data.msgs grew without bound (eventlog appended forever, also persisted in
the pickle), and ws.py replayed the entire history to every dashboard
client on connect - one JSON frame per message - making page reloads
progressively sluggish. Cap the buffer in eventlog() (configurable via
msg_buffer_size, default 500) and slice the WebSocket replay to the last
30, matching the window the HTTP render already uses.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>