wip feat: Request checkpoint

[stevensJourney]

Overview

This is the Swift SDK implementation of the Request Checkpoint proposal: https://github.com/orgs/powersync-ja/discussions/324

Related to:

• wip feat: Request Checkpoints powersync-service#696
• wip: write checkpoints and checkpoint requests powersync-sqlite-core#198

This adds a new requestCheckpoint method which returns a CheckpointRequest. The CheckpointRequest instance exposes a waitForSync method which resolves once the request has been synced and applied to the client

    func refreshFromRemote(timeout: TimeInterval = 30) async throws {
        let checkpoint = try await powerSync.requestCheckpoint()
        try await checkpoint.waitForSync(timeout: timeout)
    }

The SDK is updated to cater for the Rust core and PowerSync service changes. The SyncStatus has been updated to expose the lastAppliedCheckpointRequestId - used to resolve checkpoint requests.

Demo

The PowerSyncExample has been updated to include a Pull to refresh action which will show a loading spinner until a checkpoint request has been resolved.

In order to showcase the functionality a bit better, a new Admin page has been added to the demo which conveys the SyncStatus. In the demo below, we go offline, create 50k todos which will be synced then connect and await a checkpoint request. We can see the download progress reach 100%, but the data is only available after the checkpoint has been applied locally - the checkpoint request correctly keeps the operation in a loading state until the data is actually available.

request-checkpoint.mp4

Todos

• This implementation currently hardcodes a Checkpoint mode to the checkpoint-request feature. We should add compatibility checks for this
• This PR contains potential workarounds for some observed weirdness in SyncStatus results - these might need to be separate fixes/PRs (needs further investigation)

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AI disclosure: This work was assisted by Codex GPT 5.5. I manually guided and reviewed all the changes.