[High] iOS: firing notifications and Live Activity stop working once the app is backgrounded

[BenSeverson]

Summary
All status detection — the "Firing Complete" / "Kiln Error" notifications and Live Activity updates — is driven by the WebSocket in KilnStore.handleWebSocketUpdate. iOS suspends the app (and the socket) within seconds of backgrounding, and the app declares no background modes, no scenePhase handling, and starts the Live Activity with pushType: nil and staleDate: nil.

Firings run 8–12 hours with the phone in a pocket. In practice:

• The completion/error notifications are gated on the app being non-active (NotificationManager.swift:26) yet require the WS to be alive — a nearly empty intersection. The safety-relevant "Kiln Error / check kiln immediately" alert will essentially never fire.
• The lock-screen Live Activity freezes at its last value and presents stale temperature as current, indefinitely (staleDate: nil at FiringActivityManager.swift:29-31, 57).

Location

• ios/Bisque/Bisque/State/KilnStore.swift:104-123 (WS-driven transitions)
• ios/Bisque/Bisque/LiveActivity/FiringActivityManager.swift:29-31
• ios/Bisque/Bisque/Notifications/NotificationManager.swift:26
• No scenePhase handling anywhere in the app target.

Fix direction (increasing effort)

1. Set a staleDate (~60–90s) on Live Activity content so stale data renders as stale.
2. Refresh status and restart the WS on scenePhase == .active.
3. For real background delivery: the firmware already has a webhookUrl setting — documenting/wiring a push bridge like ntfy for completion/error events closes the safety gap without running push infrastructure. Live Activity push updates (ActivityKit push tokens) would need an APNs relay, a much bigger lift for a LAN-only device.

[BenSeverson]

Closing for the two parts that are fixed, in #253. The third — the one that closes the safety gap — is now tracked on its own as #254.

Fixed (#253):

• staleDate on Live Activity content, 90 s. Worth noting the first attempt at this was inert: setting staleDate only flips context.isStale, and ActivityKit does not change the rendering, so a frozen temperature went on looking exactly as current. Both the lock screen and all four Dynamic Island presentations now dim the reading, and the countdown is replaced rather than dimmed — "~2h remaining" extrapolated from a frozen frame is a claim, not a stale observation. The terminal "Complete" content keeps no staleDate, since a finished firing shouldn't age into looking like a lost connection.
• Resync on scenePhase == .active — refreshes /status and restarts the socket. Previously the socket came back dead while connectionState still read .connected.

Two bugs surfaced while doing that, both fixed in the same PR and neither visible from this issue:

• The naive reconnect caused continuous socket churn. disconnect() cancels the receive loop's task, but the catch block runs regardless (Task.isCancelled guards loop entry), and its main-actor hop lands after connect() has restored shouldReconnect — so it schedules a reconnect that cancels the healthy socket, whose loop schedules the next, at 1–8 s intervals indefinitely. Fixed with a generation stamp per connection.
• A status transition that happened while suspended was swallowed permanently. refreshAll assigned previousStatus directly, so the next frame carried the same value and the difference became undetectable — the Live Activity was never ended and peakTempC carried its high-water mark into the next firing's completion notification. The same lie [Low] iOS: completion notification reports transition-time temp as "peak" and hardcodes °C #146 was about, arriving by a different route.

Not fixed — see #254: the "Kiln Error / check kiln immediately" alert still requires the app to be running, so it essentially never fires. Closing that needs either the firmware's existing webhookUrl pointed at a push service, or a first-party APNs relay — infrastructure choices rather than a patch, which is why it's a separate issue with the options and trade-offs written out.

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