[Fix] Keep uploading when a write races the write checkpoint

[bean1352]

What's wrong

When the CRUD queue drains, the upload loop requests a write checkpoint. If a local write lands inside that window, updateLocalTarget returns false because it found new CRUD, but false is also its "nothing left to upload" answer. The loop can't tell those apart, so it breaks out while the row is still in ps_crud.

The sync core then refuses every checkpoint with "Could not apply checkpoint due to local data". Usually the racing write's own notification is latched while the loop is busy and wakes it again right after it exits, so this shows up as a short stall.

The fix

Ask the adapter whether CRUD is still pending before breaking, and go round again if it is. This covers both cases where updateLocalTarget reports a race, including the sequence updated branch.

hasCrud() is only reached after nextCrudItem() returned null, so a true result means new data really did arrive during the round trip. If a connector doesn't complete its batch, the existing "previously encountered CRUD item" guard still catches that on the next pass, so this can't spin.

AI disclosure

I used Opus 5 to help research the original bug report, narrow down where the fault could be, and apply the fix. I reviewed and supervised the work.

[changeset-bot]

🦋 Changeset detected

Latest commit: 44914ed

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
@powersync/shared-internals	Patch
@powersync/adapter-sql-js	Patch
@powersync/capacitor	Patch
@powersync/node	Patch
@powersync/react-native	Patch
@powersync/web	Patch
@powersync/diagnostics-app	Patch

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[simolus3]

The loop can't tell those apart, so it breaks out while the row is still in ps_crud.

Shouldn't the new write also have triggered a crud trigger? If we change crudUploadLoop to acquire the wait notification promise before the rest of the upload, does that work?

  private async crudUploadLoop(signal: AbortSignal, options: ResolvedSyncOptions): Promise<void> {
    while (!signal.aborted) {
      const crudChangeNotification = this.crudUploadNotifier.waitForNotification(signal);
      await Promise.all([
        // Start the initial CRUD upload on connect. Then, keep polling until we're done.
        this._uploadAllCrud(signal, options),
        this.delayRetry(signal, options.crudUploadThrottleMs)
      ]);

      await crudChangeNotification;
    }
  }