[1/n] Implement RFC 003: MCP Infrastructure + Echo Env

Core MCP infrastructure:
- Add mcp_types.py with ListToolsAction, CallToolAction, observations
- Add mcp_environment.py with MCPEnvironment base class
- Update http_server.py with /mcp JSON-RPC endpoint
- Add mcp/fastmcp dependencies to pyproject.toml

Echo env conversion:
- Add mcp_server.py with echo_message tool
- Update echo_environment.py to use MCPEnvironment
- Update client.py with MCP action support
- Remove deprecated EchoAction/EchoObservation (models.py)

Tests and examples:
- Add tests/core/mcp/test_mcp.py
- Add examples/echo_mcp_demo.py

Author: Darktex

examples/echo_mcp_demo.py

@@ -0,0 +1,56 @@
+"""
+Example: Using Echo Environment with MCP
+
+This example demonstrates:
+1. Connecting to echo_env server
+2. Listing available tools via MCP
+3. Calling tools using the step() API
+"""
+
+import asyncio
+
+try:
+    from core.env_server.types import CallToolAction, ListToolsAction
+except ImportError:
+    from openenv_core.env_server.types import CallToolAction, ListToolsAction
+
+from envs.echo_env import EchoEnv
+
+
+async def main():
+    # Connect to echo_env (assumes server is running on localhost:8000)
+    # To start the server: uvicorn envs.echo_env.server.app:app
+    client = EchoEnv(base_url="http://localhost:8000")
+
+    print("=== Echo Environment MCP Demo ===\n")
+
+    # Reset the environment
+    print("1. Resetting environment...")
+    result = client.reset()
+    print(f"   Reset result: {result.observation.metadata}\n")
+
+    # List available tools using step API
+    print("2. Listing available tools...")
+    list_action = ListToolsAction()
+    list_result = client.step(list_action)
+    for tool in list_result.observation.tools:
+        print(f"   - {tool['name']}: {tool['description']}")
+    print()
+
+    # Call echo_message tool using step API
+    print("3. Calling echo_message tool...")
+    call_action = CallToolAction(tool_name="echo_message", parameters={"message": "Hello from MCP!"})
+    call_result = client.step(call_action)
+    print(f"   Result: {call_result.observation.result}\n")
+
+    # Check environment state
+    print("4. Checking environment state...")
+    state = client.state
+    print(f"   Episode ID: {state.episode_id}")
+    print(f"   Step count: {state.step_count}\n")
+
+    print("Demo complete!")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())

examples/test_mcp_integration.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Quick test script to verify MCP integration works."""
+
+import asyncio
+import sys
+sys.path.insert(0, 'src')
+
+from envs.echo_env.server.echo_environment import EchoEnvironment
+from core.env_server.types import ListToolsAction, CallToolAction
+
+
+async def main():
+    print("=" * 60)
+    print("Testing MCP Integration")
+    print("=" * 60)
+
+    # Create echo environment (MCPEnvironment handles MCP setup automatically)
+    print("\n1. Creating Echo Environment...")
+    env = EchoEnvironment()
+
+    # Test list tools
+    print("\n2. Testing ListToolsAction...")
+    list_action = ListToolsAction()
+    obs = await env._handle_mcp_action(list_action)
+    print(f"   - Done: {obs.done}")
+    print(f"   - Has 'tools' attribute: {hasattr(obs, 'tools')}")
+    if hasattr(obs, "tools"):
+        print(f"   - Number of tools: {len(obs.tools)}")
+        print(f"   - Tool names: {[t['name'] for t in obs.tools]}")
+    else:
+        print("   - ERROR: No 'tools' attribute!")
+        return False
+
+    # Test call tool
+    print("\n3. Testing CallToolAction...")
+    call_action = CallToolAction(
+        tool_name="echo_message",
+        parameters={"message": "Hello MCP!"}
+    )
+    obs = await env._handle_mcp_action(call_action)
+    print(f"   - Done: {obs.done}")
+    print(f"   - Has 'result' attribute: {hasattr(obs, 'result')}")
+    print(f"   - Error: {obs.error}")
+    if hasattr(obs, "result") and obs.result is not None:
+        result = obs.result
+        print(f"   - Result type: {type(result)}")
+        print(f"   - Result: {result}")
+    else:
+        print("   - ERROR: No 'result' attribute or result is None!")
+        return False
+
+    print("\n" + "=" * 60)
+    print("✅ All tests passed!")
+    print("=" * 60)
+    return True
+
+
+if __name__ == "__main__":
+    success = asyncio.run(main())
+    sys.exit(0 if success else 1)