fix(models): preserve interactions SSE ids for function calls

Fixes #5169 by reading interaction IDs from the actual GenAI SDK SSE event fields and carrying them through streaming function-call responses. Also adds regression coverage for interaction.complete events and streaming interaction.start chaining.

Author: kshirajahere

src/google/adk/models/interactions_utils.py

@@ -56,6 +56,29 @@
 _NEW_LINE = '\n'
 
 
+def _extract_event_id_from_interaction_event(
+    event: 'InteractionSSEEvent',
+) -> Optional[str]:
+  """Extract the SDK event identifier from an interactions SSE event."""
+  return getattr(event, 'event_id', None) or getattr(event, 'id', None)
+
+
+def _extract_interaction_id_from_event(
+    event: 'InteractionSSEEvent',
+) -> Optional[str]:
+  """Extract the interaction chain identifier from an SSE event."""
+  interaction = getattr(event, 'interaction', None)
+  if interaction and getattr(interaction, 'id', None):
+    return interaction.id
+
+  interaction_id = getattr(event, 'interaction_id', None)
+  if interaction_id:
+    return interaction_id
+
+  # Fall back to legacy field names when older SDK shapes are in play.
+  return getattr(event, 'id', None)
+
+
 def convert_part_to_interaction_content(part: types.Part) -> Optional[dict]:
   """Convert a types.Part to an interaction content dict.
 
@@ -487,6 +510,7 @@ def convert_interaction_event_to_llm_response(
   from .llm_response import LlmResponse
 
   event_type = getattr(event, 'event_type', None)
+  interaction_id = interaction_id or _extract_interaction_id_from_event(event)
 
   if event_type == 'content.delta':
     delta = event.delta
@@ -565,9 +589,10 @@ def convert_interaction_event_to_llm_response(
           interaction_id=interaction_id,
       )
 
-  elif event_type == 'interaction':
-    # Final interaction event with complete data
-    return convert_interaction_to_llm_response(event)
+  elif event_type in ('interaction.complete', 'interaction'):
+    # Final interaction event with complete data.
+    interaction = getattr(event, 'interaction', event)
+    return convert_interaction_to_llm_response(interaction)
 
   elif event_type == 'interaction.status_update':
     status = getattr(event, 'status', None)
@@ -834,7 +859,7 @@ def build_interactions_event_log(event: InteractionSSEEvent) -> str:
     A formatted log string describing the event.
   """
   event_type = getattr(event, 'event_type', 'unknown')
-  event_id = getattr(event, 'id', None)
+  event_id = _extract_event_id_from_interaction_event(event)
 
   details = []
 
@@ -1014,8 +1039,9 @@ async def generate_content_via_interactions(
       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
+      current_interaction_id = (
+          _extract_interaction_id_from_event(event) or current_interaction_id
+      )
       llm_response = convert_interaction_event_to_llm_response(
           event, aggregated_parts, current_interaction_id
       )

tests/unittests/models/test_interactions_utils.py

@@ -16,11 +16,36 @@
 
 import base64
 import json
+from unittest.mock import AsyncMock
 from unittest.mock import MagicMock
 
 from google.adk.models import interactions_utils
 from google.adk.models.llm_request import LlmRequest
 from google.genai import types
+from google.genai._interactions.types import ContentDelta
+from google.genai._interactions.types import ContentStop
+from google.genai._interactions.types import Interaction
+from google.genai._interactions.types import InteractionCompleteEvent
+from google.genai._interactions.types import InteractionStartEvent
+from google.genai._interactions.types import InteractionStatusUpdate
+from google.genai._interactions.types.content_delta import DeltaFunctionCall
+import pytest
+
+
+class _MockAsyncIterator:
+  """Simple async iterator for streaming test events."""
+
+  def __init__(self, values):
+    self._iterator = iter(values)
+
+  def __aiter__(self):
+    return self
+
+  async def __anext__(self):
+    try:
+      return next(self._iterator)
+    except StopIteration as exc:
+      raise StopAsyncIteration from exc
 
 
 class TestConvertPartToInteractionContent:
@@ -955,3 +980,100 @@ def test_unknown_event_type_returns_none(self):
 
     assert result is None
     assert not aggregated_parts
+
+  def test_interaction_complete_event(self):
+    """Test converting an interaction.complete event."""
+    interaction = Interaction(
+        id='int_complete',
+        created='2026-04-07T00:00:00Z',
+        updated='2026-04-07T00:00:01Z',
+        status='completed',
+        outputs=[{'type': 'text', 'text': 'Done'}],
+    )
+    event = InteractionCompleteEvent(
+        event_type='interaction.complete',
+        interaction=interaction,
+    )
+
+    result = interactions_utils.convert_interaction_event_to_llm_response(
+        event, aggregated_parts=[]
+    )
+
+    assert result is not None
+    assert result.interaction_id == 'int_complete'
+    assert result.content.parts[0].text == 'Done'
+    assert result.turn_complete is True
+
+
+class TestGenerateContentViaInteractions:
+  """Tests for generate_content_via_interactions."""
+
+  @pytest.mark.asyncio
+  async def test_stream_uses_interaction_start_id_for_function_calls(self):
+    """Test that streaming function calls retain the interaction chain ID."""
+    interaction = Interaction(
+        id='int_stream_123',
+        created='2026-04-07T00:00:00Z',
+        updated='2026-04-07T00:00:01Z',
+        status='requires_action',
+    )
+    stream_events = [
+        InteractionStartEvent(
+            event_type='interaction.start',
+            interaction=interaction,
+        ),
+        ContentDelta(
+            event_type='content.delta',
+            index=0,
+            delta=DeltaFunctionCall(
+                type='function_call',
+                id='fc_123',
+                name='get_weather',
+                arguments={'city': 'Tokyo'},
+            ),
+        ),
+        ContentStop(event_type='content.stop', index=0),
+        InteractionStatusUpdate(
+            event_type='interaction.status_update',
+            interaction_id='int_stream_123',
+            status='requires_action',
+        ),
+    ]
+    api_client = MagicMock()
+    api_client.aio.interactions.create = AsyncMock(
+        return_value=_MockAsyncIterator(stream_events)
+    )
+    llm_request = LlmRequest(
+        model='gemini-2.5-flash',
+        contents=[
+            types.Content(
+                role='user',
+                parts=[types.Part.from_text(text='Weather in Tokyo?')],
+            )
+        ],
+        config=types.GenerateContentConfig(),
+    )
+
+    responses = [
+        response
+        async for response in (
+            interactions_utils.generate_content_via_interactions(
+                api_client=api_client,
+                llm_request=llm_request,
+                stream=True,
+            )
+        )
+    ]
+
+    function_call_response = next(
+        response
+        for response in responses
+        if response.content
+        and response.content.parts
+        and response.content.parts[0].function_call
+    )
+
+    assert function_call_response.interaction_id == 'int_stream_123'
+    assert function_call_response.content.parts[0].function_call.name == (
+        'get_weather'
+    )