Receipts carried the clipboard text and weren't coverage-gated, so an ack could
echo content over the relay even when the clipboard stayed P2P. Now the receipt
carries fingerprint(text) (sha256[..8]) instead of the text, and the auto-ack
skips the SSE relay when a direct path covers the room — same rule as send().
Closes the last way content could reach the server once P2P is up.
Verified: prefer_direct still keeps the payload off the bus (only presence
relayed, no receipts), and receipt_demo still confirms delivery (matched by
device name now that the text is hashed).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Patrick Ecord
ee938600c3
