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Contribution guide.

Describe the bug
I created an application using the ADK agents, deployed on Cloud Run. I call the Cloud Run service from a Linux server using the CURL commands:

• Session creation:
  curl -X POST -H "Authorization: Bearer $TOKEN"
  $APP_URL/apps/app_agent/users/user_234/sessions/session_234
  -H "Content-Type: application/json"
  -d '{"state": {"nome_doc": "document.pdf", "tag": "1_0_0"}}'

• Agent invocation:
  curl -X POST -H "Authorization: Bearer $TOKEN"
  $APP_URL/run_sse
  -H "Content-Type: application/json"
  -d '{
  "app_name": "app_agent",
  "user_id": "user_234",
  "session_id": "session_234",
  "new_message": {
  "role": "user",
  "parts": [{
  "text": "GO!"
  }]
  },
  "streaming": false
  }'

The agent application, when attempting to read the context variables passed during session creation, cannot find them, even if both variables as present and correctly set in the STATE (see logging below).

To Reproduce

• Agent definition
  analysis_pipeline = SequentialAgent(
  name="analysis_pipeline",
  description="",
  sub_agents=[
  recognizer_doc,
  analysis_loop,
  report_composer,
  ],
  before_agent_callback=pipeline_init_context,
  )

• before_agent_callback function
  async def pipeline_init_context(callback_context: CallbackContext):
  """
  Callback function (callback_before_agent) for loading the context variables of the AGENTS.

  Args:
  callback_context: session context on which the agents will work

  Returns:
  None
  """

  logging.info(f"\n*---------------------- function pipeline_init_context")

  try:
  logging.info(f"{callback_context.state.to_dict()}")

    nome_doc = callback_context.state.get("nome_doc")
    tag = callback_context.state.get("tag")
    logging.info(f"*---------  state: nome_doc = {nome_doc}")
    logging.info(f"*---------  state: tag = {tag}")
  
    nome_doc1 = callback_context.state["nome_doc"]  # generate application error 
    tag1 = callback_context.state["tag"]
    logging.info(f"*---------  state: nome_doc = {nome_doc1}")
    logging.info(f"*---------  state: tag = {tag1}")
  
    #callback_context.state["tagmod"] = tag.replace("_", ".")
  
    logging.info(f"*---------  state: tag = {tag}")
    logging.info(f"*---------  state: tagmod = {callback_context.state["tagmod"]}")
    logging.info(f"*---------  state: nome_doc = {nome_doc}")
    .....
  

  .....
  .....
  except Exception as e:
  logging.error(f"*--------- status: error, message: No document found or loaded. {e}")
  return None

Expected behavior
Correct loading of the context variables.

Screenshots

******** OUTPUT ********
$ curl -X POST -H "Authorization: Bearer $TOKEN"
$APP_URL/apps/app_agent/users/user_234/sessions/session_234
-H "Content-Type: application/json"
-d '{"state": {"nome_doc": "document.pdf", "tag": "1_0_0"}}'

response:
{"id":"session_234","appName":"app_agent","userId":"user_234","state":{"state":{"nome_doc":"document.pdf","tag":"1_0_0"}},"events":[],"lastUpdateTime":1760876600.5299006}

$ curl -X GET -H "Authorization: Bearer $TOKEN"
$APP_URL/apps/app_agent/users/user_234/sessions/session_234

response.
{"id":"session_234","appName":"app_agent","userId":"user_234","state":{"state":{"nome_doc":"document.pdf","tag":"1_0_0"}},"events":[],"lastUpdateTime":1760876600.5299006}

$ curl -X POST -H "Authorization: Bearer $TOKEN"
$APP_URL/run_sse
-H "Content-Type: application/json"
-d '{
"app_name": "app_agent",
"user_id": "user_234",
"session_id": "session_234",
"new_message": {
"role": "user",
"parts": [{
"text": "GO!"
}]
},
"streaming": false
}'

response:
data: {"error": "'Context variable not found: nome_doc.'"}

******** Application LOG ********
*---------------------- function pipeline_init_context
*--------- {'state': {'nome_doc': 'document.pdf', 'tag': '1_0_0'}}
*--------- state: nome_doc = None
*--------- state: tag = None
*--------- pre callback_context.state["nome_doc"]
*--------- status: error, message: No document found or loaded. 'nome_doc'

Desktop (please complete the following information):

• Google ADK version: 1.5.0
• Python version: 3.12
• Framework: FastAPI with async orchestration

Model Information:

• Are you using LiteLLM: No
• Model is being used gemini-2.5-pro