Option: play the notification sound only when nothing else is waiting

[ToukoUrsin]

I keep notification sound on so I know when an agent needs me. With many parallel threads, the sound plays for every thread that finishes, even when several finished threads are already waiting for me. At that point the chime carries no information and I start ignoring it. What I actually want: when everything is working, ping me for the first one that finishes; after that I'm already in the app and see the rest.

Proposal: a client setting, off by default, shown under Thread notifications when a sound mode is selected: "Sound only when nothing else is waiting". When on, the completion and input sounds are skipped if another non-archived, unsettled, unsnoozed thread (in any connected environment) was already waiting on me before this event: finished, asking, awaiting approval, or failed. Toasts and system notifications stay as they are. Settling or snoozing handled threads brings the sound back for the next one.

It's a small client-only change in the existing notification coordinator. I have an implementation ready (tests, lint and typecheck pass) if the direction makes sense.

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AI-written: drafted and implemented with Claude Code (Claude Opus 5.5) on my behalf; I reviewed and asked for it.