Missing injected prompt in conversation context, prompt injected using before_model_callback method #3138
Description
Describe the bug
Extra prompt injection is implemented using before_model_callback method. However, this prompt injection will disappear whenever user giving new input to the LlmAgent.
For example:
# At t=0
==New Input==
-> User input: Hi
-> Before model callback: Ignore this user input: Index=0
-> Model response: Hi, how can I help you
# At t=1
==Conversation context==
-> User input: Hi
-> Model response: Hi, how can I help you?
==New Input==
-> User input: How are you?
-> Before model callback: Ignore this user input: Index=1`
-> Model response: I am fine. How about you?
As you can see, the injected prompt("Ignore this user input: Index=0") by before_model_callback at t=0 is missing in the conversation context at t=1.
To Reproduce
Put this before_model_callback to LlmAgent
from google.adk.agents.callback_context import CallbackContext
from google.adk.models import LlmRequest, LlmResponse
from google.genai import types
index = 0
def before_model_callback(callback_context: CallbackContext, llm_request: LlmRequest) -> LlmRequest | None:
"""Inspects/modifies the callback context and LLM request before it's sent.
Args:
callback_context (CallbackContext): Model callback context.
llm_request (LlmRequest): LLM request.
"""
global index
curr_context = callback_context.state.to_dict()
logger.info(f"[Before Model callback] Current context: {curr_context}")
llm_request.contents.append(
types.Content(role="user", parts=[types.Part(text=f"Ignore this user input: Index={index}")])
)
index += 1
returnExpected behavior
The prompt inserted by before_model_callback should remain accessible within the conversation context at any point in time.
Screenshots
t=0
t=1
Desktop (please complete the following information):
- OS: [e.g. macOS, Linux, Windows]: macOS
- Python version(python -V): 3.11.8
- ADK version(pip show google-adk): 1.15.1
Model Information:
- Are you using LiteLLM: Yes
- Which model is being used: gpt-4o