offlineProvider: a Notifier<bool> driven by a periodic /healthz
probe. Offline after N=3 consecutive failed probes; recovers on
the first success. Slow heartbeat when online (30s), faster when
offline (10s) so recovery is noticed quickly. 5s initial delay for
provider warmup; optimistic (false) until proven otherwise.
Deliberately NOT coupled to connectivityProvider — subscribing to
that StreamProvider eagerly mounts its 2s timeout and leaks a
pending Timer through widget tests (the MutationReplayer bug).
/healthz failing already covers interface-down. No .timeout()
wrapper either (dio's own timeouts bound the probe) so the only
Timers are the tracked initial+periodic, both cancelled via
ref.onDispose — the proven smoke-safe shape.
Wired in app.dart postFrame to start the poller. No UI yet; S4
gates system-playlist play + Shuffle-all on it.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
