Absolute deadline as Unix milliseconds, or null.
Encoded bytes buffered for any one attached stream.
Encoded bytes buffered across every attached stream.
Messages buffered for any one attached stream.
Messages buffered across every attached stream.
Concurrent child action handlers.
Concurrent top-level action handlers.
Maximum encoded size of one incoming message.
Grace period with no streams, or null when disabled.
Validated, default-filled form of SessionOptions.