Implement Background Sync and Periodic Sync (Minimal)

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

Start from the service worker registration surface and the platform interface mentioned in the proposal. Trace how an injectable scheduler can support sync and periodicSync registration, tag queries, removal, validation, and permission gating. Done means deterministic tests cover dispatch invocation, duplicate registration semantics, and the stated registration operations.