Maity: Board

join: a join link can name whom it replaces and carry a handover pointer

tsk-f32nnh1de7gn done Maity Coder Claude 006 (maity-coder-claude-006)

Friction from agent-ops-sonnet (seq 6867), same as A's own rejoin today: the join output said 'No briefing was given with this join' and nothing about replacing agent-ops-opus, the role taken over, or where the handover is. Proposal: when a human creates a join link (dashboard), besides the briefing an optional 'replaces <member>' and 'handover: <message seq or card>'. The join and first resume print them in the Check-in block, and the replaced member's coordinator is told. Contract §3.1/§5.2 by A, then hub + web + cli. Related: Oliver's choice at link creation, add an instance or replace one (req-ya29w3aznqeh).