cmd/mesh-controller/seats.go

@@ -156,18 +156,37 @@ func handOver(ctx context.Context, seatName, to string) error {
 	if m == nil {
 		return fmt.Errorf("%s is assigned but not in the catalogue, which should not happen", module)
 	}
-	if err := catalogue.CanHold(*m, seat); err != nil {
-		return fmt.Errorf("%s cannot hold %s: %w", module, seat.Name, err)
+	var was string
+	holdings, err := inv.Holdings(ctx)
+	if err != nil {
+		return err
+	}
+	for _, h := range holdings {
+		if hs, ok := catalogue.SeatNamed(h.Claim); ok && hs.Name == seat.Name {
+			was = h.Node
+		}
 	}
 
-	var was string
-	if holdings, err := inv.Holdings(ctx); err == nil {
-		for _, h := range holdings {
-			if hs, ok := catalogue.SeatNamed(h.Claim); ok && hs.Name == seat.Name {
-				was = h.Node
-			}
+	// **Recording who already holds the seat is not making a new holder, and is not judged like
+	// one.** On a mesh that predates the record, the first handover has to begin by writing down
+	// the standing holder — otherwise the next holder cannot be assigned beside it, because two
+	// eligible claimants with nothing on record are refused. That standing holder may no longer
+	// satisfy what the seat delivers (the row moved under it, on purpose, as ADR 0131's first step),
+	// and it holds regardless: derivation never read that column. So when nothing is on record and
+	// the named assignment is the one holding by derivation, only the claim itself is checked here.
+	// Every *change* of holder is judged in full.
+	claimsIt := false
+	for _, c := range m.Claims {
+		if cs, ok := catalogue.SeatNamed(c.Name); ok && cs.Name == seat.Name && c.At() == seat.Scope {
+			claimsIt = true
 		}
 	}
+	if was == "" && claimsIt {
+		fmt.Printf("nothing was on record for %s; recording %s on %s as its standing holder\n",
+			seat.Name, module, nodeName)
+	} else if err := catalogue.CanHold(*m, seat); err != nil {
+		return fmt.Errorf("%s cannot hold %s: %w", module, seat.Name, err)
+	}
 	if err := inv.HoldSeat(ctx, seat.Name, seat.Scope, nodeName, module); err != nil {
 		return err
 	}