feat: gate proposals on formed match policy

server/domain/formation.go

@@ -0,0 +1,72 @@
+package domain
+
+import (
+	"fmt"
+	"time"
+)
+
+type PreparedProposal struct {
+	Proposal     Proposal
+	CasualLineup []CasualSlot
+}
+
+// PrepareProposal is the boundary between matchmaking and proposal state. It
+// never creates a proposal for a casual formation without one human per team,
+// or for a ranked formation whose verified identity/arena metadata fails the
+// ranked admission policy.
+func PrepareProposal(id string, playlist Playlist, formation MatchFormation, rankedParticipants []RankedParticipant, arena RankedArena, now time.Time) (PreparedProposal, error) {
+	if len(formation.Selection.Players) < 2 || len(formation.Selection.Players) > 6 {
+		return PreparedProposal{}, fmt.Errorf("invalid formed player count")
+	}
+	playerIDs := make([]string, 0, len(formation.Selection.Players))
+	seen := make(map[string]bool, len(formation.Selection.Players))
+	for _, player := range formation.Selection.Players {
+		if player.PlayerID == "" || seen[player.PlayerID] {
+			return PreparedProposal{}, fmt.Errorf("invalid formed player identity")
+		}
+		seen[player.PlayerID] = true
+		playerIDs = append(playerIDs, player.PlayerID)
+	}
+	var lineup []CasualSlot
+	switch playlist {
+	case Casual:
+		participants := make([]ConnectParticipant, 0, len(formation.Selection.Players))
+		for _, player := range formation.Teams.Team0 {
+			participants = append(participants, ConnectParticipant{PlayerID: player.PlayerID, Team: 0})
+		}
+		for _, player := range formation.Teams.Team1 {
+			participants = append(participants, ConnectParticipant{PlayerID: player.PlayerID, Team: 1})
+		}
+		var err error
+		lineup, err = BuildCasualLineup(participants)
+		if err != nil {
+			return PreparedProposal{}, err
+		}
+	case Ranked:
+		if len(rankedParticipants) != len(playerIDs) {
+			return PreparedProposal{}, fmt.Errorf("ranked metadata does not match formed players")
+		}
+		metadata := make(map[string]bool, len(rankedParticipants))
+		for _, participant := range rankedParticipants {
+			metadata[participant.PlayerID] = true
+		}
+		if len(metadata) != len(playerIDs) {
+			return PreparedProposal{}, fmt.Errorf("ranked metadata has duplicate or unknown players")
+		}
+		for _, playerID := range playerIDs {
+			if !metadata[playerID] {
+				return PreparedProposal{}, fmt.Errorf("ranked metadata missing formed player")
+			}
+		}
+		if err := ValidateRankedAdmission(rankedParticipants, arena); err != nil {
+			return PreparedProposal{}, err
+		}
+	default:
+		return PreparedProposal{}, fmt.Errorf("unsupported playlist")
+	}
+	proposal, err := NewProposal(id, playlist, playerIDs, now)
+	if err != nil {
+		return PreparedProposal{}, err
+	}
+	return PreparedProposal{Proposal: proposal, CasualLineup: lineup}, nil
+}