sessionId property
SessionID continues an EXISTING sandbox, which is what makes runs stateful: the same filesystem, so one run's output file is the next run's input. Empty leases a fresh sandbox and the id it got comes back on the result.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? sessionId;