When ?backend=<url> pointed at a server that wasn't running (e.g. user
forgot to start ruview-pointcloud serve before clicking Connect ESP32),
the viewer was retrying 10 Hz forever — flooding the console with
ERR_CONNECTION_REFUSED and offering no guidance about what was wrong.
Two fixes:
1. Replace setInterval(fetchCloud, 100) with self-rescheduling
setTimeout. On success: 250 ms steady cadence. On failure for an
explicit backend: 250 ms → 500 → 1 s → 2 s → 4 s → 8 s → 16 s →
capped at 30 s. Resets to 250 ms the moment the backend comes back.
Auto mode (Pages with no backend) still disables network entirely
after the first 404. Strict-live mode (?live=1) also backs off so
it doesn't spam.
2. Show an actionable status banner in the info panel when the chosen
backend is unreachable: the URL, the actual error string, the next
retry time, and the exact `cargo run` command to start the server.
Visitor sees the diagnosis instead of staring at a 'demo' badge
wondering why their ESP32 feed isn't visible.
The scene keeps animating (face mesh / synthetic) while the viewer
waits, so the tab never goes blank.
Co-Authored-By: claude-flow <ruv@ruv.net>
9a078e4ac8