DatabaseSessionService fails with PostgreSQL + asyncpg: can't subtract offset-naive and offset-aware datetimes

[filipecaixeta]

🔴 Required Information

Describe the Bug:
When using DatabaseSessionService with PostgreSQL and asyncpg, creating a new session fails with a DataError because timezone-aware Python datetime objects are being passed to PostgreSQL TIMESTAMP WITHOUT TIME ZONE columns.

Steps to Reproduce:

1. Configure DatabaseSessionService with a PostgreSQL database using asyncpg driver
2. Set SESSION_SERVICE_URI=postgresql+asyncpg://user:pass@localhost:5432/db
3. Create a new session via the ADK agent
4. Error occurs on session creation

Expected Behavior:
Session should be created successfully in the PostgreSQL database.

Observed Behavior:

sqlalchemy.dialects.postgresql.asyncpg.Error: <class 'asyncpg.exceptions.DataError'>: 
invalid input for query argument $5: datetime.datetime(2026, 2, 3, 21, 32, 50, 353909, 
tzinfo=datetime.timezone.utc) (can't subtract offset-naive and offset-aware datetimes)

During the INSERT:

INSERT INTO sessions (app_name, user_id, id, state, create_time, update_time) 
VALUES ($1, $2, $3, $4, $5, $6)

Environment Details:

• ADK Library Version: 1.22.1+
• Desktop OS: macOS (also affects Linux)
• Python Version: 3.13

Model Information:

• Are you using LiteLLM: N/A (issue is in session service, not model)
• Which model is being used: N/A

---

🟡 Optional Information

Regression:
Yes. This worked prior to commit 1063fa5 which changed from database-generated timestamps (func.now()) to explicit Python datetimes (datetime.now(timezone.utc)).

The SQLite case was correctly handled by stripping the timezone:

now = datetime.now(timezone.utc)
is_sqlite = self.db_engine.dialect.name == "sqlite"
if is_sqlite:
    now = now.replace(tzinfo=None)

But PostgreSQL was not handled, even though its default TIMESTAMP type is also WITHOUT TIME ZONE.

Logs:

sqlalchemy.dialects.postgresql.asyncpg.Error: <class 'asyncpg.exceptions.DataError'>: 
invalid input for query argument $5: datetime.datetime(2026, 2, 3, 21, 32, 50, 353909, 
tzinfo=datetime.timezone.utc) (can't subtract offset-naive and offset-aware datetimes)

Minimal Reproduction Code:

from google.adk.sessions import DatabaseSessionService

# Configure with PostgreSQL + asyncpg
session_service = DatabaseSessionService(
    db_url="postgresql+asyncpg://user:pass@localhost:5432/agent_sessions"
)

# This will fail when creating any session

How often has this issue occurred?:

• Always (100%) - when using PostgreSQL with asyncpg

Fix:
PR #4365 addresses this by also stripping the timezone for PostgreSQL:

is_postgres = self.db_engine.dialect.name == "postgresql"
if is_sqlite or is_postgres:
    now = now.replace(tzinfo=None)