diff --git a/src/genesis/server/store.py b/src/genesis/server/store.py
index 18a3ab9..0ef47a9 100644
--- a/src/genesis/server/store.py
+++ b/src/genesis/server/store.py
@@ -197,6 +197,7 @@ class SessionStore:
 
     def delete_session(self, session_id: str) -> bool:
         with self._conn() as c:
+            c.execute("DELETE FROM chat_messages WHERE session_id = ?", (session_id,))
             cur = c.execute("DELETE FROM sessions WHERE session_id = ?", (session_id,))
         return cur.rowcount > 0
 
diff --git a/tests/test_server_store.py b/tests/test_server_store.py
index e5452c3..bd58b56 100644
--- a/tests/test_server_store.py
+++ b/tests/test_server_store.py
@@ -234,3 +234,12 @@ def test_list_sessions_no_project_returns_all(store):
     store.create_session("u1", name="A", project="stock")
     store.create_session("u1", name="B", project="other")
     assert len(store.list_sessions("u1")) == 2
+
+def test_delete_session_cascades_messages(store):
+    rec = store.create_session("u1", name="A", project="stock")
+    store.add_message(rec.session_id, "user", "hi")
+    store.add_message(rec.session_id, "assistant", "ok")
+    assert len(store.list_messages(rec.session_id)) == 2
+    ok = store.delete_session(rec.session_id)
+    assert ok is True
+    assert store.list_messages(rec.session_id) == []