Avoid cold-start HealthKit observer registration for denied background types

[Copilot]

v14 introduced a cold-start regression where the native HealthKit sheet could flash briefly even when JS never called requestAuthorization. The behavior was isolated to the new background-delivery startup path added in v14, not to the existing read/query APIs.

• Root cause

  • BackgroundDeliveryManager registered HKObserverQuery instances for all persisted background types during app launch.
  • That happened before confirming enableBackgroundDelivery succeeded for each type, so denied/unavailable types could still be observed on cold start.

• Change

  • Gate observer registration on successful enableBackgroundDelivery(...).
  • Only start the HKObserverQuery after HealthKit accepts background delivery for that type.
  • Skip late async observer startup if teardown already ran.

• Impact

  • Preserves the v14 background-delivery architecture for authorized types.
  • Avoids cold-start observer setup for types HealthKit refuses, which is the likely trigger for the permission-sheet flash.

• Implementation sketch

  healthStore.enableBackgroundDelivery(for: sampleType, frequency: frequency) { success, error in
    if success {
      self.startObserverQuery(typeIdentifier: typeIdentifier, sampleType: sampleType)
    }
  }

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