fix: enforce ranked match promotion size

server/store/match_sql.go

@@ -78,6 +78,9 @@ func CreateMatchFromAcceptedProposal(ctx context.Context, db *sql.DB, plan Accep
 		if proposalState != string(domain.Accepted) {
 			return fmt.Errorf("proposal is not accepted")
 		}
+		if !validAcceptedPlaylistCount(domain.Playlist(playlist), len(plan.Players)) {
+			return fmt.Errorf("accepted proposal playlist does not match player count")
+		}
 		participants, err := acceptedProposalParticipants(ctx, tx, plan)
 		if err != nil {
 			return err
@@ -110,6 +113,13 @@ func CreateMatchFromAcceptedProposal(ctx context.Context, db *sql.DB, plan Accep
 	})
 }
 
+func validAcceptedPlaylistCount(playlist domain.Playlist, count int) bool {
+	if playlist == domain.Ranked {
+		return count == 6
+	}
+	return playlist == domain.Casual && count >= 2 && count <= 6
+}
+
 func validAcceptedMatchPlan(plan AcceptedMatchPlan) bool {
 	if plan.MatchID == "" || plan.ProposalID == "" || (plan.Region != "EU" && plan.Region != "NA") || plan.Protocol < 1 || len(plan.Players) < 2 || len(plan.Players) > 6 {
 		return false

server/store/match_sql_test.go

@@ -50,6 +50,15 @@ func TestAcceptedMatchPlanRejectsInvalidPlansBeforeDatabaseUse(t *testing.T) {
 	}
 }
 
+func TestAcceptedMatchPromotionHonoursPlaylistSizeInvariant(t *testing.T) {
+	if validAcceptedPlaylistCount(domain.Ranked, 5) || !validAcceptedPlaylistCount(domain.Ranked, 6) {
+		t.Fatal("ranked accepted-match count invariant is wrong")
+	}
+	if validAcceptedPlaylistCount(domain.Casual, 1) || !validAcceptedPlaylistCount(domain.Casual, 2) || validAcceptedPlaylistCount("other", 6) {
+		t.Fatal("casual accepted-match count invariant is wrong")
+	}
+}
+
 func TestMatchPlayersFromTeamsUsesDeterministicTeamSlots(t *testing.T) {
 	teams := domain.Teams{
 		Team0: []domain.Candidate{{PlayerID: "bravo"}, {PlayerID: "alpha"}},