diff --git a/openhands/controller/agent_controller.py b/openhands/controller/agent_controller.py
index d4fd9178b390..f2682a3da16a 100644
--- a/openhands/controller/agent_controller.py
+++ b/openhands/controller/agent_controller.py
@@ -983,10 +983,12 @@ def _is_stuck(self) -> bool:
 
     def __repr__(self):
         return (
-            f'AgentController(id={self.id}, agent={self.agent!r}, '
-            f'event_stream={self.event_stream!r}, '
-            f'state={self.state!r}, '
-            f'delegate={self.delegate!r}, _pending_action={self._pending_action!r})'
+            f'AgentController(id={getattr(self, "id", "<uninitialized>")}, '
+            f'agent={getattr(self, "agent", "<uninitialized>")!r}, '
+            f'event_stream={getattr(self, "event_stream", "<uninitialized>")!r}, '
+            f'state={getattr(self, "state", "<uninitialized>")!r}, '
+            f'delegate={getattr(self, "delegate", "<uninitialized>")!r}, '
+            f'_pending_action={getattr(self, "_pending_action", "<uninitialized>")!r})'
         )
 
     def _is_awaiting_observation(self):
diff --git a/tests/unit/test_agent_session.py b/tests/unit/test_agent_session.py
new file mode 100644
index 000000000000..2619c7949804
--- /dev/null
+++ b/tests/unit/test_agent_session.py
@@ -0,0 +1,98 @@
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from openhands.controller.agent import Agent
+from openhands.controller.agent_controller import AgentController
+from openhands.core.config import AppConfig, LLMConfig
+from openhands.events import EventStream, EventStreamSubscriber
+from openhands.llm import LLM
+from openhands.llm.metrics import Metrics
+from openhands.runtime.base import Runtime
+from openhands.server.session.agent_session import AgentSession
+from openhands.storage.memory import InMemoryFileStore
+
+
+@pytest.fixture
+def mock_agent():
+    """Create a properly configured mock agent with all required nested attributes"""
+    # Create the base mocks
+    agent = MagicMock(spec=Agent)
+    llm = MagicMock(spec=LLM)
+    metrics = MagicMock(spec=Metrics)
+    llm_config = MagicMock(spec=LLMConfig)
+
+    # Configure the LLM config
+    llm_config.model = 'test-model'
+    llm_config.base_url = 'http://test'
+    llm_config.draft_editor = None
+    llm_config.max_message_chars = 1000
+
+    # Set up the chain of mocks
+    llm.metrics = metrics
+    llm.config = llm_config
+    agent.llm = llm
+    agent.name = 'test-agent'
+    agent.sandbox_plugins = []
+
+    return agent
+
+
+@pytest.mark.asyncio
+async def test_agent_session_start_calls_set_initial_state_once(mock_agent):
+    """Test that AgentSession.start() only calls set_initial_state once during controller initialization"""
+
+    # Setup
+    file_store = InMemoryFileStore({})
+    session = AgentSession(sid='test-session', file_store=file_store)
+
+    # Create a mock runtime and set it up
+    mock_runtime = MagicMock(spec=Runtime)
+
+    # Mock the runtime creation to set up the runtime attribute
+    async def mock_create_runtime(*args, **kwargs):
+        session.runtime = mock_runtime
+
+    session._create_runtime = AsyncMock(side_effect=mock_create_runtime)
+
+    # Create a mock EventStream
+    mock_event_stream = MagicMock(spec=EventStream)
+    mock_event_stream.get_events.return_value = []
+    mock_event_stream.get_latest_event_id.return_value = 0
+    mock_event_stream.subscribe = MagicMock()
+
+    # Inject the mock event stream into the session
+    session.event_stream = mock_event_stream
+
+    # Create a spy on set_initial_state by subclassing AgentController
+    class SpyAgentController(AgentController):
+        set_initial_state_call_count = 0
+
+        def set_initial_state(self, *args, **kwargs):
+            self.set_initial_state_call_count += 1
+            super().set_initial_state(*args, **kwargs)
+
+    # Patch AgentController with our spy version and inject our mock event stream
+    with patch(
+        'openhands.server.session.agent_session.AgentController', SpyAgentController
+    ), patch(
+        'openhands.server.session.agent_session.EventStream',
+        return_value=mock_event_stream,
+    ):
+        # Start the session
+        await session.start(
+            runtime_name='test-runtime',
+            config=AppConfig(),
+            agent=mock_agent,
+            max_iterations=10,
+        )
+
+        # Verify set_initial_state was called exactly once
+        assert session.controller.set_initial_state_call_count == 1
+
+        # Verify EventStream.subscribe was called with correct parameters
+        mock_event_stream.subscribe.assert_called_with(
+            EventStreamSubscriber.AGENT_CONTROLLER,
+            session.controller.on_event,
+            session.controller.id,
+        )