fix(multiplayer): validate ranked arena paths durably

server/domain/ranked.go

@@ -49,6 +49,18 @@ func RankedArenaForProposal(proposalID string) RankedArena {
 	return rankedArenas[rankedArenaOrder[int(digest[0])%len(rankedArenaOrder)]]
 }
 
+// IsRankedArenaPath is the durable-store boundary for arena paths. Proposal
+// and allocation records must not accept a merely non-empty caller supplied
+// scene path, even when the caller bypasses matcher formation.
+func IsRankedArenaPath(path string) bool {
+	for _, arena := range rankedArenas {
+		if arena.Path == path {
+			return true
+		}
+	}
+	return false
+}
+
 func ValidateRankedAdmission(participants []RankedParticipant, arena RankedArena) error {
 	if len(participants) != 6 || !validRankedArena(arena) {
 		return fmt.Errorf("ranked admission requirements not met")

server/domain/ranked_test.go

@@ -48,6 +48,19 @@ func TestRankedArenaRegistryExcludesElevatedVariants(t *testing.T) {
 	}
 }
 
+func TestIsRankedArenaPathOnlyAllowsFloorGoalRegistry(t *testing.T) {
+	for _, path := range []string{"res://scenes/arena_01.tscn", "res://scenes/arena_02.tscn", "res://scenes/arena_03.tscn"} {
+		if !IsRankedArenaPath(path) {
+			t.Fatalf("eligible path %q rejected", path)
+		}
+	}
+	for _, path := range []string{"", "res://scenes/arena_01_elevated.tscn", "res://forged.tscn"} {
+		if IsRankedArenaPath(path) {
+			t.Fatalf("ineligible path %q accepted", path)
+		}
+	}
+}
+
 func TestRankedArenaForProposalIsStableAndRotatesEligibleRegistry(t *testing.T) {
 	first := RankedArenaForProposal("proposal-stable")
 	if first != RankedArenaForProposal("proposal-stable") {