1 files changed, 58 insertions, 0 deletions
diff --git a/internal/player/roomset_test.go b/internal/player/roomset_test.go
index 2b6b9cb..38bd993 100644
--- a/internal/player/roomset_test.go
+++ b/internal/player/roomset_test.go
@@ -1,6 +1,8 @@
 package player
 
 import (
+	"encoding/base64"
+	"encoding/binary"
 	"strings"
 	"testing"
 
@@ -85,3 +87,59 @@ func TestRoomSetMarshalEmpty(t *testing.T) {
 		t.Errorf("MarshalYAML empty = %q, want empty string", s)
 	}
 }
+
+// Sparse, high room IDs are the reason RoomSet is not a dense bitset: the
+// encoding must stay proportional to the visited count, not the largest ID.
+func TestRoomSetSparseEncodingIsCompact(t *testing.T) {
+	var rs RoomSet
+	for _, id := range []int{1001, 1002, 1003, 2001, 2006, 99999301} {
+		rs.Add(id)
+	}
+	data, err := yaml.Marshal(PlayerStats{RoomsVisited: rs})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	if len(data) > 200 {
+		t.Fatalf("encoding is not compact for sparse IDs: %d bytes\n%s", len(data), data)
+	}
+
+	var loaded PlayerStats
+	if err := yaml.Unmarshal(data, &loaded); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	for _, id := range []int{1001, 1002, 1003, 2001, 2006, 99999301} {
+		if !loaded.RoomsVisited.Has(id) {
+			t.Errorf("round trip lost room %d", id)
+		}
+	}
+	if loaded.RoomsVisited.Has(5000) {
+		t.Error("round trip invented room 5000")
+	}
+}
+
+// The prototype has no legacy formats: anything without the v1 prefix is a
+// hard error rather than a silently-decoded old bitset.
+func TestRoomSetRejectsUnknownEncoding(t *testing.T) {
+	var wrap struct {
+		Visited RoomSet `yaml:"rooms_visited"`
+	}
+	if err := yaml.Unmarshal([]byte("rooms_visited: AQIDBA==\n"), &wrap); err == nil {
+		t.Fatal("expected error for unprefixed encoding")
+	}
+	if err := yaml.Unmarshal([]byte("rooms_visited: [7, 42, 900]\n"), &wrap); err == nil {
+		t.Fatal("expected error for YAML sequence encoding")
+	}
+}
+
+func TestRoomSetRejectsOutOfRangeDelta(t *testing.T) {
+	// A valid uvarint delta above roomSetMaxID must fail rather than wrap or
+	// synthesize an absurd room ID.
+	buf := binary.AppendUvarint(nil, uint64(roomSetMaxID)+1)
+	encoded := roomSetV1Prefix + base64.StdEncoding.EncodeToString(buf)
+	var wrap struct {
+		Visited RoomSet `yaml:"rooms_visited"`
+	}
+	if err := yaml.Unmarshal([]byte("rooms_visited: "+encoded+"\n"), &wrap); err == nil {
+		t.Fatal("expected error for out-of-range delta")
+	}
+}