diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9ca997b0..a15204d9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,10 @@
 # Changelog
 ## [Unreleased]
 
+### Fixed
+
+- **TUI session context not updating**: The Chat TUI now generates a UUID `session_id` on mount and on chat clear, fixing background summarization which requires a non-empty `session_id`.
+
 ## [0.29.1] - 2026-02-10
 
 ### Fixed
diff --git a/haiku_rag_slim/haiku/rag/chat/app.py b/haiku_rag_slim/haiku/rag/chat/app.py
index 3c68a8ed..a53c8a47 100644
--- a/haiku_rag_slim/haiku/rag/chat/app.py
+++ b/haiku_rag_slim/haiku/rag/chat/app.py
@@ -156,6 +156,7 @@ class ChatApp(App):
         # Create agent and session state
         self.agent = create_chat_agent(self.config)
         self.session_state = ChatSessionState(
+            session_id=str(uuid.uuid4()),
             initial_context=self._initial_context,
             document_filter=self._document_filter,
         )
@@ -328,6 +329,7 @@ class ChatApp(App):
         # Reset context lock and session state (reset to CLI value)
         self._context_locked = False
         self.session_state = ChatSessionState(
+            session_id=str(uuid.uuid4()),
             initial_context=self._initial_context,
             document_filter=self._document_filter,
         )
diff --git a/tests/chat/test_chat_app.py b/tests/chat/test_chat_app.py
index f7b24142..3d09adf9 100644
--- a/tests/chat/test_chat_app.py
+++ b/tests/chat/test_chat_app.py
@@ -245,9 +245,25 @@ async def test_chat_history_thinking_indicator(temp_db_path: Path):
             assert len(list(thinking)) == 0
 
 
+@pytest.mark.asyncio
+async def test_chat_app_generates_session_id(temp_db_path: Path):
+    """Test that ChatApp generates a UUID session_id on mount."""
+    from haiku.rag.chat.app import ChatApp
+
+    mock_client = AsyncMock()
+    mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+    mock_client.__aexit__ = AsyncMock(return_value=None)
+
+    with patch("haiku.rag.chat.app.HaikuRAG", return_value=mock_client):
+        app = ChatApp(temp_db_path, read_only=True)
+
+        async with app.run_test():
+            assert app.session_state.session_id != ""
+
+
 @pytest.mark.asyncio
 async def test_clear_chat_resets_session(temp_db_path: Path):
-    """Test that clearing chat resets the session state."""
+    """Test that clearing chat resets the session state with a new session_id."""
     from haiku.rag.chat.app import ChatApp
     from haiku.rag.chat.widgets.chat_history import ChatHistory
 
@@ -266,9 +282,9 @@ 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
 
-            # Mutate session state to simulate an active session
-            assert app.session_state is not None
-            app.session_state.session_id = "active-session-123"
+            # Record the original session_id
+            original_session_id = app.session_state.session_id
+            assert original_session_id != ""
 
             # Clear chat via action (available through command palette)
             await app.action_clear_chat()
@@ -277,9 +293,10 @@ async def test_clear_chat_resets_session(temp_db_path: Path):
             # Verify messages cleared
             assert len(chat_history.messages) == 0
 
-            # Verify session state reset
+            # Verify session state reset with a new session_id
             assert app.session_state is not None
-            assert app.session_state.session_id == ""
+            assert app.session_state.session_id != ""
+            assert app.session_state.session_id != original_session_id
             assert app.session_state.qa_history == []
             assert app.session_state.citations == []