feat: add ACT+ECT over MCP demo with LangGraph agent

End-to-end PoC demonstrating Agent Context Token authorization and
Execution Context Token accountability over MCP tool calls, using a
LangGraph agent with ES256-signed JWT tokens and DAG verification.

demo/act-ect-mcp/pyproject.toml

@@ -0,0 +1,48 @@
+[build-system]
+requires = ["setuptools>=68"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "act-ect-poc"
+version = "0.1.0"
+description = "End-to-end PoC: LangGraph agent calling MCP tools with ACT mandate + ECT execution context"
+requires-python = ">=3.11"
+dependencies = [
+    # Our refimpls (installed from sibling packages)
+    "ietf-act",
+    "ietf-ect",
+    # MCP server + client
+    "mcp>=1.6.0",
+    # LangGraph + LLM plumbing
+    "langgraph>=0.3.0",
+    "langchain>=0.3.0",
+    "langchain-core>=0.3.0",
+    "langchain-ollama>=0.2.0",
+    "langchain-mcp-adapters>=0.1.0",
+    # HTTP server + client
+    "fastapi>=0.110",
+    "uvicorn[standard]>=0.29",
+    "httpx>=0.27",
+    # Crypto / JWT
+    "cryptography>=42.0",
+    "PyJWT>=2.8.0",
+]
+
+[project.optional-dependencies]
+dev = ["pytest>=8.0", "pytest-asyncio>=0.23"]
+
+[project.scripts]
+poc-server = "poc.server:main"
+poc-agent = "poc.agent:main"
+poc-verify = "poc.verify_cli:main"
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.uv.sources]
+ietf-act = { path = "../../workspace/packages/act", editable = true }
+ietf-ect = { path = "../../workspace/packages/ect", editable = true }
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+asyncio_mode = "auto"