[Divergence] Native SDK replaces async_tasks().spawn_with with automatic task spawning on connect/disconnect (powersync-native #40)

[benitav]

What's changing: The native/Rust SDK's connect() now spawns the sync tasks itself and disconnect() waits for them to finish, replacing the previous model where callers spawned tasks manually via PowerSyncDatabase::async_tasks() before connecting. This is a breaking change: async_tasks() is removed, the Timer trait is renamed AsyncRuntime and gains a required spawn method, and PowerSyncEnvironment::tokio_timer() / async_io_timer() are renamed to tokio() / async_io(executor) (the latter now takes an Arc<Executor> argument).

High priority — existing docs are now inaccurate or incomplete

• Rust SDK Reference (https://docs.powersync.com/client-sdks/reference/rust), "Database Setup" section: the Tokio and smol tabs call PowerSyncEnvironment::tokio_timer() / async_io_timer() and db.async_tasks().spawn_with_tokio() / spawn_with(smol::spawn) before connecting; the "Other" tab documents the same Timer trait and PowerSyncDatabase::async_tasks() model. None of these symbols exist anymore.
• Get Started (https://docs.powersync.com/intro/setup-guide), Rust example in the "Instantiate the PowerSync Database" step: the code and its surrounding comment show PowerSyncEnvironment::tokio_timer() and db.async_tasks().spawn_with_tokio() (with a note that other runtimes use spawn_with), the same removed API.

For reviewer consideration — worth documenting

• The replacement AsyncRuntime trait (delay_once plus a new spawn method) and the PowerSyncTask handle it returns (cancel(), cancel_and_join(), join()) are the new way to wire up an async runtime; the two affected pages above are where this should replace the removed content.

Source PR: powersync-ja/powersync-native#40 — merged 2026-09-21.

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