update_media_buy fails with timezone mismatch error when updating dates

[estofko-scope3]

When calling update_media_buy with start_time or end_time, the operation fails with:

can't subtract offset-naive and offset-aware datetimes

This occurs because the code mixes timezone-aware datetimes (from request parsing) with potentially timezone-naive datetimes (from database).

Symptoms:

{
  "success": false,
  "status": "completed", 
  "error": "A2A agent returned error: Unable to update media buy: can't subtract offset-naive and offset-aware datetimes"
}

When updating only end_time:

• start_dt = media_buy.start_time from database (possibly naive)
• end_dt = parsed from request with timezone (aware)
• Subtraction fails

[KonstantinMirin]

The likely reason is... that DB doesn't store timezone information. See src/core/database/models.py:812-815

    start_date: Mapped[Date] = mapped_column(Date, nullable=False)
    end_date: Mapped[Date] = mapped_column(Date, nullable=False)
    start_time: Mapped[datetime | None] = mapped_column(DateTime, nullable=True)
    end_time: Mapped[datetime | None] = mapped_column(DateTime, nullable=True)

None of them has timezone information; it is silently dropped.

Also, I am not sure what the reason is to have both start/end time and start/end date; the AdCP request sends a full string with time and timezone.

[KonstantinMirin]

I'll take care of this as a part of my model migration (elimination of model_dump() problematic pattern).

The solution is to use Timezone-aware DateTime for every field - both internal for the Salesagent and external from AdCP library (which is timezone-aware for all fields)

The edge case is "asap" for starting date which would be converted to "now" with endtime's timezone information (I actually don't like that part of the protocol -- too many questions about the implementation, so that's my take as the protocol doesn't define it)

[KonstantinMirin]

Addressed here: https://github.com/KonstantinMirin/prebid-salesagent/tree/KonstantinMirin/refactoring-adcp-client-model-inheritance

Some more work is needed there to finish the model cleanup to the "presentable" state. Feel free to cherry-pick the migration and model changes (dc04c47)

[KonstantinMirin]

Should be fixed after #1051 merge, need to confirm or close

[KonstantinMirin]

Fixed in adcp v3.6 migration branch. Defense-in-depth fix:

1. Migration 3a16c5fc27ce: all datetime columns migrated from TIMESTAMP to TIMESTAMPTZ
2. DB model: DateTime(timezone=True) ensures PostgreSQL returns aware datetimes
3. Schema validation: UpdateMediaBuyRequest rejects naive datetimes at the boundary
4. Regression tests added: TestTimezoneHandlingRegression (4 tests) in test_update_media_buy_behavioral.py