fix: extract interaction_id from SSE events for Interactions API chaining

SSE streaming events carry the interaction ID in different attributes
than the non-streaming Interaction response:
- InteractionStartEvent/CompleteEvent: event.interaction.id
- InteractionStatusUpdate: event.interaction_id

The code only checked event.id which doesn't exist on SSE event types,
so current_interaction_id was never set during streaming. This caused
_find_previous_interaction_id() to fail, breaking function calling
with StreamingMode.SSE + Interactions API.

Fixes #5169

Author: enjoykumawat

src/google/adk/models/interactions_utils.py

@@ -1013,9 +1013,18 @@ async def generate_content_via_interactions(
       # Log the streaming event
       logger.debug(build_interactions_event_log(event))
 
-      # Extract interaction ID from event if available
-      if hasattr(event, 'id') and event.id:
-        current_interaction_id = event.id
+      # Extract interaction ID from event if available.
+      # SSE events carry the ID in different attributes depending on type:
+      #   - InteractionStartEvent/CompleteEvent: event.interaction.id
+      #   - InteractionStatusUpdate: event.interaction_id
+      if (
+          hasattr(event, 'interaction')
+          and hasattr(event.interaction, 'id')
+          and event.interaction.id
+      ):
+        current_interaction_id = event.interaction.id
+      elif hasattr(event, 'interaction_id') and event.interaction_id:
+        current_interaction_id = event.interaction_id
       llm_response = convert_interaction_event_to_llm_response(
           event, aggregated_parts, current_interaction_id
       )

tests/unittests/models/test_interactions_utils.py

@@ -955,3 +955,102 @@ def test_unknown_event_type_returns_none(self):
 
     assert result is None
     assert not aggregated_parts
+
+
+class TestSSEInteractionIdExtraction:
+  """Tests for interaction_id extraction from SSE events.
+
+  SSE events carry the interaction ID in different attributes:
+  - InteractionStartEvent/CompleteEvent: event.interaction.id
+  - InteractionStatusUpdate: event.interaction_id
+  - ContentDelta/ContentStop: no interaction ID
+
+  The call_interactions_api function must extract the ID from these
+  locations so it can be propagated to LlmResponse objects and
+  ultimately stored in session events for chaining.
+  """
+
+  def test_interaction_start_event_carries_id(self):
+    """InteractionStartEvent has interaction.id — should be found."""
+    event = MagicMock()
+    event.event_type = 'interaction.start'
+    event.interaction = MagicMock()
+    event.interaction.id = 'int_start_abc'
+    # Should NOT have direct interaction_id
+    del event.interaction_id
+
+    # Verify the extraction logic matches what call_interactions_api does
+    current_id = None
+    if (
+        hasattr(event, 'interaction')
+        and hasattr(event.interaction, 'id')
+        and event.interaction.id
+    ):
+      current_id = event.interaction.id
+    elif hasattr(event, 'interaction_id') and event.interaction_id:
+      current_id = event.interaction_id
+
+    assert current_id == 'int_start_abc'
+
+  def test_status_update_event_carries_interaction_id(self):
+    """InteractionStatusUpdate has interaction_id — should be found."""
+    event = MagicMock(spec=['event_type', 'interaction_id', 'status'])
+    event.event_type = 'interaction.status_update'
+    event.interaction_id = 'int_status_xyz'
+    event.status = 'requires_action'
+
+    current_id = None
+    if (
+        hasattr(event, 'interaction')
+        and hasattr(event.interaction, 'id')
+        and event.interaction.id
+    ):
+      current_id = event.interaction.id
+    elif hasattr(event, 'interaction_id') and event.interaction_id:
+      current_id = event.interaction_id
+
+    assert current_id == 'int_status_xyz'
+
+  def test_content_delta_has_no_interaction_id(self):
+    """ContentDelta events don't carry interaction ID."""
+    event = MagicMock(spec=['event_type', 'delta', 'index', 'event_id'])
+    event.event_type = 'content.delta'
+
+    current_id = None
+    if (
+        hasattr(event, 'interaction')
+        and hasattr(event.interaction, 'id')
+        and event.interaction.id
+    ):
+      current_id = event.interaction.id
+    elif hasattr(event, 'interaction_id') and event.interaction_id:
+      current_id = event.interaction_id
+
+    assert current_id is None
+
+  def test_interaction_id_propagated_to_status_update_response(self):
+    """When interaction_id is extracted from earlier events, it should
+    be passed to convert_interaction_event_to_llm_response and appear
+    in the resulting LlmResponse for status_update events."""
+    event = MagicMock()
+    event.event_type = 'interaction.status_update'
+    event.status = 'requires_action'
+
+    # Function call was aggregated earlier
+    aggregated_parts = [
+        types.Part(
+            function_call=types.FunctionCall(
+                id='call_1', name='get_weather', args={'city': 'Tokyo'}
+            )
+        )
+    ]
+
+    # The interaction_id should have been extracted from an earlier
+    # InteractionStartEvent and passed here
+    result = interactions_utils.convert_interaction_event_to_llm_response(
+        event, aggregated_parts, interaction_id='int_from_start'
+    )
+
+    assert result is not None
+    assert result.interaction_id == 'int_from_start'
+    assert result.turn_complete is True