fix: Prevent flight rebooking by adding booking confirmation message (#549)

This PR addresses an issue where the agent could attempt to rebook a
flight immediately after a successful booking.

## Problem
Previously, after the `insert_ticket` tool successfully executed, a
confirmation message was not added to the agent's conversation history
from our custom node. This lack of explicit confirmation left the agent
without the necessary context to know the booking was complete. As a
result, the agent could incorrectly infer that the booking task had
failed and attempt to perform the booking again.

## Solution
This PR modifies the custom node to add a success message to the agent's
conversation history immediately after the `insert_ticket` tool
completes successfully. This message explicitly confirms that the flight
has been booked, providing the agent with the proper context to conclude
the booking process and not attempt a rebooking.

This PR also makes the booking success/decline messages consistent
between LangGraph and UI chat history. This is so that after a page
refresh, the messages remains consistent on the Chat UI.

Author: anubhav756

agent/react_graph.py

@@ -19,6 +19,7 @@
 from langchain_core.messages import (
     AIMessage,
     BaseMessage,
+    HumanMessage,
     ToolCall,
 )
 from langchain_core.prompts.chat import ChatPromptTemplate
@@ -164,7 +165,16 @@ async def insert_ticket_node(state: UserState):
         if hasattr(last_message, "tool_calls") and len(last_message.tool_calls) > 0:
             tool_call = last_message.tool_calls[0]
             tool_args = tool_call.get("args")
-            await insert_ticket.ainvoke(tool_args)
+            output = await insert_ticket.ainvoke(tool_args)
+            human_message = HumanMessage(content="Looks good to me.")
+            ai_message = AIMessage(
+                content=(
+                    "Your flight has been successfully booked."
+                    if output == "null"
+                    else output
+                )
+            )
+            return {"messages": [human_message, ai_message]}
 
     # Define constant node strings
     AGENT_NODE = "agent"

app.py

@@ -181,7 +181,7 @@ async def book_flight(request: Request, params: str = Body(embed=True)):
     response = await agent.user_session_insert_ticket(request.session["uuid"], params)
     # Note in the history, that the ticket has been successfully booked
     request.session["history"].append(
-        {"type": "ai", "data": {"content": "I have booked your ticket."}}
+        {"type": "ai", "data": {"content": "Your flight has been successfully booked."}}
     )
     return response
 
@@ -198,7 +198,10 @@ async def decline_flight(request: Request):
         {"type": "ai", "data": {"content": "Please confirm if you would like to book."}}
     )
     request.session["history"].append(
-        {"type": "human", "data": {"content": "I changed my mind."}}
+        {
+            "type": "human",
+            "data": {"content": "I changed my mind. Decline ticket booking."},
+        }
     )
     request.session["history"].append({"type": "ai", "data": {"content": response}})
     return response