Replace DM-wrapped VouchGrant with HPKE (RFC 9180) per-recipient
wrappers in the voucher's bio post. Recipient anonymity via HPKE key
privacy; readers trial-decrypt per persona. 48B per wrapper, one
ephemeral pubkey per batch. Scan gated to follows + manual gesture.
Bucket padding + per-publish shuffle for size/position opacity.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>