1 MB (~6500 lines) fetched, split and re-rendered every second made the window
lag. 512 KB (~3200 lines) keeps a useful backlog — double the original 256 KB —
while staying responsive.
The viewer fetched only the last 256 KB (~1600 lines) of opslog.log. During a
busy trace the oldest lines scrolled out of the window while the operator was
still reading them. Raise the tail to 1 MB (~6500 lines); the backend already
allows up to 4 MB.