FeatureDiscoveryService<E extends Object> class

Orchestrates feature-discovery tips. Parameterized on E — the consumer- defined event type (typically an enum) whose values are emitted from screens as emit(context, MyEvent.onFoo, ctx).

Usage (typically a single instance per app, held in a top-level final or exposed through your DI / provider framework):

enum AppEvent { onStartupTick, onProductViewed }

final discovery = FeatureDiscoveryService<AppEvent>()
  ..registerAll([
    DiscoveryTip<AppEvent>(
      id: 'welcome_banner',
      priority: DiscoveryPriority.standard,
      triggers: {AppEvent.onStartupTick},
      shouldShow: (ctx) async => ctx.appLaunches >= 2,
      presentation: BannerPresentation(/* ... */),
    ),
  ]);

Priorities:

• critical — always evaluated, ignores session lock, can chain with other critical tips in a single emit (e.g. permissions, data disclosures).
• standard / optional — respect the session lock; claim the lock and end the chain when they fire.
• tip — respects the session lock AND is suppressed by a held lock.

Only one non-critical tip runs per session-lock window. The lock is cleared automatically when onAppResumed detects a background long enough (see backgroundResetThreshold), or manually via resetSession.