Documentation: load_artifacts tool appears required for PDF/HTML handling in Vertex AI Agent Engine #4928

🔴 Required Information

Describe the Bug:
When deploying an ADK agent to Vertex AI Agent Engine, uploaded artifacts such as PDF or HTML files are not processed or recognized by the agent unless the load_artifacts tool is explicitly included in the agent's tool list. This behavior differs from the artifact handling experience in the local ADK Web UI, and the necessity of including load_artifacts for Vertex AI Agent Engine deployments is not clearly documented. This creates a parity issue and can lead to confusion.

Steps to Reproduce:

1. Define an ADK agent without including load_artifacts in the tools list.
2. Deploy this agent to Vertex AI Agent Engine.
3. Attempt to interact with the deployed agent by uploading a PDF or HTML file through the Vertex AI Agent Engine interface.
4. Observe that the agent does not seem to receive or process the content of the uploaded artifact.
5. Modify the agent definition to include load_artifacts in the tools list.
6. Redeploy the updated agent to Vertex AI Agent Engine.
7. Repeat the artifact upload.
8. Observe that the agent can now access the artifact content.
   Uploading artifacts (PDFs, HTML files) to an agent deployed on Vertex AI Agent Engine should work consistently, ideally with the same ease as the ADK Web UI. If specific tools like load_artifacts are required for this functionality in the Agent Engine environment, this requirement should be clearly documented. Users might expect built-in artifact handling without needing to add a specific tool.

Expected Behavior:
Uploading artifacts (PDFs, HTML files) to an agent deployed on Vertex AI Agent Engine should work consistently, ideally with the same ease as the ADK Web UI. If specific tools like load_artifacts are required for this functionality in the Agent Engine environment, this requirement should be clearly documented. Users might expect built-in artifact handling without needing to add a specific tool.

Observed Behavior:
Artifacts are silently dropped or ignored when uploaded to an agent on Vertex AI Agent Engine if load_artifacts is not in the agent's tools. Adding the tool resolves the issue, suggesting it's necessary for this environment.

Environment Details:

• ADK Library Version (pip show google-adk):
• Desktop OS:** macOS
• Python Version (python -V):

Model Information:

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

🟡 Optional Information

Minimal Reproduction Code:

# Agent WITHOUT load_artifacts (Fails to process uploads on Agent Engine)
# root_agent_before = Agent(
# name=name,
# model=model,
# tools=[
#     # Other tools...
# ],
# instruction=instruction
# )

# Agent WITH load_artifacts (Processes uploads on Agent Engine)
root_agent_after = Agent(
    name=name,
    model=model,
    tools=[
        # ... other tools
        load_artifacts
    ],
    instruction=instruction
)

How often has this issue occurred?:
Always (100%) - When load_artifacts is not included in an agent deployed to Vertex AI Agent Engine.