA_OPTS='-Dlog4j.configurationFile=/abs/path/log4j2.xml'
+
+SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd -P)
+
+dir="$SCRIPT_DIR"
+while [ "$dir" != "/" ]; do
+  if [ -f "$dir/LICENSE.txt" ] && [ -f "$dir/scripts/run-membrane.sh" ]; then
+    export MEMBRANE_HOME="$dir"
+    export MEMBRANE_CALLER_DIR="$SCRIPT_DIR"
+    exec sh "$dir/scripts/run-membrane.sh" "$@"
+  fi
+  dir=$(dirname "$dir")
+done
+
+echo "Could not locate Membrane root. Ensure directory structure is correct." >&2
+exit 1

distribution/examples/mcp/start-backend.cmd

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+@echo off
+setlocal
+cd /d "%~dp0"
+java -jar mcp-server-demo.jar

distribution/examples/mcp/start-backend.sh

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+#!/bin/sh
+SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd -P)
+cd "$SCRIPT_DIR" || exit 1
+exec java -jar ./mcp-server-demo.jar