DSH Notification Chime Plugin: Show a System Notification While Waiting for a Reply or When a Conversation Turn Completes

The DSH ecosystem plugin `dsh-notify-ding` addresses the issue of developers overlooking background status in long-running or multi-session scenarios. This purely browser-based plugin proactively alerts users with browser system notifications and sounds when a session is waiting for a reply or changes status. It does not check page focus; it rings for any event in any session, and each request triggers only one ring. It takes effect after installation and a restart, and notification permission is required. Clicking a notification switches to the corresponding session, and multiple open tabs share the same ringing interval.