google-adk[db] is missing greenlet

[aseelmannfuzzy]

🔴 Required Information

Describe the Bug:
With the recent new release of sqlalchemy (v2.1), sqlalchemy does no longer install the greenlet dependency by default. Consequently, with only google-adk[db] and an install after the release of sqlalchemy in v2.1, the db-related async functionality is missing and instantiating DatabaseSessionService results in NameError: name 'create_async_engine' is not defined.

Steps to Reproduce:

1. Install 'google-adk[db]' (tested with v2.10.0); this needs to install sqlalchemy>=2.1
2. Instantiate a DatabaseSessionService
3. Observe the error

db_engine = create_async_engine(db_url, **engine_kwargs)
                      ^^^^^^^^^^^^^^^^^^^
E         NameError: name 'create_async_engine' is not defined

.venv/lib/python3.13/site-packages/google/adk/sessions/database_session_service.py:393: NameError

Expected Behavior:
Instantiating DatabaseSessionService should pass normally.

Observed Behavior:
A NameError occurs due to the missing greenlet dependency.

Environment Details:

• ADK Library Version (pip show google-adk): 2.10.0 (but earlier version should be affected alike)
• Desktop OS:** Ubuntu 24.04 on WSL under Windows 11
• Python Version (python -V): 3.13.13

Model Information:

• Are you using LiteLLM: No
• Which model is being used: gemini-3.7-flash

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🟡 Optional Information

Regression:
This worked fine with ~v2.0 of sqlalchemy.

Additional Context:
Additionally installing greenlet (resp. sqlalchemy[asyncio]) solves the issue, but since ADK relies on async session so heavily, google-adk[db] really just should install sqlalchemy with the asyncio extra.