SDK-9: mesh-sdk takes no new seat-specific name (ADR 0613 §5, design 26 *Contracts modules*)

Every seat constant of mesh-sdk is mesh-contracts' generated name; the four whole seats' (BrokerSeat, CheckerSeat,
asks.Seat, buscompose.VaultSeat) are marked deprecated for their importers. The package walk of mesh-sdk's own check
refuses a string literal naming a defined seat or its subjects, and an exported name given to one, beyond
testdata/seat-names.txt, which lists what stands before the move (module names that equal a seat's among them) and
only shrinks. No new test function.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

go/asks/asks.go

@@ -15,13 +15,18 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	contractseats "git.novox.be/novox/mesh-contracts/go/seats"
 )
 
 // The seats (novox/hq ADR 0259 §3).
 const (
 	// Seat is held by the router: an ask and its cancel are its accepts, a warrant its event, each named by
 	// the asker.
-	Seat = "operator-channel"
+	//
+	// Deprecated: the seat is defined whole in mesh-contracts (operatorchannel.Seat, its subjects and message
+	// types); kept for its importers until their next change takes it from there (testdata/seat-names.txt).
+	Seat = contractseats.OperatorChannel
 	// ChannelSeat is the kinded bench a channel holds to show and say: its accepts carry the kind.
 	ChannelSeat = "channel"
 	// IntakeSeat is the kinded bench a channel holds to say what was chosen: its events and proofs carry