fix: Potential Multitab Transaction Issues With IndexedDB

[stevensJourney]

Problem

A db transaction death-loop could occur when using IndexedDB across multiple tabs, manifesting as the error:

cannot start a transaction within a transaction

This happens when a tab holding an active SQLite transaction is closed before committing or rolling back that transaction. Since IndexedDB shares a single SQLite connection (via a shared web worker) across all tabs, the uncommitted transaction persists and blocks subsequent transaction attempts.

Root Cause

• Each tab shares its SQLite connection with the shared sync worker
• The shared DBAdapter can be closed during an active transaction (e.g., when a tab closes)
• Uncommitted transactions remain active on the shared connection
• Subsequent BEGIN statements fail because a transaction is already in progress

Solution

This PR implements a connection "hold" mechanism:

1. Hold acquisition: A hold is created when a worker starts using a connection
2. Hold release: The hold is released when work completes normally
3. Orphaned hold detection: If the shared worker detects a hold changed without being properly released (indicating the tab closed mid-transaction), it executes ROLLBACK to clean up the orphaned transaction

This ensures transactions are always resolved, even when tabs close unexpectedly.

[changeset-bot]

🦋 Changeset detected

Latest commit: 8fc41a8

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[rkistner]

Happy with the overall approach - just have a minor comment on the holds that may affect performance.