Use cloneable abort reason for shared sync port close

[longfellowone]

Summary

• Ensure abort reasons used when closing shared sync client ports are cloneable across Comlink.
• Add a regression test for both credentials and upload abort paths.

Changes

• SharedSyncImplementation now aborts with a plain string reason when removing a port.
• New tests in shared_sync_abort_reason.test.ts cover fetch-credentials and upload abort paths.
• Changeset for @powersync/web.

Tests

• pnpm --filter @powersync/common run build
• pnpm --filter @powersync/web run build:tsc
• pnpm vitest --run tests/shared_sync_abort_reason.test.ts

[changeset-bot]

🦋 Changeset detected

Latest commit: 4c2ea53

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

This PR includes changesets to release 2 packages

Name	Type
@powersync/web	Patch
@powersync/diagnostics-app	Patch

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[stevensJourney]

Could you please add more context for the issue this PR is trying to solve. Specifically the error you were observing before these changes.

From a quick refresher on the code. The abort reason is used to when aborting the uploadDataController, which will resolve the pending uploadCrud operation - Which means we don't actually pass any error from this flow. Which, from what I can tell, should not cause any clone errors when updating the SyncStatus for connected clients.

I haven't attempted to reproduce the issue this PR is trying to solve, but believe general cloning of unserializable Errors should be handled in #786 which will be merged and released soon.

powersync-js/packages/common/src/db/crud/SyncStatus.ts

Line 268 in e5253c9

protected serializeError(error?: Error) {

[longfellowone]

Saw DataCloneError while digging into #808. The only value that is directly set in that teardown path is the abort reason
passed from removePort(). Making that reason a plain string ensures signal.reason is cloneable (even if the abort Event itself still isn’t).

Based on my understanding, the path this targets (fetchCredentialsController):

• SharedSyncImplementation.fetchCredentials creates a Promise and sets abortController.signal.onabort = reject.
• removePort() aborts the controller, so the Promise rejects with the abort Event (whose target.reason is the
  string).
• If that rejection happens while the streaming loop is building a request (via AbstractRemote.getCredentials() →
  fetchCredentials()), the error can in some cases bubble to the streaming loop and be assigned to dataFlow.downloadError (see
  AbstractStreamingSyncImplementation.ts).
• SharedSyncImplementation.updateAllStatuses() broadcasts that status via Comlink, and SyncStatus.toJSON() does
  not sanitize errors.

[stevensJourney]

Saw DataCloneError while digging into #808. The only value that is directly set in that teardown path is the abort reason passed from removePort(). Making that reason a plain string ensures signal.reason is cloneable (even if the abort Event itself still isn’t).

Based on my understanding, the path this targets (fetchCredentialsController):

• SharedSyncImplementation.fetchCredentials creates a Promise and sets abortController.signal.onabort = reject.
• removePort() aborts the controller, so the Promise rejects with the abort Event (whose target.reason is the
  string).
• If that rejection happens while the streaming loop is building a request (via AbstractRemote.getCredentials() →
  fetchCredentials()), the error can in some cases bubble to the streaming loop and be assigned to dataFlow.downloadError (see
  AbstractStreamingSyncImplementation.ts).
• SharedSyncImplementation.updateAllStatuses() broadcasts that status via Comlink, and SyncStatus.toJSON() does
  not sanitize errors.

I see. The serialization in updateAllStatuses should be fixed in PR 786. It seems like the fetchCredentials error is actually caused by calling reject with the Abort event from onabort.

IMO, a nicer fix is to pair sending the AbortOperation as the Error for reject and serialising the error correctly.

          fetchCredentials: async () => {
            const lastPort = await this.getLastWrappedPort();
            if (!lastPort) {
              throw new Error('No client port found to fetch credentials');
            }
            return new Promise(async (resolve, reject) => {
              const abortController = new AbortController();
              this.fetchCredentialsController = {
                controller: abortController,
                activePort: lastPort
              };
-              abortController.signal.onabort = reject;
+              abortController.signal.onabort = () => {
+                reject(abortController.signal.reason);
+              };