The update poller and the chunk-error reload guard key on the target
version instead of disarming for the whole session, so a second deploy
re-arms the self-heal and a stale shell can no longer strand with
404ing chunks. Lazy chart imports retry once and mount inside a
per-card error boundary with a reload affordance — a failed chunk
degrades to one card instead of replacing the page. The JSON API
client attaches a fifteen-second timeout unless the caller brings its
own signal (the raw streaming path is exempt), chart queries surface
errors with a retry instead of rendering as an empty period, per-type
fetch failures reject instead of caching an empty series as fresh, and
the session and snapshot queries retry once on transient network or
server errors.
