Function moq_client_defaults 

#[unsafe(no_mangle)]
pub extern "C" fn moq_client_defaults() -> moq_client_config

The settings moq_session_connect dials with when given NULL.

Behaviorally the same as a zeroed struct, so this is for display rather than for dialing: a settings UI can show the real numbers instead of hardcoding ones that go stale when a default is retuned. The knobs whose default depends on the backend (GSO, path MTU discovery, congestion control, the TLS root store) come back with their has_* flag false, since there is no single value to report.

Returned by value because there is nothing to fail: no handle to look up and no pointer to reject. Prefer a zeroed struct when you only mean to set a knob or two, and this when you want to read the numbers.