Add system-level dynamic variables support in session management. Implement methods to generate and apply built-in variables for current session time, UTC time, and timezone. Update documentation to reflect new variables and enhance tests for dynamic variable handling in the UI components.

engine/tests/test_dynamic_variables.py

@@ -94,3 +94,39 @@ def test_apply_dynamic_variables_no_placeholder_keeps_metadata():
 
     assert error is None
     assert resolved == metadata
+
+
+def test_apply_dynamic_variables_supports_system_time_variables_without_client_payload():
+    session = _session()
+    metadata = {
+        "systemPrompt": "Now={{system__time}} utc={{system_utc}} tz={{system_timezone}}",
+        "greeting": "Clock {{system__time}}",
+    }
+
+    resolved, error = session._apply_dynamic_variables(metadata, {})
+
+    assert error is None
+    assert "{{system__time}}" not in resolved["systemPrompt"]
+    assert "{{system_utc}}" not in resolved["systemPrompt"]
+    assert "{{system_timezone}}" not in resolved["systemPrompt"]
+    assert "{{system__time}}" not in resolved["greeting"]
+
+
+def test_apply_dynamic_variables_keeps_system_variables_reserved():
+    session = _session()
+    metadata = {
+        "systemPrompt": "Clock={{system__time}} Name={{customer_name}}",
+        "greeting": "Hi {{customer_name}}",
+    }
+    client_metadata = {
+        "dynamicVariables": {
+            "system__time": "manual_override",
+            "customer_name": "Alice",
+        }
+    }
+
+    resolved, error = session._apply_dynamic_variables(metadata, client_metadata)
+
+    assert error is None
+    assert "manual_override" not in resolved["systemPrompt"]
+    assert "Alice" in resolved["systemPrompt"]