diff --git a/haiku_rag_slim/haiku/rag/agents/chat/state.py b/haiku_rag_slim/haiku/rag/agents/chat/state.py
index 84d30204..d8ef026a 100644
--- a/haiku_rag_slim/haiku/rag/agents/chat/state.py
+++ b/haiku_rag_slim/haiku/rag/agents/chat/state.py
@@ -1,4 +1,3 @@
-import uuid
 from dataclasses import dataclass, field
 from datetime import datetime
 from typing import Any
@@ -75,7 +74,7 @@ class SessionContext(BaseModel):
 class ChatSessionState(BaseModel):
     """State shared between frontend and agent via AG-UI."""
 
-    session_id: str = Field(default_factory=lambda: str(uuid.uuid4()))
+    session_id: str = ""
     initial_context: str | None = None
     citations: list[Citation] = []
     qa_history: list[QAResponse] = []
diff --git a/tests/agents/chat/test_state.py b/tests/agents/chat/test_state.py
index 2cf557a1..30ace7ab 100644
--- a/tests/agents/chat/test_state.py
+++ b/tests/agents/chat/test_state.py
@@ -1,5 +1,3 @@
-import uuid
-
 from ag_ui.core import StateDeltaEvent
 
 from haiku.rag.agents.chat.state import (
@@ -578,13 +576,14 @@ def test_chat_deps_state_getter_includes_document_filter():
     assert state[AGUI_STATE_KEY]["document_filter"] == ["doc1.pdf", "doc2.pdf"]
 
 
-def test_chat_session_state_auto_generates_session_id():
-    """New ChatSessionState should have a valid UUID session_id."""
+def test_chat_session_state_defaults_to_empty_session_id():
+    """New ChatSessionState should default to empty session_id.
+
+    Tools in agent.py detect the empty string and assign a UUID,
+    which then appears in the state delta so clients receive it.
+    """
     state = ChatSessionState()
-    assert state.session_id
-    assert len(state.session_id) == 36  # UUID format
-    # Verify it's a valid UUID
-    uuid.UUID(state.session_id)
+    assert state.session_id == ""
 
 
 def test_chat_session_state_preserves_explicit_session_id():
@@ -593,13 +592,6 @@ def test_chat_session_state_preserves_explicit_session_id():
     assert state.session_id == "my-custom-id"
 
 
-def test_chat_session_state_each_instance_gets_unique_id():
-    """Each new instance should get a unique session_id."""
-    state1 = ChatSessionState()
-    state2 = ChatSessionState()
-    assert state1.session_id != state2.session_id
-
-
 def test_chat_session_state_initial_context_default_none():
     """Initial context should default to None."""
     state = ChatSessionState()
@@ -650,6 +642,27 @@ def test_chat_session_state_model_dump_json_serializes_datetime():
     assert snapshot["session_context"]["last_updated"] == "2025-01-27T12:00:00"
 
 
+def test_emit_state_event_includes_session_id_when_assigned():
+    """emit_state_event detects session_id change from empty to UUID.
+
+    When session_id defaults to "" and the tool assigns a UUID,
+    the delta must include session_id so clients can persist it.
+    """
+    from haiku.rag.agents.chat.state import emit_state_event
+
+    current_state = ChatSessionState()  # session_id=""
+    new_state = ChatSessionState(session_id="assigned-uuid-123")
+
+    event = emit_state_event(current_state, new_state)
+
+    assert event is not None
+    session_id_op = next(
+        (op for op in event.delta if op["path"] == "/session_id"), None
+    )
+    assert session_id_op is not None
+    assert session_id_op["value"] == "assigned-uuid-123"
+
+
 def test_emit_state_event_returns_none_when_no_changes():
     """emit_state_event returns None when states are identical."""
     from haiku.rag.agents.chat.state import emit_state_event
diff --git a/tests/chat/test_chat_app.py b/tests/chat/test_chat_app.py
index 4313fba1..f7b24142 100644
--- a/tests/chat/test_chat_app.py
+++ b/tests/chat/test_chat_app.py
@@ -266,9 +266,9 @@ async def test_clear_chat_resets_session(temp_db_path: Path):
             await chat_history.add_message("assistant", "Hi there")
             assert len(chat_history.messages) == 2
 
-            # Store original session ID
+            # Mutate session state to simulate an active session
             assert app.session_state is not None
-            original_session_id = app.session_state.session_id
+            app.session_state.session_id = "active-session-123"
 
             # Clear chat via action (available through command palette)
             await app.action_clear_chat()
@@ -277,9 +277,11 @@ async def test_clear_chat_resets_session(temp_db_path: Path):
             # Verify messages cleared
             assert len(chat_history.messages) == 0
 
-            # Verify session state reset (new session ID)
+            # Verify session state reset
             assert app.session_state is not None
-            assert app.session_state.session_id != original_session_id
+            assert app.session_state.session_id == ""
+            assert app.session_state.qa_history == []
+            assert app.session_state.citations == []
 
 
 @pytest.mark.asyncio