docs: fix langgraph comparison and add MIT license

- Correct middleware claim: langgraph has graph-level middleware
- Replace debuggability claim with honest observability comparison
- Add LICENSE file

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: xfgong

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 xf gong
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -16,8 +16,8 @@ Inspired by [pi-agent-core](https://github.com/anthropics/pi-agent-core) (TypeSc
 | **Dependencies** | Pulls in langchain-core, langgraph-sdk, and transitive deps | 3 core deps: `pydantic`, `anthropic`, `openai` |
 | **Tool execution** | Tools are graph nodes with manual wiring | Declare tools as functions, framework handles routing and parallel execution |
 | **Multi-provider** | Via langchain chat model adapters | Native Provider protocol — Anthropic, OpenAI built in, add your own with one class |
-| **Middleware** | Not built in — use langchain callbacks or custom graph nodes | First-class middleware protocol with 5 composable hooks |
-| **Debuggability** | Trace through graph execution, channel updates, checkpoint diffs | Linear execution flow — set a breakpoint in the loop, see exactly what's happening |
+| **Middleware** | Graph-level middleware on node entry/exit | Agent-level middleware with 5 typed hooks and declarative composition rules |
+| **Observability** | LangSmith / Langfuse integration, full trace visualization | Events + middleware hooks — bring your own tracing |
 
 ### vs pi-agent-core