[Divergence] Rust SDK replaces the BackendConnector trait with Authenticator and MutationUploader (powersync-native #46) #726

What's changing: The Rust SDK removes the BackendConnector trait as a breaking change and splits it into Authenticator (resolve_credentials returns a JWT, which the implementation can cache, plus invalidate_credentials and the optional post_checkpoint_request) and MutationUploader (upload, which an async closure can implement). The PowerSync endpoint is now set statically on SyncOptions instead of being returned in PowerSyncCredentials. SyncOptions::new takes both an authenticator and an uploader, and the new SyncOptions::download_only and SyncOptions::upload_only take only one and run unidirectional sync. The change is unreleased (changelog entry "0.2.0 (unreleased)").

High priority — existing docs are now inaccurate or incomplete

• Rust SDK Reference (https://docs.powersync.com/client-sdks/reference/rust), "Integrate with Your Backend" step: the connector description and example use impl BackendConnector with fetch_credentials returning PowerSyncCredentials with an endpoint, and upload_data. The example and the SyncOptions::new(MyBackendConnector { ... }) calls in the connect snippet and the checkpoint mode snippet no longer compile.
• Get Started (https://docs.powersync.com/intro/setup-guide), Rust tabs: the connector example uses use powersync::{BackendConnector, PowerSyncCredentials, ...}, impl BackendConnector, and SyncOptions::new(MyBackendConnector { ... }), which no longer match the SDK.
• Usage Examples (https://docs.powersync.com/client-sdks/usage-examples), Rust upload section: tells readers to implement upload_data on their BackendConnector, which no longer exists.
• Checkpoint Requests (https://docs.powersync.com/client-sdks/advanced/checkpoint-requests), Rust tab and the platform list: says to implement BackendConnector::post_checkpoint_request. The method is now on Authenticator.

For reviewer consideration — worth documenting

• The download-only and upload-only modes (SyncOptions::download_only and SyncOptions::upload_only) are new opt-in capabilities. Rust SDK Reference is the page that covers connecting and configuring SyncOptions. The Kotlin equivalent is tracked in [Divergence] Kotlin SDK splits PowerSyncBackendConnector into Authenticator and MutationUploader, with download-only and upload-only connect() overloads (powersync-kotlin #380) #717.

Source PR: powersync-ja/powersync-native#46 — merged 2026-10-27

Filed automatically by Claude Code (claude-sonnet-5-5). A human must verify the scope, prepare the docs PR, and publish it only once this update has been released.