fix(python): add missing thinking events to Event union

The Event union type was missing the following event types that are
defined as BaseEvent subclasses:
- ThinkingStartEvent
- ThinkingEndEvent
- ThinkingTextMessageStartEvent
- ThinkingTextMessageContentEvent
- ThinkingTextMessageEndEvent

This caused validation errors when using TypeAdapter[Event] to parse
events from models that emit thinking events (e.g., Claude with
extended thinking).

Also adds a test to ensure all BaseEvent subclasses are included in
the Event union, preventing similar issues in the future.

Author: thejens

sdks/python/ag_ui/core/events.py

@@ -279,11 +279,16 @@ class StepFinishedEvent(BaseEvent):
         TextMessageContentEvent,
         TextMessageEndEvent,
         TextMessageChunkEvent,
+        ThinkingTextMessageStartEvent,
+        ThinkingTextMessageContentEvent,
+        ThinkingTextMessageEndEvent,
         ToolCallStartEvent,
         ToolCallArgsEvent,
         ToolCallEndEvent,
         ToolCallChunkEvent,
         ToolCallResultEvent,
+        ThinkingStartEvent,
+        ThinkingEndEvent,
         StateSnapshotEvent,
         StateDeltaEvent,
         MessagesSnapshotEvent,

sdks/python/tests/test_events.py

@@ -1,8 +1,10 @@
 import unittest
 import json
+import typing
 from datetime import datetime
 from pydantic import ValidationError, TypeAdapter
 
+from ag_ui.core import events as events_module
 from ag_ui.core.types import Message, UserMessage, AssistantMessage, FunctionCall, ToolCall
 from ag_ui.core.events import (
     EventType,
@@ -596,6 +598,31 @@ def test_event_with_unicode_and_special_chars(self):
         # Verify Unicode and special characters are preserved
         self.assertEqual(deserialized.delta, text)
 
+    def test_all_event_subclasses_in_event_union(self):
+        """Ensure all BaseEvent subclasses are included in the Event union type"""
+
+        # Get all classes defined in the events module that are subclasses of BaseEvent
+        event_subclasses = set()
+        for name in dir(events_module):
+            obj = getattr(events_module, name)
+            if (
+                isinstance(obj, type)
+                and issubclass(obj, BaseEvent)
+                and obj is not BaseEvent
+            ):
+                event_subclasses.add(obj)
+
+        # Get all types in the Event union
+        union_types = set(typing.get_args(typing.get_args(Event)[0]))
+
+        # Check that all event subclasses are in the union
+        missing_from_union = event_subclasses - union_types
+        self.assertEqual(
+            missing_from_union,
+            set(),
+            f"The following event types are missing from the Event union: {missing_from_union}"
+        )
 
+        
 if __name__ == "__main__":
     unittest.main()