chore(python-sdk): literal defaults

[stevenh]

Set the event type and message role using pydantic Field and disable setting in the constructor to help prevent accidental misuse while reducing unnecessary boilerplate code.

Replace Role type alias with an Enum to eliminate repeating string literals and align with EventType.

Use Field(min_length=1) to validate TextMessageContentEvent delta, simplifying the code.

Fixes #41

[Copilot]

Pull Request Overview

This PR refactors the SDK to enforce literal defaults for event types and message roles using pydantic Fields with init=False, reducing boilerplate and minimizing misuse. Key changes include:

• Removing explicit specification of role and type in message/event constructors.
• Replacing Role type alias with a Role Enum.
• Adding Field(min_length=1) validation for TextMessageContentEvent delta.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
python-sdk/tests/test_types.py	Removed redundant role entries from tests for message serialization
python-sdk/tests/test_events.py	Removed explicit type and role fields from event tests
python-sdk/tests/test_encoder.py	Removed explicit type field in event creation for encoding tests
python-sdk/ag_ui/core/types.py	Updated message role definitions to use the Role Enum and Field with init=False
python-sdk/ag_ui/core/events.py	Updated event type definitions to use Field with literal defaults and init=False

Comments suppressed due to low confidence (1)

python-sdk/tests/test_events.py:367

• With the use of Field(min_length=1) for the 'delta' field, pydantic now raises a ValidationError instead of a ValueError when an empty string is provided. Update the test in test_validation_constraints to expect ValidationError instead of ValueError.

TextMessageContentEvent(