Initialize standard session state namespaces on session creation

Ensures context, temp, user, and system scopes always exist as
empty dicts so CEL expressions like has(context.experiments) evaluate
to false instead of throwing when no initial_state is provided.

Author: hardbyte

app/repositories/chat_repository.py

@@ -61,7 +61,16 @@ async def create_session(
         trace_level: Optional[str] = None,
     ) -> ConversationSession:
         """Create a new conversation session with initial state."""
-        state = initial_state or {}
+        # Ensure standard scope namespaces always exist so CEL
+        # expressions like has(context.foo) don't throw when
+        # the top-level scope key is missing entirely.
+        state = {"context": {}, "temp": {}, "user": {}, "system": {}}
+        if initial_state:
+            for key, value in initial_state.items():
+                if key in state and isinstance(value, dict):
+                    state[key].update(value)
+                else:
+                    state[key] = value
         state_hash = self._calculate_state_hash(state)
 
         session = ConversationSession(