On every inbound clipboard the engine auto-sends a receipt back to the sender
(type:"receipt", to:sender, role:my-name, text:the-clipboard). Senders collect
them via Engine.receipts() -> [Receipt{from,name,source,text,ts}] so the UI can
show "delivered to iPhone" per sent item — visible read state, not manual asking.
Plumbing this required: SSE post now sends the full envelope (type/to/role), not
just text; the SSE stream forwards receipts as well as clipboards; RTC's raw-text
data channel skips non-clipboard messages (receipts ride SSE/LAN). Receipts
de-dupe across transports.
Proven by examples/receipt_demo.rs: A sends, B auto-acks, A.receipts() shows
"seen by Patrick's iPhone".
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Patrick Ecord
1fbe989675
