Major rework: from "outbox with unbounded retries" to a full offline-first engine. Persisted records from 0.1.x deserialize unchanged.

Added #

• Pull replication: SyncCollection<T> (fetchPage/applyPage), engine-owned watermarks (WatermarkStore, StorageWatermarkStore), pagination loop, page bounds, per-collection progress events. sync() now pushes then pulls.
• SyncOutbox write API: crash-safe submit(TaskDraft) (actions first, task as commit marker), appendAction, resetFailedActions, collectGarbage (orphan sweep), task/action lookups.
• TaskDraft / ActionHandle builder: auto IDs, auto idempotency keys, sequential chaining by default, explicit dependency graphs.
• $ref:<actionId>:<path> placeholders resolved by the engine into payloads; ref targets are implicit dependencies (cross-task supported).
• Typed errors: RetryableSyncException, PermanentSyncException, ConflictSyncException; lastError persisted on actions and tasks.
• RetryPolicy: bounded attempts + exponential backoff; escalation to failedPermanent (v1 retried forever with no delay).
• Typed event stream SyncEngine.events (SyncEvent hierarchy) and a SyncReport return value; legacy statusStream now carries real counters.
• Multi-dependency actions (QueueAction.dependencies); dependsOn kept as a deprecated single-value view.
• Injectable Clock; explicit start()/stop() lifecycle (constructor no longer subscribes to connectivity).
• Missed-sync coalescing: sync() during a run merges into a follow-up run.
• Empty-task guard: a task with no actions past a grace period fails loudly instead of being vacuously marked synced.
• In-memory implementations for every port + a full test suite.

Changed #

• QueueService interface gained getAllTasks() and clearTasks().
• sync() returns SyncReport (was void).
• An offline sync() reports skippedOffline instead of silently returning.

Migration notes (0.1.x → 0.2.0) #

• Call await engine.start() after registering processors/collections — connectivity reaction is no longer automatic on construction.
• Implement the two new QueueService methods.
• Replace hand-built QueueTask/QueueAction enqueueing with outbox.submit(TaskDraft...).
• Replace "fetch remote data" pseudo-actions with registered SyncCollections; keep a no-op processor for the old action type so queues persisted by previous app versions complete cleanly.

Initial extraction: queue models, storage/connectivity interfaces, multi-pass sync engine with single-parent dependencies, foreground BackgroundSyncManager.