desktop demo: successful native smoke logs IPC EPIPE during teardown

[luokerenx4]

On clean dev 0a10220d, macOS arm64, pnpm electron:smoke:demo completes all native demo checks and exits 0, but teardown logs Error: write EPIPE from sendAliceMessage -> fetchAliceWebRequest -> demo-main app protocol handler.

Passed checks include app protocol/preload, isolated Inbox/report/files/conversation, native companion visibility, sound settings, notification defaults/persistence, real Journal-to-background-pet privacy and safe Open. The error follows the final notification PASS and app quit.

Suspected lifecycle: demo-main.ts kills its fixture backend on before-quit while protocol requests may still be dispatched. Callback-based sendAliceMessage already prevents an unhandled ChildProcess error; the protocol request rejects and Electron reports the EPIPE. Establish teardown cancellation/closed-source handling before claiming stderr-clean native smoke. Keep actual unexpected IPC failures visible.

This is separate from #1685's user-visible destroyed-BrowserWindow exception. Deferred to avoid expanding that bounded notification-controller repair into shared IPC/protocol shutdown. No broker or production state was involved; the demo uses its existing disposable profile/backend.

[luokerenx4]

A candidate fix is open in Draft #1726, not merged. It retires the demo fixture source and cancels its in-flight requests before backend teardown while preserving unexpected errors from active sources.

Marking this as awaiting review and acceptance. The current-head clean build is green, but the remaining gate is a complete native macOS ARM64 demo smoke: original functional assertions pass, exit code is 0, and expected teardown produces no IPC EPIPE. Also check source isolation and that unexpected backend/send failures remain visible. The reported unit checks do not replace that native run.