test(phase6_engine): mock send_result not send (Phase 2.16, pre-empts Phase 1.3 regression)

Phase 1.3 migrated src/multi_agent_conductor.py:591 (run_worker_lifecycle)
to send_result(). The test_worker_streaming_intermediate test mocked
src.ai_client.send, which would break once Phase 1.3 was applied.
(Confirmed: test failed after Phase 1.3 commit.)

Changes:
- Replace patch(src.ai_client.send) with patch(src.ai_client.send_result)
- Rename mock_send to mock_send_result
- Wrap mock side_effect return with Result(data="DONE")
- Add "from src.result_types import Result" import

All 3 tests in test_phase6_engine.py pass.

tests/test_phase6_engine.py

@@ -2,6 +2,7 @@ from unittest.mock import MagicMock, patch
 from src.multi_agent_conductor import ConductorEngine, run_worker_lifecycle
 from src.models import Ticket, Track, WorkerContext
 from src import ai_client
+from src.result_types import Result
 
 def test_worker_streaming_intermediate():
  ticket = Ticket(id="T-001", description="Test", status="todo", assigned_to="worker")
@@ -9,7 +10,7 @@ def test_worker_streaming_intermediate():
  event_queue = MagicMock()
 
  with (
-  patch("src.ai_client.send") as mock_send, 
+  patch("src.ai_client.send_result") as mock_send_result,
   patch("src.multi_agent_conductor._queue_put") as mock_q_put,
   patch("src.multi_agent_conductor.confirm_spawn", return_value=(True, "p", "c")),
   patch("src.ai_client.reset_session"),
@@ -23,9 +24,9 @@ def test_worker_streaming_intermediate():
    if cb:
     cb({"kind": "tool_call", "payload": {"name": "test_tool", "script": "echo hello"}})
     cb({"kind": "tool_result", "payload": {"name": "test_tool", "output": "hello"}})
-   return "DONE"
+   return Result(data="DONE")
 
-  mock_send.side_effect = side_effect
+  mock_send_result.side_effect = side_effect
   run_worker_lifecycle(ticket, context, event_queue=event_queue)
 
   # _queue_put(event_queue, event_name, payload)