- Add select_for_update() with transaction.atomic() to prevent race condition
when multiple users try to add the same showcase kit simultaneously
- Validate cart lock expiration when loading cart from Redis - showcase kits
with expired locks are now filtered out instead of being displayed
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Andrey Smakotin
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