refactor(lang): use OpenAI-compatible API for Gemini, update deps to langgraph 0.6

lang/agent/graph.py

@@ -2,17 +2,19 @@ import os
 from typing import Any, Dict
 
 from langchain.tools import tool
-from langchain_google_genai import ChatGoogleGenerativeAI
+from langchain_openai import ChatOpenAI
 from langgraph.prebuilt import create_react_agent
 from langchain_core.runnables import RunnableConfig
 from mcp_client import McpInvoker
 
 
-# Configure LLM (Gemini)
-def build_llm() -> ChatGoogleGenerativeAI:
-    return ChatGoogleGenerativeAI(
-        model=os.getenv("GOOGLE_VERTEX_MODEL", "gemini-1.5-pro"),
+# Configure LLM (Gemini via OpenAI-compatible API)
+def build_llm() -> ChatOpenAI:
+    return ChatOpenAI(
+        model=os.getenv("GEMINI_MODEL", "gemini-2.0-flash"),
         temperature=float(os.getenv("LLM_TEMPERATURE", "0.3")),
+        base_url="https://generativelanguage.googleapis.com/v1beta/openai/",
+        api_key=os.getenv("GOOGLE_API_KEY"),
     )
 
 

lang/agent/pyproject.toml

@@ -10,9 +10,9 @@ python = "^3.12"
 fastapi = "^0.115"
 uvicorn = "^0.34"
 langchain = "^0.3"
-langgraph = "^0.4"
+langgraph = "^0.6"
 langserve = "^0.3"
-langchain-google-genai = "^2.1"
+langchain-openai = "^0.3"
 langfuse = "^2.57"
 mcp = "^1.9"