Function err_is_terminal_persistence_retained 

pub fn err_is_terminal_persistence_retained(err: &Error) -> bool

True when err is the typed TerminalPersistenceRetained marker (a terminal write failed and the run stayed active with its claim intact), as opposed to any other fault. Lets a caller in another module or crate (e.g. the gateway cancel endpoint) render it as retryable backpressure rather than reporting the run as cancelled, without depending on the private struct.