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Describe the bug
The version listing throws an error when a full agent engine resource name is used as an app name.
Relevant LoC:

To Reproduce
Steps to reproduce the behavior:

1. Set environment variable GOOGLE_CLOUD_AGENT_ENGINE_ID to a agent engine resource name
2. Use an agent with a tool that calls await tool_context.load_artifact(...)
3. See an error message from list_versions (called in load_artifact) that unpacks a wrong number of path elements.

Expected behavior
Loading artifacts in a tool with tool_context.load_artifact() should not fail and throw a runtime exception.

Screenshots
Not needed.

Desktop (please complete the following information):

• OS: debian
• Python version(python -V): 3.12
• ADK version(pip show google-adk): 1.6.1

Model Information:
gemini-2.5-flash

Additional context
N/A