docs(openspec): add SDD artifact trail for recent alarm and EQ changes

Persist the exploration, proposal, spec, design, tasks, and
verify/archive reports produced during the multi-device EQ,
alarm-countdown, and notification-visual-polish SDD cycles.

openspec/changes/alarm-live-countdown/explore.md

@@ -0,0 +1,33 @@
+# Exploration: Alarm Live Countdown & Snooze Dismiss
+
+## Feature 1: Live countdown in pre-notice notification
+
+### Current state
+`PluriWaveAlarmReceiver.showPreNoticeNotification()` posts a single notification with hardcoded Spanish text `"Empieza en 30 minutos"`. No l10n, no update mechanism. Notification ID is deterministic (`53 * alarmId.hashCode() + 7`), enabling in-place updates.
+
+### Recommended approach (B)
+Compute remaining minutes at fire time: `(triggerAtMillis - System.currentTimeMillis()) / 60_000`. Use existing translated `durationMinutesOnly` key (`"{minutes} min"`) already available in all 13 locales.
+
+### Why not live updates
+- AlarmManager chain (30 PendingIntents): quota risk on API 31+
+- Foreground service: MIUI/OneUI/ColorOS kill aggressively (~60% of market)
+- Flutter Timer.periodic: only works when app is foregrounded
+
+## Feature 2: Snooze dismisses modal reliably
+
+### Current state
+`_posponer()` calls `navigator.pop()` but when app is launched from dead state via full-screen intent, Navigator stack is empty and `pop()` is a no-op. Screen stays visible.
+
+### Fix
+```dart
+if (navigator.canPop()) {
+  navigator.pop();
+} else {
+  SystemNavigator.pop();
+}
+```
+
+## Affected Files
+- `android/.../PluriWaveAlarmReceiver.kt` — compute remaining, l10n-ready text
+- `lib/pantallas/pantalla_alarma_sonando.dart` — canPop guard
+- `lib/l10n/app_*.arb` — new pre-notice l10n key if needed