fix(quickstart): robust tool lookup and modernize dependencies in Python samples (googleapis#2863)

## Description
This PR addresses several reliability and modernization issues in the
Python quickstart samples and documentation:

* Replaced brittle hardcoded index-based tool lookups
(`toolbox_tools[0]`) with a robust name-based lookup dictionary
(`tool_map`) in `core/quickstart.py` and `local_quickstart.md`.
* This prevents `TypeError` failures when the tool order returned by the
server changes.
* Implemented modernization & model updates.
* Updated models to use `gemini-2.5-flash` across Core, LangChain, and
LlamaIndex quickstarts.
* Updated `toolbox-core` and `toolbox-langchain` dependencies to
`1.0.0`.
* Switched the LangChain sample from `ChatVertexAI` to
`ChatGoogleGenerativeAI` and updated `langgraph` to `1.1.6` to resolve
dependency conflicts in the CI environment.
* Updated a test query in `adk/agent.py` to directly call `update-hotel`
instead of asking for a complex multi-action "Book with dates" request
in one shot, which was causing model execution failures.

Author: anubhav756

docs/en/documentation/configuration/pre-post-processing/python/adk/agent.py

@@ -128,7 +128,7 @@ async def main():
         runner,
         session_id,
         user_id,
-        "Book a hotel with id 5 with checkin date 2025-01-18 and checkout date 2025-02-10",
+        "Update hotel with id 5 with checkin date 2025-01-18 and checkout date 2025-02-10",
     )
     await toolset.close()
 

docs/en/documentation/configuration/pre-post-processing/python/adk/requirements.txt

@@ -1,3 +1,2 @@
-google-adk[toolbox]==1.27.2
-toolbox-adk==0.7.0
-google-genai==1.67.0
+google-adk[toolbox]==1.28.1
+google-genai==1.67.0

docs/en/documentation/configuration/pre-post-processing/python/langchain/agent.py

@@ -4,7 +4,7 @@
 from langchain.agents import create_agent
 from langchain.agents.middleware import wrap_tool_call
 from langchain_core.messages import ToolMessage
-from langchain_google_vertexai import ChatVertexAI
+from langchain_google_genai import ChatGoogleGenerativeAI
 from toolbox_langchain import ToolboxClient
 
 system_prompt = """
@@ -84,7 +84,7 @@ async def enrich_response(request, handler):
 async def main():
     async with ToolboxClient("http://127.0.0.1:5000") as client:
         tools = await client.aload_toolset("my-toolset")
-        model = ChatVertexAI(model="gemini-2.5-flash")
+        model = ChatGoogleGenerativeAI(model="gemini-2.5-flash")
         agent = create_agent(
             system_prompt=system_prompt,
             model=model,
@@ -94,22 +94,24 @@ async def main():
         )
         # Test post-processing
         user_input = "Book hotel with id 3."
+        print(f"\n[INPUT] User: {user_input}")
         response = await agent.ainvoke(
             {"messages": [{"role": "user", "content": user_input}]}
         )
 
         print("-" * 50)
         last_ai_msg = response["messages"][-1].content
-        print(f"AI: {last_ai_msg}")
+        print(f"[OUTPUT] AI: {last_ai_msg}")
 
         # Test Pre-processing
         print("-" * 50)
         user_input = "Update my hotel with id 3 with checkin date 2025-01-18 and checkout date 2025-02-20."
+        print(f"\n[INPUT] User: {user_input}")
         response = await agent.ainvoke(
             {"messages": [{"role": "user", "content": user_input}]}
         )
         last_ai_msg = response["messages"][-1].content
-        print(f"AI: {last_ai_msg}")
+        print(f"[OUTPUT] AI: {last_ai_msg}")
 
 
 if __name__ == "__main__":

docs/en/documentation/configuration/pre-post-processing/python/langchain/requirements.txt

@@ -1,3 +1,3 @@
 langchain==1.2.12
-langchain-google-vertexai==3.2.2
-toolbox-langchain==0.6.0
+langchain-google-genai==4.2.1
+toolbox-langchain==1.0.0