fix: Pass state_delta to runner in /run endpoint

Merge https://github.com/google/adk-python/pull/2791

Fixes #2789

## Summary
Forward `state_delta` from the FastAPI `/run` request to `Runner.run_async(...)`, aligning behavior with the documented
API and the `/run_sse` endpoint.

## Why
The documentation for `/run` explicitly includes:
> `state_delta` (object, optional): A delta of the state to apply before the run.

However, the non‑SSE `/run` handler did not pass this value through, so `Runner.run_async` always received `None`. The
`/run_sse` path already forwarded it correctly.

## Changes
- `src/google/adk/cli/adk_web_server.py`
    - Add `state_delta=req.state_delta` to the "/run" handler’s `runner.run_async(...)` call.
- `tests/unittests/cli/test_fast_api.py`
    - Add `test_agent_run_passes_state_delta` to test the fix.

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/2791 from pguerra-ce:fix-state-delta-missing-in-run 83eec8d28b80757e24ae900285eb59530863adbd
PiperOrigin-RevId: 802703072

tests/unittests/cli/test_fast_api.py

@@ -34,6 +34,7 @@ from google.adk.evaluation.eval_result import EvalSetResult
 from google.adk.evaluation.eval_set import EvalSet
 from google.adk.evaluation.in_memory_eval_sets_manager import InMemoryEvalSetsManager
 from google.adk.events.event import Event
+from google.adk.events.event_actions import EventActions
 from google.adk.runners import Runner
 from google.adk.sessions.base_session_service import ListSessionsResponse
 from google.genai import types
@@ -94,6 +95,14 @@ def _event_3():
   )
 
 
+def _event_state_delta(state_delta: dict[str, Any]):
+  return Event(
+      author="dummy agent",
+      invocation_id="invocation_id",
+      actions=EventActions(state_delta=state_delta),
+  )
+
+
 # Define mocked async generator functions for the Runner
 async def dummy_run_live(self, session, live_request_queue):
   yield _event_1()
@@ -110,6 +119,7 @@ async def dummy_run_async(
     user_id,
     session_id,
     new_message,
+    state_delta=None,
     run_config: RunConfig = RunConfig(),
 ):
   yield _event_1()
@@ -119,6 +129,10 @@ async def dummy_run_async(
   await asyncio.sleep(0)
 
   yield _event_3()
+  await asyncio.sleep(0)
+
+  if state_delta is not None:
+    yield _event_state_delta(state_delta)
 
 
 # Define a local mock for EvalCaseResult specific to fast_api tests
@@ -744,6 +758,29 @@ def test_agent_run(test_app, create_test_session):
   logger.info("Agent run test completed successfully")
 
 
+def test_agent_run_passes_state_delta(test_app, create_test_session):
+  """Test /run forwards state_delta and surfaces it in events."""
+  info = create_test_session
+  payload = {
+      "app_name": info["app_name"],
+      "user_id": info["user_id"],
+      "session_id": info["session_id"],
+      "new_message": {"role": "user", "parts": [{"text": "Hello"}]},
+      "streaming": False,
+      "state_delta": {"k": "v", "count": 1},
+  }
+
+  # Verify the response
+  response = test_app.post("/run", json=payload)
+  assert response.status_code == 200
+  data = response.json()
+  assert isinstance(data, list)
+  assert len(data) == 4
+
+  # Verify we got the expected event
+  assert data[3]["actions"]["stateDelta"] == payload["state_delta"]
+
+
 def test_list_artifact_names(test_app, create_test_session):
   """Test listing artifact names for a session."""
   info = create_test_session