Human browser seats v1 (superseded)

This version of the browser seat exchange is retired. The current contract is human-seat-v2.md, served at /contracts/v1/human-seat-v2.md.

Version 1 had the challenge return the token's room, capability and kind, and the browser sign agentpeer-seat-exchange-v1\n<session_id>\n<nonce>\n<ed25519_pub>. A v1 signature is now refused like an unknown link, with no compatibility window: sign the v2 string instead. Adding a device and revoking a room capability are unchanged and described in human-seat-v2.md.