fix(a2a): render HITL interrupt when prompt is in a data part

A2A input/auth-required prompts sent as a DataPart became an opaque
inline_data JSON blob, so no HITL function call was produced and the
client rendered nothing.

Extract the prompt from the data part so these tasks surface a
proper HITL function call. Adds unit tests.

PiperOrigin-RevId: 933586203

Author: google-genai-bot

src/google/adk/a2a/converters/to_adk_event.py

@@ -35,7 +35,10 @@
 from ...events.event import Event
 from ...events.event_actions import EventActions
 from ..experimental import a2a_experimental
+from .part_converter import A2A_DATA_PART_END_TAG
 from .part_converter import A2A_DATA_PART_METADATA_IS_LONG_RUNNING_KEY
+from .part_converter import A2A_DATA_PART_START_TAG
+from .part_converter import A2A_DATA_PART_TEXT_MIME_TYPE
 from .part_converter import A2APartToGenAIPartConverter
 from .part_converter import convert_a2a_part_to_genai_part
 from .utils import _get_adk_metadata_key
@@ -283,6 +286,40 @@ def _merge_event_actions(
   return EventActions.model_validate(merged_actions_data)
 
 
+def _extract_user_input_prompt(part: genai_types.Part) -> Any:
+  """Extracts a prompt from a converted ADK part."""
+  if part.text:
+    return part.text
+
+  blob = part.inline_data
+  if (
+      blob is None
+      or blob.data is None
+      or blob.mime_type != A2A_DATA_PART_TEXT_MIME_TYPE
+      or not blob.data.startswith(A2A_DATA_PART_START_TAG)
+      or not blob.data.endswith(A2A_DATA_PART_END_TAG)
+  ):
+    return None
+
+  raw_json = blob.data[
+      len(A2A_DATA_PART_START_TAG) : -len(A2A_DATA_PART_END_TAG)
+  ]
+  try:
+    data_part = json.loads(raw_json)
+  except (ValueError, TypeError) as e:
+    logger.warning("Failed to parse A2A data part JSON for HITL prompt: %s", e)
+    return None
+
+  if not isinstance(data_part, dict):
+    logger.warning(
+        "Unexpected A2A data part JSON of type %s for HITL prompt",
+        type(data_part).__name__,
+    )
+    return None
+
+  return data_part.get("data")
+
+
 def _create_mock_function_call_for_required_user_input(
     state: TaskState,
     output_parts: list[genai_types.Part],
@@ -308,15 +345,16 @@ def _create_mock_function_call_for_required_user_input(
   else:
     return output_parts, long_running_function_ids
 
-  # Find the last text part from the bottom to replace it with a function call.
-  # In case of input-required / auth-required events, the LLM should stop the
-  # production of other parts.
+  # Find the last part with a usable prompt from the bottom to replace it with a
+  # function call. In case of input-required / auth-required events, the LLM
+  # should stop the production of other parts.
   for i in range(len(output_parts) - 1, -1, -1):
-    if output_parts[i].text:
+    prompt = _extract_user_input_prompt(output_parts[i])
+    if prompt:
       function_call = genai_types.FunctionCall(
           id=str(uuid.uuid4()),
           name=function_name,
-          args={args_key: output_parts[i].text},
+          args={args_key: prompt},
       )
       long_running_function_ids = set()
       long_running_function_ids.add(function_call.id)

tests/unittests/a2a/converters/test_to_adk.py

@@ -14,6 +14,7 @@
 
 from __future__ import annotations
 
+import json
 from unittest.mock import Mock
 
 from a2a.types import Artifact
@@ -25,7 +26,10 @@
 from a2a.types import TaskStatus
 from a2a.types import TaskStatusUpdateEvent
 from a2a.types import TextPart
+from google.adk.a2a.converters.part_converter import A2A_DATA_PART_END_TAG
 from google.adk.a2a.converters.part_converter import A2A_DATA_PART_METADATA_IS_LONG_RUNNING_KEY
+from google.adk.a2a.converters.part_converter import A2A_DATA_PART_START_TAG
+from google.adk.a2a.converters.part_converter import A2A_DATA_PART_TEXT_MIME_TYPE
 from google.adk.a2a.converters.to_adk_event import convert_a2a_artifact_update_to_event
 from google.adk.a2a.converters.to_adk_event import convert_a2a_message_to_event
 from google.adk.a2a.converters.to_adk_event import convert_a2a_status_update_to_event
@@ -465,6 +469,99 @@ def test_convert_a2a_task_to_event_no_text_parts(self):
     assert event.content is not None
     assert event.content.parts == [mock_image_part]
 
+  def test_convert_a2a_task_to_event_data_part_input_required(self):
+    """Input-required prompt carried in a data part becomes a function call."""
+    part1 = Mock(spec=A2APart)
+    part1.root = Mock()  # Not a TextPart.
+    part1.root.metadata = {}
+
+    task = Task(
+        id="task-1",
+        context_id="context-1",
+        kind="task",
+        status=TaskStatus(
+            state=TaskState.input_required,
+            timestamp="now",
+            message=Message(
+                message_id="m1",
+                role="agent",
+                parts=[part1],
+            ),
+        ),
+    )
+
+    prompt = {
+        "id": "abc123",
+        "text": "Please confirm this action. Do you want to continue?",
+    }
+    data_part_json = json.dumps({"data": prompt, "kind": "data"}).encode(
+        "utf-8"
+    )
+    mock_data_blob_part = genai_types.Part(
+        inline_data=genai_types.Blob(
+            mime_type=A2A_DATA_PART_TEXT_MIME_TYPE,
+            data=A2A_DATA_PART_START_TAG
+            + data_part_json
+            + A2A_DATA_PART_END_TAG,
+        )
+    )
+
+    event = convert_a2a_task_to_event(
+        task,
+        author="test-author",
+        invocation_context=self.mock_context,
+        part_converter=Mock(return_value=[mock_data_blob_part]),
+    )
+
+    assert event is not None
+    assert event.content is not None
+    assert (
+        event.content.parts[0].function_call.name
+        == MOCK_FUNCTION_CALL_FOR_REQUIRED_USER_INPUT
+    )
+    assert event.content.parts[0].function_call.args["input_required"] == prompt
+    assert event.long_running_tool_ids
+
+  def test_convert_a2a_task_to_event_data_part_malformed_json(self):
+    """A malformed data-part blob is left untouched (no crash, no fc)."""
+    part1 = Mock(spec=A2APart)
+    part1.root = Mock()  # Not a TextPart.
+    part1.root.metadata = {}
+
+    task = Task(
+        id="task-1",
+        context_id="context-1",
+        kind="task",
+        status=TaskStatus(
+            state=TaskState.input_required,
+            timestamp="now",
+            message=Message(
+                message_id="m1",
+                role="agent",
+                parts=[part1],
+            ),
+        ),
+    )
+
+    mock_bad_blob_part = genai_types.Part(
+        inline_data=genai_types.Blob(
+            mime_type=A2A_DATA_PART_TEXT_MIME_TYPE,
+            data=A2A_DATA_PART_START_TAG + b"not-json" + A2A_DATA_PART_END_TAG,
+        )
+    )
+
+    event = convert_a2a_task_to_event(
+        task,
+        author="test-author",
+        invocation_context=self.mock_context,
+        part_converter=Mock(return_value=[mock_bad_blob_part]),
+    )
+
+    assert event is not None
+    assert event.content is not None
+    assert event.content.parts == [mock_bad_blob_part]
+    assert not event.long_running_tool_ids
+
   def test_convert_a2a_status_update_to_event_success(self):
     """Test successful conversion of A2A status update to Event."""
     a2a_part = Mock(spec=A2APart)