The Tasks page polls the primary engine via the short-timeout client. While the
primary is GIL-busy generating it can't answer, so poll() hit its except branch and
returned the primary's tasks as EMPTY — the running generation vanished from the
page under load. Cache the primary's last-good task list (120s TTL) and reuse it
(marked stale) when the live poll fails, so an in-flight generation stays visible.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>