Append a per-stream session token to the legacy message-POST URI so the leading
endpoint event tells a client where to POST AND which stream its replies
belong to. The token is added as a sessionId query parameter, preserving any
existing query string already present on the path.
Append a per-stream session token to the legacy message-POST URI so the leading endpoint event tells a client where to POST AND which stream its replies belong to. The token is added as a sessionId query parameter, preserving any existing query string already present on the path.