Whether notifications/progress may carry the optional message field.
The 2024-11-05 ProgressNotification params are {progressToken, progress,
total?} with NO message; message was introduced in 2025-03-26 and is
retained in every later version. Emitting it to a 2024-11-05 peer would
inject an out-of-schema key, so the server gates it on this predicate.
Whether notifications/progress may carry the optional message field. The 2024-11-05 ProgressNotification params are {progressToken, progress, total?} with NO message; message was introduced in 2025-03-26 and is retained in every later version. Emitting it to a 2024-11-05 peer would inject an out-of-schema key, so the server gates it on this predicate.