With background throttling on, Chromium wakes a hidden, silent page's
timers at most once per minute after five minutes, so a portal that asks
for get_events every 30 s would see pings at half its cadence while the
window is minimized. Tick the watchdog from a dedicated worker
(createBackgroundInterval, an inline blob worker allowed by the renderer
CSP), whose timers are not subject to page throttling. It falls back to a
page setInterval where no worker is available or the worker fails to load.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
