fix(multiplayer): fence roster topology at persistence

server/store/assignment_sql_test.go

@@ -57,4 +57,14 @@ func TestSignedRosterRequiresCryptographicVerification(t *testing.T) {
 	}); err != nil {
 		t.Fatalf("valid signature rejected: %v", err)
 	}
+	wrongTeam := signed
+	wrongTeam.Authorisation.Slot = 3
+	wrongTeam.Authorisation.Team = 0
+	if err := validateSignedRosterEntry(assignment, wrongTeam, func([]byte, []byte) bool { return true }); err == nil {
+		t.Fatal("team/slot mismatch accepted")
+	}
+	duplicate := signed
+	if err := SaveVerifiedAssignmentRoster(nil, nil, assignment, []domain.SignedJoinAuthorisation{signed, duplicate}, func([]byte, []byte) bool { return true }); err == nil {
+		t.Fatal("duplicate roster player accepted")
+	}
 }