feat(multiplayer): harden ranked arena admission

server/domain/ranked.go

@@ -11,12 +11,28 @@ type RankedParticipant struct {
 }
 
 type RankedArena struct {
-	RandomEnabled bool
-	ElevatedGoals bool
+	ID string
+}
+
+// rankedArenas is the server-owned eligibility registry for launch ranked
+// matches. It mirrors the floor-goal ArenaRegistry entries in the Godot
+// project, but deliberately excludes every elevated-goal variant until a
+// policy trained for that geometry is promoted.
+var rankedArenas = map[string]RankedArena{
+	"arena_01": {ID: "arena_01"},
+	"arena_02": {ID: "arena_02"},
+	"arena_03": {ID: "arena_03"},
+}
+
+// DefaultRankedArena supplies a safe server-owned eligibility decision while
+// the allocator-to-Godot match configuration channel is being completed. A
+// ranked proposal is never admitted based on a mutable command-line boolean.
+func DefaultRankedArena() RankedArena {
+	return rankedArenas["arena_01"]
 }
 
 func ValidateRankedAdmission(participants []RankedParticipant, arena RankedArena) error {
-	if len(participants) != 6 || !arena.RandomEnabled || arena.ElevatedGoals {
+	if len(participants) != 6 || !validRankedArena(arena) {
 		return fmt.Errorf("ranked admission requirements not met")
 	}
 	seenPlayers := make(map[string]bool, len(participants))
@@ -30,3 +46,8 @@ func ValidateRankedAdmission(participants []RankedParticipant, arena RankedArena
 	}
 	return nil
 }
+
+func validRankedArena(arena RankedArena) bool {
+	registered, ok := rankedArenas[arena.ID]
+	return ok && registered == arena
+}