Implement Background Sync and Periodic Sync (Minimal)

[FlorianRappl]

Proposal

Add a minimal registration surface for one-off and periodic sync tasks tied to Service Worker registrations.

Scope:

• Expose sync and periodicSync managers on service worker registration.
• Support register, getTags, and unregister patterns.
• Add scheduler hook via platform interface.
  Technical Notes:
• Keep scheduling backend injectable and deterministic in tests.
• Validate origin and registration constraints.
  Acceptance Criteria:
• Tags can be registered, queried, and removed.
• Duplicate registration semantics are consistent.
• Tests verify schedule dispatch invocation and permission gating.
  Out of Scope:
• Real OS wake-up scheduling behavior.
• Complex power/network heuristics.

Description

Introduce minimal Background Sync and Periodic Background Sync support on service worker registrations, including register/getTags/unregister operations backed by an injectable scheduler.

Background

Apps often defer network operations to stable connectivity windows. Even a reduced API helps test deferred work orchestration and tag-based job management.

Specification

• Background Sync: https://wicg.github.io/background-sync/spec/
• Periodic Background Sync: https://wicg.github.io/background-sync/spec/PeriodicBackgroundSync-index.html